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*****************************************
INSTRUCTION
MANUAL
FOR
DATAQUAD VERSION V3.29
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MODELS DXS and DXM
including
DATAPACKS 1, 2 and 3
Issue No.190
Manufactured by: Larimax Instruments
3 Devon Units, Hatchmoor Industrial Estate,
Torrington, Devon, EX38 7HP.
United Kingdom.
TABLE OF CONTENTS
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1. ORGANISATION OF THE MANUAL
2. UNPACKING AND INSTALLATION
2.1 UNPACKING AND CHECKING VISUAL DAMAGE
2.2 BEFORE YOU INSTALL THE ANALYSER
2.2.1 Vacuum chamber dimensions
2.2.2 Pressures in sputtering/etch/CVD systems
2.3 INSPECTING AND MOUNTING THE ANALYSER
2.3.1 Removing the mass filter cover
2.3.2 Mounting mass filter to vacuum chamber
2.4 CONNECTING ANALYSER, RF GENERATOR AND CONTROL UNIT
2.4.1 Installing the RF Generator
2.4.2 Electrical connections to control unit
3. INITIAL OPERATIONAL CHECK-OUT
3.1 VACUUM REQUIREMENTS
3.1.1 Maximum pressure
3.2 INITIAL OPERATIONAL CHECK-OUT
3.2.1 Locating the right key pads
3.2.2 Checking out Faraday detector DATAQUADS
3.2.3 Checking out dual detector DATAQUADS
4. CONTROL KEYS AND THEIR FUNCTIONS
4.0 INTRODUCTION AND PHOTOGRAPH
4.1 PANEL 1
4.1.1 POWER
4.2 PANEL 2
4.2.1 FIL #1 AND FIL #2
4.2.2 SEM (Electron Multiplier)
4.2.3 LEAK DETECT
4.3 PANEL 3
4.3.1 Arrow Keys
4.4 PANEL 4
4.4.1 INDEX
4.4.2 TABLE/GRAPH
4.4.3 PRINT
4.4.4 MAX PEAKS
4.4.5 RESET
4.4.6 BGND STORE
4.4.7 BGND DISPLAY
4.4.8 BGND SUB
4.5 PANEL 5
4.5.1 PEAK SELECT
4.5.2 CHANL
4.5.3 EN/DIS
4.5.4 ALARM
4.5.5 MASS
4.5.6 PREC
4.5.7 GAIN/AUTO
4.6 PANEL 6
4.6.1 BAR GRAPH
4.6.2 FULL SPAN
4.6.3 DISPLAY SPAN
4.6.4 MASS IDENT
4.6.5 MASS
4.6.6 PREC
4.6.7 GAIN/AUTO
4.7 PANEL 7
4.7.1 AUTO RUN
4.7.2 STOP/RUN
4.8 REAR PANEL
4.8.1 RF HEAD
4.8.2 ALARM OUT
4.8.3 PRINTER
4.8.4 AUX I/O
4.8.5 VOL
4.8.6 VIDEO
4.8.7 EXPANSION BUS
4.8.8 LINE CORD CONNECTION AND FUSES
4.8.9 RS232
5. MODES OF OPERATION
5.1 BAR GRAPH
5.1.1 What is a BARGRAPH?
5.1.2 When do You use BARGRAPH?
5.1.3 Getting Started
5.1 BAR GRAPH (Continued)
5.1.4 Changing the Mass Range
5.1.5 Changing the Mass at which the Scan Starts
5.1.6 Scanning the Full Span but Displaying Less
5.1.7 Scan Speed and Precision of Results
5.1.8 Identify Masses - Measure Partial Pressures
5.1.9 Gain and Sensitivity
5.1.10 Displaying Total Pressure
5.1.11 Background Store, Display and Subtract
5.1.12 Split Screen
5.1.13 Log/Log and Log/Lin Bar Graphs
5.1.14 Resetting Everything to Pre-set Values
5.1.15 Using the Electron Multiplier
5.1.16 Printing Out Results
5.2 PEAK SELECT
5.2.1 What is PEAK SELECT?
5.2.2 When to use PEAK SELECT?
5.2.3 Getting Started
5.2.4 Changing Mass to which Channel is Programmed
5.2.5 Temporarily Skipping some Channels
5.2.6 Level Alarms
5.2.7 Scan Time and the Precision of Results
5.2.8 Gain and Sensitivity
5.2.9 Displaying Total Pressure
5.2.10 Displaying in Either Table or Chart
5.2.11 Resetting Everything to Pre-Set Values
5.2.12 Using the Electron Multiplier
5.2.13 Printing
5.3 AUTOMATICALLY STORING EIGHT LARGEST PEAKS
5.3.1 MAX PEAKS and What It Means
5.3.2 Uses of MAX PEAKS
5.3.3 Entering MAX PEAKS
5.4 ANALOGUE DISPLAY
5.4.1 Interpreting ANALOGUE DISPLAY
5.4.2 Entering ANALOGUE DISPLAY
5.5 MULTICHANNEL TREND ANALYSIS
5.5.1 Uses of TREND ANALYSIS
5.5.2 Entering TREND ANALYSIS
5.6 LEAK DETECT
5.6.1 Detecting Leaks
5.6.2 Detecting Leaks with Other Gases
5.7 AUTO RUN
6. "INDEX" MENU
6.1 BAR GRAPH
6.1.1
to
6.1.6 Single Screen Bar Graph
6.1.7
to
6.1.13 Split Screen Bar Graph
6.1.14
to
6.1.17 LOG/LOG and LOG/LIN Displays
6.2 TREND ANALYSIS
6.2.1 Uses of TREND ANALYSIS
6.2.2 Entering TREND ANALYSIS
6.2.3 Parameter Adjustment During TREND ANALYSIS
6.2.4 Print Operation During TREND ANALYSIS
6.3 DIAGNOSTICS
6.3.1 What does DIAGNOSTICS Do?
6.3.2 Entering DIAGNOSTICS
6.4 PROTECT
6.4.1 Total and Partial Protection
6.4.2 Entering PROTECT
6.5 TIMED PRINTOUT
6.6 DEGAS
6.6.1 The purpose of DEGAS
6.6.2 Problem of Degassing
6.6.3 Entering DEGAS
6.7 ALARM OUTPUT (ANALOGUE OUTPUT)
6.7.1 What Does the Symbol Mean ?
6.7.2 Changing from ALARM to ANALOGUE
6.8 TOTAL DISABLE (TOTAL ENABLE)
6.8.1 Total Disable
6.8.2 Making total pressure measurements - BAR GRAPH
6.8.3 Making total pressure measurements - PEAK SELECT
6.8.4 Notes on Total Pressure measurement
6.9 MULTIPLIER CALIBRATION
6.9.1 What does MULTIPLIER CALIBRATE do?
6.9.2 How does MULTIPLIER CALIBRATE work?
6.9.3 Entering MULTIPLIER CALIBRATE
6.10 MASS SPECTRA
6.10.1 A reference library of MASS SPECTRA
6.10.2 Entering the library
6.10.3 Comparing your results with the library
6.10.4 Selecting the Library
6.11 ANALOGUE DISPLAY
6.11.1 Interpreting ANALOGUE DISPLAY
6.11.2 Entering ANALOGUE DISPLAY
6.12 IEEE ACTIVE (RS 232 ACTIVE)
6.12.1 The RS232 interface
6.12.2 Changing the Baud Rate for RS 232
7. ROUTINE MAINTENANCE
7.1 GENERAL
7.1.1 What needs to be maintained
7.2 CHANGING FILAMENTS
7.2.1 Detecting Filament Burn Out
7.2.2 Preparing to Change Filament #1
7.2.3 Tools and Materials needed
7.2.4 Mechanics of Changing a Filament
7.3 CLEANING THE ION SOURCE
7.3.1 When to Clean the Ion Source
7.3.2 Tools and Materials needed
7.3.3 Disassembly of the Ion Source
7.3.4 Cleaning the Ion Source
7.3.5 Re-assembly of the Ion Source
7.4 CLEANING THE MASS FILTER RODS
7.4.1 When to Clean the Rods
7.4.2 Tools and Materials needed
7.4.3 Cleaning the Analyser
7.4.4 Testing the Analyser
7.5 ADJUSTING THE RF GENERATOR
7.5.1 When to adjust RF Generator
7.5.2 How to adjust RF Generator
8. TROUBLESHOOTING
8.1 POWER
8.2 DISPLAY
8.3 FRONT PANEL
8.4 TOTAL PRESSURE
8.5 SPECTRUM
8.6 FILAMENTS
8.7 MULTIPLIER
8.8 PRINTER
8.9 VOLTAGE CHECKS AND REPAIRS
9. FAIL CODES
9.1 DIAGNOSTICS FAIL CODES
9.2 MULTIPLIER FAIL CODES
10. RS232 INTERFACE
11. IEEE488 INTERFACE
12. ANALOGUE OUTPUT MODULE
SECTION 1
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ORGANISATION OF THE MANUAL
This manual is divided into sections that introduce you progressively to the many features of DATAQUAD. If you read them in the order presented we believe the training to be systematic.
We strongly recommend that you read this manual thoroughly prior to operating the DATAQUAD.
In outline, the Sections contain:
SECTION 2
Unpacking, inspection and installation instructions.
SECTION 3
Quick directions for operating the basic functions of the DATAQUAD. This is not an alternative to reading the manual but a confidence builder to prove you are not reading in vain.
SECTION 4
A comprehensive description of all front panel key pads and rear panel connections. This is a useful reference section until you have sufficient operating experience to ignore it.
SECTION 5
Detailed operating instructions for all available DATAQUAD data collecting modes. Plus hints on when you may choose them and for what applications.
SECTION 6
Descriptions of the operating functions and routines that can be entered by using the INDEX.
SECTION 7
This section introduces the little but necessary routine maintenance that must be done on an RGA.
SECTION 8
A troubleshooting guide.
SECTION 9
Description of DIAGNOSTIC and MULTIPLIER Fault Codes and their probably causes
SECTION 10
Detailed codes and instructions for operating the RS232 Interface to both command and read data from the DATAQUAD
SECTION 11
Detailed codes and instructions for operating the IEEE488 Interface to both command and read data from the DATAQUAD
SECTION 12
Instructions for using the Analogue Output Module accessory.
SECTION 2
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UNPACKING AND INSTALLATION
2.1 UNPACKING AND CHECKING VISUAL DAMAGE
2.1.1.1 When you receive the DATAQUAD, carefully check each item by removing the foam and plastic wrapping to insure that no physical damage has occurred during shipment. Also make sure that all items have been received by checking against the packing note.
CAUTION - DO NOT OPEN THE ALUMINIUM CYLINDER AT THIS STAGE
2.1.1.2 If there has been obvious damage during shipment or if there are items listed on the packing note as shipped which are not in the box, immediately contact your local service representative, or contact:
LARIMAX.
3 Devon Units,
Hatchmoor Industrial Estate,
Torrington,
Devon EX38 7HP
England
Tel: +44 (0) 1805 624728
2.1.1.3 Most insurance claims for shipment damage must be submitted in WRITING within 7 days from the date of delivery so please inspect your DATAQUAD as soon as you receive it.
2.2 BEFORE YOU INSTALL THE MASS FILTER
2.2.1 VACUUM CHAMBER DIMENSIONS
2.2.1.1 The vacuum chamber in which you intend to mount the DATAQUAD analyser must have a 70 mm UHV ("Conflat") flange fitted with a tube of 35mm minimum inner diameter. The distance from the end of the mass filter to its mounting flange is 120 mm (see Figure 2.2.1.1) so, there must be at least that distance free of obstructions inside the vacuum chamber.
2.2.1.2 If your chamber does not have that much room or has the wrong flange, then you will need to use an adaptor. Please contact your Spectramass representative for advice if necessary.
2.2.2. PRESSURES IN SPUTTERING, PLASMA ETCHING, AND CVD SYSTEMS
2.2.2.1 Analysers should not be operated at pressures higher than 1 x 10-4 torr. If you intend to monitor a sputtering or plasma etching process remember that, if the analyser is mounted directly in the chamber, you will not be able to switch on the filaments while at sputtering pressures.
2.2.2.2 CAUTION. A worse problem is that sputtering tends to "throw" material around corners. If the analyser extends into the "throw" area of the sputtering deposition, it will rapidly become coated and cease to function properly. Turning off the power to the DATAQUAD during sputtering or etching will not prevent this contamination and, worst of all:
OUR WARRANTY DOES NOT COVER THE CLEANING OF ANALYSERS.
2.2.2.3 We do, however, supply High Pressure Adapter Kits for just these types of applications so please contact us for assistance.
Figure 2.2.1.1 Analyser with Dimensions
2.3 INSPECTING AND MOUNTING THE ANALYSER.
We urge you to read the whole Section before proceeding.
The analyser is both fragile and very easily contaminated by the slightest touch from your fingers. PLEASE HANDLE THE ANALYSER OUR WAY. Remember that warranty condition in section 2.2.2.2.
2.3.1 REMOVING THE ANALYSER COVER.
2.3.1.1 The analyser is shipped in a double-ended aluminium cylinder for protection (see Figure 2.3.1.1). Hold the analyser by the flange so that the screw slots are facing you.
2.3.1.2 Hold the axis of the cylinder vertical.
2.3.1.3 Undo the two screws and carefully remove the nuts, shakeproof washers and finally the screws. Lift the upper end of the cylinder along its axis trying not to let it touch the analyser.
2.3.1.4 Only hold the analyser at the vacuum flange. Remove the other end of the aluminium cylinder to expose both the feedthrough and the ioniser/quadrupole assembly.
2.3.1.5 If you have to set the analyser down for a moment, place the shorter part of the aluminium cylinder on a firm work surface with the lip uppermost. Put the analyser feedthrough into the cylinder till the flange rests on the lip. DO NOT LEAVE THE ANALYSER IN THIS CONDITION. It can easily tip over and smash if the work surface is knocked. It will also collect dust which may contaminate the analyser.
Figure 2.3.1.1 The Analyser in its Shipping Container
2.3.2 MOUNTING THE ANALYSER TO THE VACUUM CHAMBER
2.3.2.1 The standard 70mm Conflat flange on the analyser can be sealed to the vacuum chamber with either a copper or a Viton gasket. The choice depends on the ultimate pressure you expect in your vacuum system, the copper gasket being the more suitable for UHV work.
2.3.2.2 Take a new gasket, slip it over the quadrupole structure and set it in the grooves of the flange surface.
2.3.2.3 Carefully insert the analyser into the vacuum chamber ensuring that you do not damage the ceramic insulators. Make sure the gasket does not slip part-way out of its slot as you push the two flanges together.
2.3.2.4 If the installation is such that the axis of the analyser is horizontal, rotate the flange until the key-way knob on the centre tube of the feedthrough is as close to the 4 o'clock position as the bolt holes will allow (see Figure 2.3.3.4). This will ensure that the ribbon cable on the RF generator will hang vertically and therefore put less stress on the connector.
2.3.2.5 Bolt the analyser flange to the vacuum chamber flange using the torque appropriate for the gasket material used.
Figure 2.3.3.4 Correct Orientation of Analyser in Chamber
2.4 CONNECTING THE ANALYSER, RF GENERATOR AND CONTROL UNIT.
2.4.1 INSTALLING THE RF GENERATOR
2.4.1.1 The RF Generator is fitted with a cylindrical slotted sleeve that must be aligned with the key welded on the analyser. This will ensure correct mating of the two connectors.
2.4.1.2. When all the pins have engaged in the correct sockets, press the RF Generator firmly onto the analyser assembly to ensure electrical continuity. NOTE: THE LAST 3mm OF MOVEMENT IS ALL IMPORTANT.
2.4.2 ELECTRICAL CONNECTIONS TO THE CONTROL UNIT
2.4.2.1 Make sure that the POWER switch, the red push-button in the upper right-hand corner of the front panel, is in the OFF (out) position. Insert the plug from the RF Generator ribbon cable into the 25 way "D" connector labelled "RF HEAD" at the back of the control unit.
2.4.2.2 Attach the high voltage cable (BNC plug) to the BNC socket labelled "RF HEAD" at the back of the control unit.
2.4.2.3 Attach the power cord to the socket on the back panel of the control unit and connect to a suitable a.c. power supply. 100V, 120V, 220V, 240V ac as indicated on the socket.
2.4.3.3 Ensure that the mains voltage setting, visible above the mains input socket, is correct. If the setting is incorrect, adjust as per section 4.8.8.
SECTION 3
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INITIAL OPERATIONAL CHECK-OUT
The procedure given in this section is designed to check that the DATAQUAD is operating correctly. It ensures that the instrument has arrived in good working order and is installed properly. No attempt is made to describe all the functions or even to explain what we are asking you to do. This is simply an instrument integrity test and confidence builder.
3.1 VACUUM REQUIREMENTS
3.1.1 MAXIMUM PRESSURE
3.1.1.1 Before doing anything else, ensure that the vacuum chamber meets the following minimum pressure requirements. Operating the DATAQUAD at significantly higher pressure will lead to unreliable performance and/or damage to the analyser filaments.
MODEL PRESSURE LESS THAN
________________________________________
DAQ100/DXS 1 x 10 -4 Torr
DAQ100/DXM 1 x 10 -5 Torr
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3.2 CHECK-OUT PROCEDURE
3.2.1 LOCATING THE RIGHT KEYS
3.2.1.1 The explanation of the panel numbers used to identify the keys in this Section is given in Figure 5.0 of Section 5 "MODES OF OPERATION". A quick look at the photograph in this section will help you locate the panels.
3.2.2 CHECKING OUT FARADAY DETECTOR DATAQUADS
3.2.2.1 Press RESET (Panel 4) and hold in while pressing POWER Panel l) on until you hear a "Beep". This indicates that the command has been accepted and the unit is reset to factory memory conditions.
3.2.2.2 If you do not hear the "Beep", switch off the POWER and do this RESET/POWER UP procedure repeatedly until you do hear the "Beep".
3.2.2.3 The monitor will display the message
"PRESS ANY FUNCTION KEY TO START"
"V3.29"
"V3.29" is the current software version and the three digit number specifies the hardware and software configurations.
When contacting SPECTRAMASS or our agent with any technical queries, both the instrument serial number and its "V" state should be quoted. Serial numbers can also be found on RF heads and analysers.
3.2.2.4 Press INDEX (Panel 4)
3.2.2.5 Press DOWN ARROW (Panel 3) to highlight TOTAL DISABLE
3.2.2.6 Press STOP/RUN (Panel 7). Note that TOTAL DISABLE changes to TOTAL ENABLE
3.2.2.7 Press BAR GRAPH (Panel 6).
3.2.2.8 Press DISPLAY SPAN (Panel 6).
b10b3.2.2.9 Press the Down Arrow keys (Panel 3) until the mass axis on the monitor reads "0 - 10".
3.2.2.10 Press PREC (Panel 6).
3.2.2.11 Press the Down Arrow keys (Panel 3) until the "Precision" has a value of "2".
3.2.2.12 Press GAIN/AUTO (Panel 6) once to highlight "GAIN" legend on the monitor (upper left-hand corner). Do not press twice or "GAIN" will have an "A" following it which is not what we want at this stage.
3.2.2.13 Press the Down Arrow keys (Panel 3) and reduce the Gain until it reads "E-05".
3.2.2.14 The scan dot below the mass scale will pass from mass 1 to 10, stop at mass 10 while the the Total Pressure is measured, then it will repeat the scan.
3.2.2.15 The total pressure is shown in the top right corner of the display. It should read "0.0", "E-5A". If this happens, all is well so far.
3.2.2.16 Press FIL #1 (Panel 2). Three things should happen. The display will show "Fil #1 ON", the scan dot will take just a little longer to restart the scan, and the total pressure value will appear in the legend.
3.2.2.17 The filament outgases when it is first turned on and it is quite normal for the total pressure value to rise from its initial measurement.
3.2.2.18 If there is no indication of total pressure consult Section 8 before proceeding.
3.2.2.19 Press DISPLAY SPAN (Panel 6).
3.2.2.20 Press the Up Arrow keys (Panel 3) until the range on the mass axis goes to "0 - 50".
3.2.2.21 Press AUTO/GAIN (Panel 6) to obtain an "A" following the Gain readout.
3.2.2.22 The Gain will autorange until the display shows a bar graph. (see section 5.1.1). Most vacuum systems will give major peaks at mass 18 (H2O) and mass 28 (CO/N2) but there will also be smaller peaks at other masses.
3.2.2.23 If no peaks appear on the monitor consult Section 8.
3.2.3 CHECKING OUT DUAL DETECTOR DATAQUADS
3.2.3.1 Before doing the tests in this section, run your instrument through tests given in Sections 3.2.2.1 to 3.2.2.23 as these are common to all instruments.
3.2.3.2 Note the speed of the scan dot moving across the screen below the mass axis and note the Gain factor.
3.2.3.3 Check the total pressure and wait until it is less than 1 x 105 torr before going to section 3.2.3.4.
3.2.3.4 Press GAIN so that "GAIN" is highlighted but the value is not followed by "A".
3.2.3.5 Use UP ARROW to increase Gain to read "E-9"
3.2.3.6 Press PREC.
3.2.3.7 Use UP ARROW to increase Precision to read "3".
3.2.3.8 Press SEM (Panel 2). Note that the "MULT" indication goes from "OFF" to "ON"
3.2.3.9 Note that the indicated Gain remains the same. Also note that the speed of the scan dot increases.
3.2.3.10 Note that many peaks appear on the display that are roughly the same size with or without the SEM switched on. Check this by switching the MULTIPLIER on and off using the SEM key.
3.2.3.11 If there are no peaks on the display or if the speed of the scan dot has not increased, consult section 8.
3.2.3.12 If your DATAQUAD passed these tests you can be certain that it has been installed correctly and is working satisfactorily.
SECTION 4
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CONTROL KEYS AND THEIR FUNCTIONS
4.0 INTRODUCTION
The DATAQUAD control unit is divided into two sections, the visual display unit (VDU) and the keyboard.
The legend part of the display shows the current operating conditions. They may be changed by selecting the particular parameter with the appropriate function key, then using the UP/DOWN ARROW keys to alter the value. Parameter selection is confirmed by a highlighting cursor which appears on the VDU.
The function keys are split into seven panels numbered 1 to 7 starting with the POWER switch and moving clockwise (see Figure 4.1). In the main, these panels bring together keys that are used to program the DATAQUAD in a particular mode of operation. However, some of the more sophisticated data acquisition modes use function keys from 2 or 3 panels.
This section gives a description of each function key, without showing its application or when you might use it, this information is provided later in the manual.
Figure 4.1 Front Panel of DATAQUAD control unit
4.1 PANEL 1
4.1.1 POWER
4.1.1.1 The main POWER push button is pressed in to switch on
the electronics and is of the self illuminating type. Power is switched off by pressing the button again.
4.2 PANEL 2
4.2.1 FIL #1 and FIL #2
4.2.1.1 The DATAQUAD analyser has two filaments which are used independently. FIL #1 and FIL #2 are ON/OFF toggle keys used to turn on/off the desired filament. If neither filament is switched on and the DATAQUAD is scanning then the display shows the complete word "FILAMENT" and a flashing "OFF". When a filament is selected the display shows the status, either "Fil #1 ON" or "Fil #2 ON".
4.2.1.2 Note both filaments cannot be switched on at the same time.
4.2.1.3 Should a filament fail, the "ON" changes to a flashing "O/C" for the particular filament. If a filament fails under vacuum conditions which are known to be satisfactory, you simply push the key of the spare. You do not have to turn the first one off before selecting the second.
4.2.1.4 If you do not know the vacuum pressure when the first filament failed, you should check it using a separate gauge before switching to the next filament.
4.2.2 SEM (DUAL DETECTOR MODELS ONLY - DATAQUAD DXM)
4.2.2.1 SEM is an ON/OFF toggle key for the high voltage to the Secondary Electron Multiplier. The "ON/OFF" status of the multiplier is shown on the display in the second column. Switching on the multiplier causes the real gain of the system to increase by a factor of 100. To compensate, the attenuation of the electronics is increased - remember it's attenuation - by a factor of 100. The overall effect is to maintain the same "Gain" in partial pressure terms and therefore the same peak heights.
4.2.2.2 The gain of the multiplier can be automatically calibrated using either AUTO/RUN or the MULT CALIBRATION routine from the INDEX.
4.2.2.3 The SEM key is still present on DATAQUAD DXS models but, as you would expect - SEM works only on instruments with Secondary Electron Multipliers fitted.
4.2.3 LEAK DETECT
4.2.3.1 The LEAK DETECT key automatically configures the DATAQUAD for helium leak detection by selecting mass 4 Helium) and setting the display to trend analysis (partial pressure versus time). There is also an audible tone which increases in pitch as the amplitude of the peak increases. This makes leak checking possible even when the monitor is out of sight.
4.3 PANEL 3
4.3.1 ARROW KEYS
4.3.1.1 Arrow Keys do two jobs. They change the value of any highlighted scan parameter and they move the "highlighter" in the INDEX.
4.3.1.2 The arrows that point up increase the value and down arrows decrease the value, but they do not always move the highlighting cursors in these directions.
4.3.1.3 The double arrow moves faster than the single arrow.
4.3.1.4 If you try to move a value beyond its allowed limit, you will hear a "Beep" that is longer than normal, and the highlight will start to flash.
4.4 PANEL 4
4.4.1 INDEX
4.4.1.1 The INDEX key calls up a menu display of additional DATAQUAD options. You select the option you want by using the arrow keys to highlight your choice and then pressing the STOP/RUN key to activate.
4.4.1.2 For some programs you are required to set a time (TREND ANALYSIS and TIMED PRINTOUT) and in others to make another selection within the sub-menu (PROTECT and MASS SPECTRA). Such changes are made with the arrow keys.
4.4.1.3 The following options are so important that we have devoted Section 6 to their complete description:
BAR GRAPH - selection of the optional display modes
TREND ANALYSIS - multichannel peak height vs time
DIAGNOSTICS - self checking of critical voltages
PROTECT - total and partial pressure protection trips
TIMED PRINTOUT - printing after timed interval
DEGAS - degassing of the ion source
ALARM/ANALOGUE OUTPUT - alarm or voltage output
4.4.1.3 (Continued)
TOTAL PRESSURE - total pressure measurement
MULT CALIBRATION - automatic calibration of the SEM MASS SPECTRA - library of standard spectra
ANALOGUE DISPLAY - presentation of peak shapes RS 232 - baud rate selection for the integral computer interface.
4.4.2 TABLE/GRAPH
4.4.2.1 When the DATAQUAD is operating in the PEAK SELECT mode (described in Sections 4.5.1 and 5.2) the TABLE/GRAPH key gives either a tabular or graphical presentation of partial pressure for each channel (selected mass).
4.4.3 PRINT
4.4.3.1 The complete VDU screen display can be printed using the PRINT key (Panel 4). The format is parallel Centronix, Epson graphics and any printer with this capability and graphics software will work. A suitable dot matrix printer is assumed to be present for PRINT options to be functional.
4.4.3.2 The PRINT key cycles the PRINT MODE through three states: "OFF", "SINGLE", and "TIMED".
4.4.3.3 With "OFF" nothing is printed at any time, irrespective of the status of the printer.
4.4.3.4 "SINGLE" causes the displayed data for active (scanning) displays to be copied to the printer at the end of the current scan only. That is, just one print and then the display automatically switches to "OFF". But for non-active displays such as BACKGROUND DISPLAY, STOPPPED, INDEX etc data transfer occurs as soon as PRINT is selected.
4.4.3.5 No data will be acquired during the time the printer is copying the screen.
4.4.3.6 "TIMED" can have either of two effects. If the INTERVAL selected (see below) is less than the time taken to complete a scan then a print is made at the end of each scan. If an interval has been entered that is longer than the time taken to complete a scan then the print is made following the next completed scan after the interval has elapsed.
4.4.3.7 To program the time interval, press INDEX. A menu of options is displayed. Use the arrow key to highlight "TIMED PRINTOUT". Press RUN/STOP. The display on the monitor reads, "PLEASE INPUT INTERVAL TIME". Use the arrow keys to set the desired time interval (in minutes) for the printout. Press BAR GRAPH or other function key to start the acquisition sequence. Timed printout can be aborted at any time, other than during a transfer to the printer, by pressing the PRINT key until "OFF" appears in the PRINT MODE.
4.4.3.8 An important point to remember when using TIMED PRINTOUT is to always set a print interval that is longer than the scan time. If the interval expires during a scan, the legend TIMED PRINTOUT flashes to show you that something is wrong.
4.4.3.9 The message "O/C" for PRINT indicates either that the printer is not connected, not working (perhaps no paper) or that it has not been switched 'On-Line'.
4.4.4 MAX PEAKS
4.4.4.1 Selecting MAX PEAKS causes DATAQUAD to scan the entire mass range to find the eight largest peaks. It then automatically enters the PEAK SELECT mode and loads these 8 largest peaks into the 8 channels in decreasing partial pressure order with the largest in channel 1.
4.4.4.2 When MAX PEAKS is selected the display shows the legend.
"MAXIMUM PEAKS"
"Please Confirm"
You should make sure that the system pressure is low enough for analyser operation.
4.4.4.3 Press MAX PEAKS a second time and the MAX PEAKS routine is started automatically. The DATAQUAD starts at Gain E-05 torr in Faraday (E-07 in multiplier) and scans the complete spectrum at precision code 2, logging any peaks it finds that are larger than a factory set trigger level. At the end of that scan the Gain is increased to E-06 (or E-08) torr and the process repeated. When the instrument has found 8 peaks that exceed its minimum criterion, it changes to a PEAK SELECT display (graphical) and gives the partial pressures, masses and the gain at which each peak was found.
4.4.4.4 The Gain will not be increased above E-09 in Faraday or E-11 torr in SEM, even if 8 peaks have not been found when the maximum gain is reached.
4.4.5 RESET
4.4.5.1 Using the function keys, you can select values for the parameters that affect the acquisition in the PEAK SELECT and BAR GRAPH modes. The RESET key can be used to toggle between the current user defined values and the factory preset values for these parameters.
4.4.5.2 The RESET key is also used in conjunction with the POWER key to turn on the DATAQUAD as described in Section 3 to erase all user-programmed memory.
4.4.6 BGND STORE
4.4.6.1 This key is used to store the background spectrum (Bar Graph), of the residual gases when the system is at the lowest obtainable base pressure. Upto 4 background spectra can be stored.
4.4.6.2 In the BAR GRAPH mode and with the GAIN in manual or auto, pressing BGND STORE displays the legend "STORING BACKGROUND 1". DATAQUAD then runs through a complete spectrum. That is, if the DISPLAY SPAN is less than 100 (or 200), the DATAQUAD scans to the end of the set mass range, detects the short scan, switches to FULL SPAN "ON", and re-scans the entire mass range. In the same way 4 separate backgrounds, identified by numbers 1,2,3 and 4, can be stored. Any stored background spectra can be overwritten by storing a new spectra on top of it.
4.4.6.3 When the "STORING BACKGROUND" legend disappears, DATAQUAD has stored the background bar graph spectrum for subsequent use in background subtraction techniques.
4.4.7 BGND DISPLAY
4.4.7.1 BGND DISPLAY will display each of the four stored background spectra in rotation, each time the key is pressed.
4.4.8 BGND SUB
4.4.8.1 Any of the background spectrum stored in the memory can be automatically subtracted from the current bargraph spectrum by pressing the BGND SUB key. The display shows "BACKGROUND 1(2,3,4) SUBTRACTED" and the data presented is the continuously updated spectrum of the difference between the two.
4.4.8.2 The current bar graph must have the same gain value as that used when the background spectrum was taken otherwise, the command to BGND SUB will be ignored and the display will show " GAIN MISMATCH ."
4.5 PANEL 5
4.5.1 PEAK SELECT
4.5.1.1 PEAK SELECT is one of the main modes of DATAQUAD operation. The display can be presented either as a table or bar chart using the TABLE/GRAPH key described in Sub-Section 4.4.2. Upto sixteen channels (Eight channels enabled at first) are available in table format, each containing one mass peak which can be defined and continuously monitored. The remaining keys of Panel 5 (sections 4.5.2 through 4.5.7) control the selection of parameters associated with the data acquisition in this mode. In the bar chart format upto eight channels can be enabled simultaneously.
4.5.2 CHANL
4.5.2.1 Pressing CHANL highlights the channel number. The arrow keys then move the highlight to the channel in which parameter values are to be modified.
4.5.2.2 Remember that the arrow keys select higher or lower values, they are not always directional in terms of cursor movement.
4.5.3 EN/DIS
4.5.3.1 This is an on/off switch and has several functions.
4.5.3.2 If you wish to monitor more or less channels in PEAK SELECT, EN/DIS toggles to either enable or disable the data acquisition in the highlighted channel.
4.5.3.3 It is also used to enable or disable the overpressure
PROTECT function in both partial pressure and total pressure modes.
4.5.3.4 A third use is to enable/disable the audio tone in LEAK DETECT.
4.5.4 ALARM
4.5.4.1 You can use the ALARM indicator to set a maximum partial pressure limit for each channel monitored in the PEAK SELECT mode.
4.5.4.2 Press the ALARM key once and an arrow appears at the 99% level of the highlighted channel. Pressing ALARM again causes the arrow to disappear.
4.5.4.3 While the ALARM arrow is present and just activated, the arrow keys move the alarm arrow up and down to whatever value you chose.
4.5.4.4 If the height of the peak in that channel exceeds the alarm set-point level, a TTL " High" signal appears on the appropriate pin of a nine-way 'D' connector labelled ALARM OUT on the DATAQUAD's rear panel (see section 4.8.2). If the peak then falls below the ALARM value the signal reverts to a TTL "Low".
4.5.4.5 Note. When the SPECTRAMASS 0-10V Analogue Output Module is in use, the TTL alarm level is not available as this option uses the same 'D' connector on the rear panel.
4.5.5 MASS
4.5.5.1 The MASS key is used in conjunction with the arrow keys (Panel 3) to change the mass in the highlighted channel.
4.5.5.2 If the mass in a particular channel, is set to MASS 0, then that channel will display the Total Pressure.
4.5.6 PREC
4.5.6.1 The PREC key followed by the arrow keys, change the precision code (PC). Increasing the precision code value increases the dwell time at each mass and, therefore, the time required to complete a scan cycle.
4.5.6.2 The precision of the data depends on how much time you can spend averaging it. With DATAQUAD, the number of results that are averaged and the accuracy of the peak search routine, is determined by the PC.
4.5.6.3 For every PC, except PC 0, the DATAQUAD does a peak search through -0.3 to +0.3 amu of the nominal mass position. PC 1 takes only a few fractional mass points for the 0.6 mass range, while PC 4 and 5 both take 16 points.
4.5.6.4 The precision of the data is determined by the number of scans of each 0.6 amu block that are made and averaged before stepping to the next nominal mass block.
Precision Code Number of Scans(Averaged)
__________________________________________________________
PC 0 1
PC 1 2 No.of Scans
PC 2 4 are
PC 3 8 for Faraday detector
PC 4 8 on
PC 5 16 gain range 5
__________________________________________________________
4.5.6.5 In addition to these averages, PC 4 and 5 include an extra "auto zero" step before data is displayed at any mass peak. The instrument steps automatically to mass 5.5 where in normal residual gas analysis there is no 'real' signal. DATAQUAD measures the peak height, which is assumed to be a combination of leakage current in insulators, pre-amp offset, noise, and unfiltered ions. It then subtracts this value from the value of the peak height at the mass being scanned and presents the result as the data point.
4.5.6.6 For PC 1 through 3, the "auto zero" correction is still made but now the subtraction value is only updated at the end of each scan.
4.5.6.7 For PC 0 there is no peak search routine, no averaging, or auto zero. Do not try to quantify anything with PC 0.
4.5.6.8 When choosing a PC for your application these guide lines may help.
Gain Setting Faraday/Multiplier PC
_____________________________________________
E-5 to E-8 F 1 to 3
E-9 and E-10 F 4
E-11 F 5
E-8 to E-11 M 1 to 3
E-12 M 4
E-13 M 5
_____________________________________________
4.5.6.9 There is little or no disadvantage in using a higher value PC at the low gain settings but, if you use a low value of the PC and a high GAIN, you will get odd results.
4.5.6.10 Press PREC (Panel 6). Note that "PRECISION" is highlighted. As you change the value of PREC using the arrow keys, the speed of the scan dot will slow or speed up.
Figure 4.5.6.11 Scans at Diferent Precision Codes
4.5.7 GAIN/AUTO
4.5.7.1 GAIN/AUTO is a toggle key that selects either manual control of gain or autoranging, signified by an "A" after the gain value. In the auto gain mode DATAQUAD software raises or lowers the gain until the largest peak is on-scale. The Up/Down Arrows are used to set gains manually but will not affect the gain when it is set to AUTO.
4.5.7.2 In BAR GRAPH mode the same gain factor is used for the complete scan. In the PEAK SELECT mode, an individual gain factor can be set for each channel using CHANL and the Up/Down keys.
4.6 PANEL 6
4.6.1 BAR GRAPH
4.6.1.1 BAR GRAPH is the second of the DATAQUAD's major modes of data acquisition. Bar graph, gives a partial pressure versus mass, display on the monitor. Other Panel 6 keys (sections 4.6.2 to 4.6.7) allow selection of the parameters associated with this form of data acquisition.
4.6.2 FULL SPAN
4.6.2.1 The DATAQUAD normally scans just the preselected masses that are displayed at the bottom of the BAR GRAPH mass scale. When FULL SPAN is pressed, showing the legend "ON", the DATAQUAD scans the full mass range (100 or 200 mass units).
4.6.2.2 When FULL SPAN is enabled, it appears that there are periods when the instrument is inactive with the scan dot stuck at the end of the display. The DATAQUAD is still scanning however but the acquired data is stored without presentation. FULL SPAN is a toggle key. Pressing it a second time, to display "OFF", will cause the DATAQUAD to return to scanning only the mass range presented on the monitor.
6.2.3 FULL SPAN is used manually as described in sections 4.6.2.1 and 4.6.6.2, and automatically in section 4.4.6.2.
4.6.2.4 A useful application for FULL SPAN is to put the MASS IDENT(IFIER) (See Section 4.6.4) on a mass that is outside the mass range of the display. Normally the partial pressure value of that mass is not registered and the legend shows "-.-". However, with FULL SPAN enabled a partial pressure value will be indicated.
4.6.2.5 When you select STORE BGND with a reduced mass range, the DATAQUAD automatically switches on the FULL SPAN and re-scans the entire spectrum before storing.
4.6.3 DISPLAY SPAN
4.6.3.1 The DISPLAY SPAN key, in conjunction with the arrow keys, sets the mass window to be scanned. Available ranges are 10, 20, 50 and 100 mass units on 100 amu units and 10, 20, 50, 100 and 200 mass units on 200 amu instruments.
4.6.4 MASS IDENT
4.6.4.1 The vertical dotted line that appears in the BAR GRAPH mode is called the mass identifier cursor. It is moved up and down the mass scale by selecting MASS IDENT and using the arrow keys. MASS IDENT can be used to confirm mass numbers and to give partial pressure readings for individual masses. The information is displayed in the "MASS IDENT" and "PART PRESS" columns.
4.6.4.2 The MASS IDENT key has a secondary use in selecting the mass in the Leak Detect mode.
4.6.5 MASS
4.6.5.1 MASS selects the first mass to be scanned in the BAR GRAPH and ANALOGUE DISPLAY modes. The value of the First Mass, "FM" on the display, is changed using the arrow keys.
4.6.6 PREC
4.6.6.1 PREC is used to set the six precision codes which are fully described in Section 4.5.6.
4.6.7 GAIN/AUTO
4.6.7.1 GAIN/AUTO is a toggle key that selects either manual
control of gain or automatic control when the gain value is followed by "A". As in section 4.5.7, in AUTO the largest peak is not allowed to go off-scale if there is a GAIN value that allows it to be on-scale.
4.6.7.2 The uses of GAIN/AUTO in the Bar Graph mode are described in section 5.1.9.
4.7 PANEL 7
4.7.1 AUTO RUN
4.7.1.1 AUTO RUN is intended to help the user who does the same analysis day after day. It automatically starts up, checks and calibrates the instrument before going into BAR GRAPH mode.
4.7.1.2 AUTO RUN takes about 15 minutes.
4.7.1.3 Press AUTO RUN. A message is displayed asking you to confirm that the system pressure is less than that approved for the DATAQUAD.
4.7.1.4 Press AUTO RUN again to start the sequence.
4.7.1.5 Filament #1 is switched on and allowed to warm up for a period so as to allow the filament to outgas and the electronics to stabilise.
4.7.1.6 The diagnostics program is then run to check electronics parameters.
4.7.1.7 The electron multiplier is turned on and calibrated. (dual detector models only).
4.7.1.8 At the end of the AUTO RUN sequence, the DATAQUAD will begin acquiring data in BAR GRAPH mode using the pre- set parameters.
4.7.2 STOP/RUN
4.7.2.1 STOP/RUN has two main uses:-
4.7.2.2 To activate a selection that has been made in the INDEX by highlighting the required option with the Up/Down Arrows.
4.7.2.3 The STOP/RUN key can be used to freeze a current BAR GRAPH display and allow more careful examination or printing. When STOP/RUN is used in this way, the legend "STOPPED" is displayed.
4.8 REAR PANEL
4.8.1 RF HEAD
4.8.1.1. This unit incorporates both RF and DC power supplies together with a pre-amplifier. The RF Head is fitted with a cylindrical slotted sleeve that must be aligned with the key welded onto the side of the analyser. This will ensure correct mating of the two connectors.
4.8.1.2 Adjusting the RF Generator
The RF generator supplied with DATAQUAD has been factory preset so that resolution and mass scale alignment are within specification. The mass alignment is within +-0.3 amu and the resolution between 5 and 10% valley. It will occasionally be necessary to make minor adjustments. For instance, the user may wish to maximise sensitivity if resolution is not critical or if resolution and/or mass scale alignment have drifted due to analyser contamination.
4.8.1.3 How to Adjust the RF Generator
1. Before making any adjustments to the RF generator/ analyser combination, the DATAQUAD should be thoroughly warmed up for 1 hour.
2. Select ANALOGUE DISPLAY mode
3. Check that the mass scale alignment is within specification, that is +-0.3 amu
4. The mass scale is aligned so that the centroid of a particular peak corresponds to the displayed numbers. This has to be done at both the high and low ends of the mass spectrum. The MAIN MASS ALIGN adjusts the whole spectrum equally and the LOW MASS ALIGN adjusts the low end of the spectrum (see Fig.4.8.1.1)
5. Select the water group peaks, 17 and 18 amu and adjust the LOW MASS ALIGN trimpot until the centroid of the mass 18 peak is vertically above the 18 mass marker.
6. Select the highest known mass peak in your spectrum. On DAQ 100 versions the peak should be between 90 and 100 amu and on DAQ 200 between 190 and 200 amu. Adjust the MAIN MASS ALIGN trimpot until the centroid of the peak is above the appropriate mass marker.
7. As the two trimpots are interactive it will be necessary to repeat the above procedure until both low and high masses ate aligned correctly.
8. The resolution of the RF generator is adjusted in a similar way and the MAIN RESOLUTION and the LOW MASS RESOLUTION adjustments are also interactive.
9. Select the water group peaks, 17 and 18 and adjust the LOW MASS RESOLUTION trimpot until the valley between the two masses is 10% of the mean peak heights.
10. Using a suitable sample scan a group of peaks near the maximum mass of the DATAQUAD and adjust the MAIN RESOLUTION trimpot until a 10% valley resolution is achieved.
11. Repeat steps 9 and 10 until the resolution is 10% valley throughout the mass range.
_____________________________________
(a) (b)
o o
(c)
o
(d)
o
_____________________________________
(a) Main Resolution trimpot (c) Main Mass Alignment
(b) Low Mass Resolution trimpot (d) Low Mass Alignment
Fig.4.8.1.1
4.8.2 ALARM OUT
4.8.2.1 A 9 way "D" type socket is provided which supplies TTL outputs, one per channel, for the first 8 channels in peak select mode. High or low signals indicate if the partial pressures are above or below the preset alarm levels.
4.8.3 PRINTER
4.8.3.1 DATAQUAD uses a 37 way "D" type printer socket
4.8.3.2 Printer Pin Outputs From DATAQUAD
A circuit diagram of the interface card and printer socket of the DATAQUAD can be found at the end of the manual. The printer, which is attached to Plug 2 on the interface card, should have a Centronics type parallel interface. A description of the pin assignments and respective interface signals are given below:
Pin Signal Direction Description
1 Strobe Out Strobe pulse sends data out.The pulse width from the emitter is more than 0.5microseconds
2 Data 1 Out These signals represent inf-
3 Data 2 Out ormation on the 1st to 8th
4 Data 3 Out bits of parallel data. Each
5 Data 4 Out signal is at high level when
6 Data 5 Out the data is logical 1 and
7 Data 6 Out low when it is logical 0.
8 Data 7 Out
9 Data 8 Out
10 Acknowledge In Approx. 2 microsecond pulse.A low signal level indicates all data has been received and therefore more data can be sent from the DATAQUAD.
11 P.Busy In A high signal on the line causes the DATAQUAD not to send data.
16 0 V - Logic ground level
19-30 0 V - Twisted pair return signal ground level.
31 Init. Out A high 50 microsecond signal is used for initialisation of data transfer.
33 0 V - Same as 19-30
______________________________________________________
Notes:
a) The direction refers to the direction of signal from the DATAQUAD.
b) Return denotes a twisted pair return which is connected to signal ground level. For interface wiring be sure to use a twisted pair cable for each signal and to complete the connection on the return side. To prevent noise these cables should be shielded and connected to the DATAQUAD chassis.
c) Interface conditions are based on TTL level. The rise and fall times of each signal is less than 0.2 microseconds.
4.8.4 AUX I/O
4.8.4.1 This is a 9 way "D" type socket the pins of which carry + and - 15 volt supplies and four logic lines derived from a digital input/output port. The AUX I/O socket is used in conjunction with other connectors to provide power and signals for optional extension modules such as the Analogue Output Module and the IEEE/488 interface.
4.8.5 VOL
4.8.5.1 This potentiometer may be adjusted to alter the speaker volume, a facility particularly useful when using the DATAQUAD in leak detect mode.
4.8.6 VIDEO
4.8.6.1 This is a minature phono socket carrying a 1 volt p-p composite video output which may be used for connection of an external monochrome monitor.
4.8.7 EXPANSION BUS
4.8.7.1 This is a 37 way "D" type socket which carries the microprocesor address data buses and most control signals, and is used in conjunction with the IEEE/488 extension module.
4.8.8 LINE CORD CONNECTION AND FUSES
4.8.8.1 The power supply connection is made via a three pin IEC plug on the rear chasis using the cable provided. In certain countries the line cord will be equipped with a plug conforming to local standards but if your instrument requires a plug to be fitted the connections are as follows:
Live - Brown
Neutral - Blue
Earth/Ground - Green/Yellow
The Earth wire MUST be connected to an efficient power supply Earth for safety.
4.8.8.2 The power supply tapping is normally factory set to suit the local supply but it may be changed to suit your requirements as follows. Unplug the power supply cord then, using a small screwdriver, prise open the hinged selector cover which is part of the power supply socket. Remove the selector drum and rotate it so that the desired voltage setting is facing towards you. Replace the drum and reclose the hinged cover.
4.8.8.3 A fuse is fitted into the live input and should be rated as follows:
Power Supply Fuse Rating
___________________________________________________
100 volts 1.6 amps ANTI-SURGE
120 volts 1.25 amps ANTI-SURGE
220 volts 600 milliamps ANTI-SURGE
240 volts 600 milliamps ANTI-SURGE
____________________________________________________
The DATAQUAD is designed to operate on both 50 and 60 Hz AC power supplies without adjustment
4.8.9 RS232 INTERFACE
4.8.9.1 An integral RS232 interface is fitted which requires a 25 way "D" type connector. The operation of the interface is described in Section 10
SECTION 5
________________________________________________________________
MODES OF OPERATION
This section is a step by step operating guide for DATAQUAD with V3 software. If you have read the manual in the order it was presented, Section 4 has made you familiar with the uses of the function keys.
If you follow the instructions in this section, you will be introduced to all the features of DATAQUAD and will obtain displays similar to the examples given although the peak heights and masses will certainly differ from ours.
Remember in Section 4 we assigned an arbitrary panel numbering scheme to the function keys. Panel 1 starts at the block with the POWER switch and moves clockwise from there (See figure 5.0).
Figure 5.0 Panel Numbering
5.1 BAR GRAPH
DATAQUAD has extensive bar graph facilities which are available in sub-menus selected via INDEX in the normal way. BAR GRAPH MODE is the first INDEX entry and when activated, by pressing the RUN/STOP key, the BAR GRAPH MODE sub-menu is displayed which contains four entries as follows:
SINGLE SCREEN
SPLIT SCREEN
LOG/LOG
LOG/LIN
The required mode may be selected by using the arrow keys and either the RUN/STOP or BAR GRAPH key. Since many aspects of the four bar graph modes are similar we will first look at single screen bar graph before going on to the extra features of the other three modes.
5.1.1 WHAT IS A BAR GRAPH?
5.1.1.1 A BAR GRAPH is a display of partial pressure versus mass. The partial pressure is proportional to the ion current for each mass and so is a quantitative picture of the components that are in the system. All peak shape information is ignored and the amplitudes, or partial pressures, are presented as vertical lines directly above the mass number.
5.1.2 WHEN DO YOU USE A BAR GRAPH?
A BAR GRAPH is useful in many circumstances:
5.1.2.1 When you wish to survey the background or residual gases in the chamber to see what the major constituents are.
5.1.2.2 If you are collecting data on more than the sixteen components allowed in the Peak Select mode.
5.1.2.3 If you do not know what to expect from your vacuum and so cannot preselect masses.
5.1.2.4 The vacuum chamber is causing you problems and it may be contamination due to an air leak, a water leak, hydrocarbons backstreaming from a pump, hydrogen that is not being removed by a cryopump, etc., etc.
5.1.2.5. Figure 5.1.2.5 shows an example of the display obtained in the BAR GRAPH mode.
Figure 5.1.2.5 Typical Bar Graph Display.
5.1.3 GETTING STARTED
Enter the BAR GRAPH mode as follows:
5.1.3.1 Press POWER (Panel l).
5.1.3.2 When the display shows the logo "PRESS ANY FUNCTION KEY", press BAR GRAPH (Panel 6).
5.1.3.3 Make sure that the vacuum chamber pressure is less than 5 x 10-5 torr before continuing. Operating the DATAQUAD at a significantly higher pressure can lead to unreliable performance, damage to the analyser, and/or premature filament failure.
5.1.3.4 If the DATAQUAD has been reset the GAIN will indicate "E-5A" and the PRECISION will show "3". The Total Pressure will not show in the top right corner of the display. The scan dot will go across the display under the mass scale.
5.1.3.5 To turn on the TOTAL PRESSURE reading, press INDEX, use the Down Arrow to highlight TOTAL DISABLE, press STOP/RUN and note that it changes to TOTAL ENABLE.
5.1.3.6 Press BAR GRAPH and note the numbers at the top right hand side of the display.
5.1.3.7 Turn on the filament by pressing FIL #1. The display reads "FIL #1 ON". At the end of the next scan, the TOTAL PRESSURE will display your system pressure.
5.1.3.8 The GAIN will change to indicate "E-6A" or "E-7A" depending on the peak heights of the components in the system, eventually the scan will repeat many times without changing. The spectrum should look something like Figure 5.1.2.5.
5.1.3.9. Notice that the indicated total pressure rises when the filament is first turned on as the filament and ion source outgas.
5.1.4 CHANGING THE MASS RANGE
5.1.4.1 DISPLAY SPAN (panel 6) varies the mass range, or size of the mass window, plotted on the x-axis of the BAR GRAPH. The possible ranges are 10, 20, 50 and 100 mass units for a 100 mass range instrument, and the additional 200 mass units for the 200 mass range instrument.
5.1.4.2 Press DISPLAY SPAN and note that the "DISP SPAN" (right hand column of the legend on the monitor) is highlighted. Press the arrow keys (Panel 3) to change the window. If you try to command a value that is out of range, a longer than normal "Beep" will sound.
5.1.4.3 The new range is instantly displayed on the monitor but it may take the completion of one more scan before the scan dot and peak update will coincide.
5.1.5 CHANGING THE MASS AT WHICH THE SCAN STARTS
5.1.5.1 The first mass of the BAR GRAPH is selected by pressing the MASS key (Panel 6) and the arrow keys. The mass scale will shift on the x-axis as you change the first mass (FM).
5.1.5.2 The mass range and the starting mass of the displayed scan is controlled therefore by combining DISPLAY SPAN and MASS. For example, if the first mass is 9 and DISPLAY SPAN is 20, a mass range of 9 - 29 mass units will be plotted. Changing MASS to 7 will select a mass range of 7 - 27. Changing DISPLAY SPAN to 50 will command a mass range of 7 - 57.
5.1.6 SCANNING THE FULL SPAN BUT DISPLAYING LESS
5.1.6.1 FULL SPAN (panel 6) is a toggle key that alternates between "ON" and "OFF". The status is indicated on the right side of the display legend and when "ON", the DATAQUAD scans and stores the full mass range no matter what MASS and DISPLAY SPAN is selected.
5.1.6.2 Choose a DISPLAY SPAN of "20" and a First Mass of "12". Your display should look like figure 5.1.6.2. There are periods of time when the DATAQUAD is apparently inactive. That is, the scan dot will be stationary at either end of the mass scale and no data updates will be plotted. In fact, the DATAQUAD is still scanning but the data being acquired is outside the mass range displayed.
Figure 5.1.6.2
5.1.6.3 Now look at the "MASS IDENT" on the display, it probably still reads "50" which is the default position but the "PART PRESS" will no longer show "-.-" but will indicate a value. Even though the cursor is not visible, the DATAQUAD is scanning over its mass position and the partial pressure is being recorded.
5.1.6.4 This is useful if you want to look closely at a short mass range but must keep an eye on some gas outside the displayed mass window.
5.1.6.5 The major uses for FULL SPAN, however, are more subtle and not user selectable. FULL SPAN is automatically switched "ON" if you request BACKGROUND STORE or MAX PEAKS. In either program the computer assumes you want to store the complete spectrum, not just the piece that is currently displayed.
5.1.7 SCAN SPEED AND PRECISION OF RESULTS
5.1.7.1 The PREC(ISION CODE), at first glance, controls the scan time. Increasing the precision code (PC) value increases the dwell time at each mass and therefore the time required to complete a scan cycle. But, the effects of a larger PC value are much more important than simply slowing down the scan rate. A higher value of PC increases the precision of the mass search, the precision of the results and reduces system noise. (See Section 4.5.6.
5.1.7.2 The precision of the data depends on how much time is spent averaging it. With DATAQUAD the number of results that are averaged and the accuracy of the peak search routine is determined by selecting a precision code value.
5.1.7.3 Increasing the PC increases the dwell time at each mass and therefore the time required to complete a scan cycle. However, a higher PC value increases the accuracy of the results and reduces signal noise.
5.1.7.4 For PC's 3, 4 and 5, the DATAQUAD does a peak search through - 0.3 to + 0.3 amu of the nominal mass position.
5.1.7.5 The precision of the data is determined by the number of measurements taken at each point in the 1 amu (or less) block, and this will vary with both the precision code and the gain:
Precision Code No.of Measurements per Point
Lowest Gain Highest Gain
_______________________________________________
PC 0 1 64
PC 1 2 64
PC 2 4 256
PC 3 8 256
PC 4 8 512
PC 5 16 1024
_______________________________________________
5.1.7.6 In addition to these "on-the fly" averages, DATAQUAD has an extra auto zero step before data is displayed. The instrument automatically steps to mass 5.5 where there is normally no genuine signal, measures this value and it is assumed that this is a combination of leakage current in the insulators, pre-amp offset, noise and unfiltered ions. The value measured at 5.5 is then subtracted from the peak height measured at each mass.
5.1.7.7 For PC1 and 2 the auto zero correction is still made but less frequently.
5.1.7.8 For PC 0 there is almost no peak search routine, little or no averaging or auto zero and it is only intended for use as a quick overview of vacuum conditions. PC 0 should never be used for quantification.
5.1.7.9 The following guidelines may help in choosing an optimum PC to work with :
Gain Setting Faraday/Multiplier PC
_____________________________________________
E-5 to E-8 F 1 to 3
E-9 and E-10 F 4
E-11 F 5
E-7 to E-11 M 1 to 3
E-12 M 4
E-13 M 5
_____________________________________________
5.1.7.10 There is no advantage in using a higher PC value at low gain settings and if you use a low value of the PC and a high gain you will get confusing results.
5.1.7.11 Press PREC (Panel 6) and note that "PRECISION" is highlighted. As you change the value of PREC using the arrows keys, the speed of the scan dot will slow or speed up.
5.1.7.12 The differences in scan speed between PC 1 and 5 may not be great but repeated scans will show much greater variation on PC 1 than PC 5 and some peak heights may vary very significantly.
5.1.8 IDENTIFYING MASSES AND MEASURING PARTIAL PRESSURES
5.1.8.1 The partial pressure of a single selected peak can be displayed on the monitor using the MASS IDENT key and the arrow keys to move the cursor, a vertical dotted line, to the mass peak of interest. The mass selected is listed along with its partial pressure on the left side of the monitor legend.
5.1.8.2 The MASS IDENT is particularly useful to identify individual peaks on the 200 mass range. With smaller mass ranges the peaks can often be interpreted from interpolation of the mass scale.
5.1.9 GAIN AND SENSITIVITY
5.1.9.1 The GAIN setting alters the sensitivity of the analyser and the amplitude of the peaks. Unfortunately, even though the word GAIN is correct for this context, it can cause some confusion. As you expect, if you increase the sensitivity of DATAQUAD, the small peaks get bigger and the big peaks overload. DATAQUAD measures peak heights as pressures and the gain factor is the exponent of the pressure in torr. That is, if you measure 2.5 on the 'y' axis to the top of a peak and the GAIN reads "E-7", the partial pressure of that component is 2.5 x 10 -7 torr.
5.1.9.2 If you now wish to amplify that peak to see something smaller you must change the GAIN value to "E-8". That is, you make the GAIN value smaller since 10-8 is smaller than 10-7. The easiest way to deal with this confusion is to remember only that 8 is bigger than 7 so, of course the peaks will be bigger when you switch to "E-8".
5.1.9.3 To manually change the value of the GAIN, you must first toggle the GAIN key until the highlighted display shows no letter "A" after the exponent say, "E-8". Then use the arrow keys to select the sensitivity you need.
5.1.9.4. The GAIN value is controlled automatically when you toggle the GAIN key until the symbol "A" appears after the value. In automatic operation, the gain value changes so that the largest peak is not greater than 95% of full scale.
5.1.9.5 Note, under some circumstances 5.1.9.4 cannot be correct. For example, if a peak height exceeds full scale on "E-7A" GAIN and the multiplier is on, the lowest value for GAIN is 10-7 torr. The auto gain cannot switch any lower so the peak will go to the 10 level on the y axis.
5.1.10 DISPLAYING TOTAL PRESSURE
5.1.10.1 When you first switch on in the Bar Graph mode, the Total Pressure which is normally displayed in the top right hand corner of the screen will not be there. There are technical reasons for not having the display on at all times.
5.1.10.2 In BAR GRAPH mode the Total Pressure is switched on by selecting the INDEX and highlighting TOTAL DISABLE, then pressing the STOP/RUN key. The legend then reads "TOTAL ENABLE". Going back to BAR GRAPH will show a display in the upper right hand corner of the screen.
5.1.10.3 In PEAK SELECT mode the Total Pressure is selected by setting to Mass "0". This is done by selecting the required channel using the CHANL and arrow keys to move the highlight. Then press MASS and use the Down Arrow until the mass reaches "0". Note that Faraday collector and AUTOGAIN are automatically selected. Normally the first or last channels are used for Total Pressure measurement but any channel can be selected for this purpose.
5.1.11 BACKGROUND STORING, DISPLAYING AND SUBTRACTING
In all vacuum systems there is 'Background' pressure which cannot be removed. Even in the most tightly sealed chamber the vacuum pumps will never remove every gaseous molecule. The walls of the system have absorbed gas which slowly desorb into the vapour phase and into the system.
5.1.11.1 To avoid confusing the "sample" i.e. what you want to see, with the "background" i.e. what you do not want to see, DATAQUAD allows you to store the Bar Graph background into memory by pressing the BGND STORE key (Panel 4). A title appears that states "STORING BACKGROUND NUMBER 1". After the current scan is finished, FULL SPAN is turned "ON" and the next complete spectrum is saved. The title then disappears and the DATAQUAD resumes normal scanning. DATAQUAD can store upto 4 background spectra in this way.
5.1.11.2 The BACKGROUND software will operate with the GAIN set to manual or auto.
5.1.11.3 To display the BACKGROUND spectrum at any time use key BGND DISPLAY. This interrupts the current Bar Graph scan and shows the background with the highlighted title "BACKGROUND NUMBER 1". To recover from this condition, press BAR GRAPH again.
5.1.11.4 If you press BGND DISPLAY before you have stored a background, you will find that a random pattern of full scale peaks appear. This is the best way we can remind you that you have not stored one.
5.1.11.5 To subtract the background from the current spectrum, press BGND SUB. If you do it correctly the title reads "BACKGROUND NUMBER 1 SUBTRACTED" but if you do it wrong nothing happens! The essential point is that the GAIN of the current bar graph must be the same as the GAIN at which the background was taken. Clearly, it would be very confusing if you subtracted peak heights of a background measured at a gain of E-9 torr from a sample spectrum done at E-6 torr. The background would have an effect 1000 times greater than reality.
5.1.11.6 If you perform a BGND STORE followed immediately by a BGND SUB, the signals will go to zero. That is, the bar graph displayed on the monitor will have nearly zero intensity across the mass range. This is reasonable since you will be subtracting two very similar spectra.
5.1.11.7 What if the background spectrum has some peaks that exceed full scale? The subtraction circuit notes that an overloaded memory exists but it cannot distinguish between a 2% overload or a 200% overload and so it does nothing. When you subtract the background and the display shows "BACKGROUND NUMBER 1 SUBTRACTED', it simply leaves the overloaded peaks as an indication of some special circumstance.
5.1.11.8 DATAQUAD has the ability to store upto 4 background spectra. To get to other memory positions so as to make use of the multiple stores, use the BGND DISPLAY key to toggle through the available BACKGROUND NUMBER's. Return to BAR GRAPH, set up the data collection parameters as you want them, then press STORE BGND. That particular background will be stored in the location you last called up with the BGND DISPLAY key.
5.1.12 SPLIT SCREEN
Activation of the SPLIT SCREEN mode of operation results in the display of two sets of bar graph axes. The on-line sample spectrum will be displayed on the upper axis while the lower axis is used for display of the currently displayed spectrum from the library or one of the four backgrounds.
The operation of the upper half of the display is exactly the same as in single screen bar graph except that the vertical display resolution is halved and the PREC and GAIN entries now relate to both upper and lower spectra, with the upper precision and gain being given first together with the detector type, e.g:
PRECISION. . .0/2
GAIN..........F05/M11A
This display means that the upper spectra is obtained using the Faraday detector, on precision code 0 and manual gain 5, while the lower is with the SEM on precision code 2 and auto-gain on 11.
Whenever the split screen mode is entered, the arrow keys may be used to step through the mass spectral library entries and the four user backgrounds which are displayed on the bottom half of the screen while the current spectrum can be "ON-LINE" or "STOPPED". In this way it is possible to make visual comparisons of the two spectra under either condition.
5.1.12.1 A LIBRARY SEARCH may be requested in the split screen mode by moving the MASS IDENT cursor to the mass of interest and then pressing the AUTO RUN key.
5.1.12.2 When a LIBRARY SEARCH is activated, the on-line spectrum is put into a STOPPED state while the search is performed. At the end of the search the number of spectra found in the currently selected mass spectral library (Chemical or Semiconductor) containing the target mass is displayed and the first spectrum found is displayed. The arrow keys can used to step through the other spectra found.
5.1.12.3 If as a result of requesting a LIBRARY SEARCH, no spectrum is found with the target mass included, the mesage "0 FOUND" is displayed and normal operation is resumed.
5.1.12.4 BACKGROUNDS may be displayed in two ways in SPLIT SCREEN mode, by pressing the BGND DISPLAY key or by using the arrow keys to step through the mass spectral library which includes the four stored backgrounds at the end of the currently selected library file.
5.1.12.5 The BGND STORE key has the same function during SPLIT SCREEN bar graph display except that the lower spectrum being displayed at the time BGND STORE is pressed will be updated by the stored spectrum. Note: make sure that the spectrum to be overwritten by the new BGND STORE command is one that is no longer wanted.
5.1.12.6 The BGND SUB key is used in the same way as in single screen bar graph except that if the background and online spectra have different gains then the message "GAIN MISMATCH" is displayed at the top of the VDU screen and a short "Beep" is emitted by DATAQUAD.
5.1.13 LOG/LOG and LOG/LIN BAR GRAPH MODES
Both of these modes perform a bar graph scan with autoranging over three decades of gain.
5.1.13.1 For the LOG/LOG mode, the partial pressures within each decade are logarithmic to the base 10 with the y-axis graduations indicating a scaling of 1-3-5-7-9.
5.1.13.2 The LOG/LIN mode has a linear scaling between decades and a scaling of 2-4-6-8-10.
5.1.13.3 Autorange operation is selected by pressing the GAIN/AUTO key twice and is indicated by an "A" adjacent to the the GAIN display at the top of the screen.
5.1.13.4 When autorange is selected the three decade gain range will be automatically adjusted up or down so as to bring all of the peaks on scale.
5.1.13.5 Note: Background Display/Store/Subtract are not operational in either log display mode.
5.1.13.6 When the MASS IDENT cursor is used in either log display mode, the partial pressure displayed at the PART PRESS position on the screen is that of the mass at the cursor position together with the relevant gain.
5.1.14 RESETTING EVERYTHING TO PRE-SET (ie DEFAULT) VALUES
5.1.14.1 Sections 5.1.1 through 5.1.13 have described how the bar graph display can be changed by the front panel keys. The parameters that you set are stored in the DATAQUAD's volatile memory. The RESET key can be used to toggle between the display obtained with your set values and the factory preset values.
5.1.14.2 Pressing the RESET key and holding it in while switching on the POWER erases all of the user set parameters from the DATAQUAD memory for all modes. This is useful for removing any glitches that appear in the software. A "POWER-UP RESET" will return any other bar graph mode to the single screen option.
5.1.15 USING THE ELECTRON MULTIPLIER ON DXM MODELS
Ensure that the vacuum system pressure is well below 1 x 10-5 torr before switching on the secondary electron multiplier collector by pressing the SEM key.
5.1.15.1 For models with a dual detection system, switching on the electron multiplier will cause an increase in the sensitivity of approximately 100 times. Very small peaks that cannot be detected with the Faraday cup detector can now be seen.
5.1.15.2 Another advantage of the multiplier is that you can choose to ignore the sensitivity increase and instead use the same gain factor as that used for the Faraday scan. The technical difference is that in doing this a smaller feedback resistor is used in the pre-amplifier and this has a smaller time constant leading to higher scan speeds at the same precision.
5.1.15.3 SEM (Panel 2) is an on/off toggle key for power to the secondary electron multiplier. The "ON/OFF" status of the multiplier is displayed in the upper right hand corner of the monitor. Note that the speed of the scan increases, the scan dot goes quicker, with the multiplier "ON".
5.1.15.4 In BAR GRAPH, if you have the TOTAL PRESSURE enabled (see section 6.8.2), the scan dot will apparently hesitate at the end of the scan. The SEM is turned OFF before the total pressure is measured and the slow decay of the EHT means that the DATAQUAD scan must be slowed down.
5.1.15.5 The GAIN/AUTO key will operate with the multiplier on as described in Section 4.7.7
5.1.16 PRINTING OUT RESULTS
5.1.16.1 The complete monitor display can be printed using the PRINT key (Panel 4). The format is parallel Centronix and any printer with this capability and suitable graphics software will work. The presence of a suitable printer is assumed for these instructions.
5.1.16.2 The PRINT key cycles the PRINT MODE through three states: "OFF", "SINGLE", and "TIMED".
5.1.16.3 With "OFF" nothing is printed at any time, independent of the status of the printer.
5.1.16.4 "SINGLE" causes the data from the active display, to be copied to the printer at the end of the current scan. Therefore only one print is obtained before the display automatically switches to "OFF". For static displays such as BACKGROUND SUBTRACT, data transfer occurs as soon as PRINT is selected.
5.1.16.5 Note: No data will be acquired during the time the printer is copying the screen.
5.1.16.6 TIMED can have either of two effects. If the INTERVAL
(see below) is less than the scan cycle then a fresh print is made at the end of every completed scan. If an interval has been entered that is longer than the scan cycle then a screen print will occur after the completion of the scan in progress after the interval has elapsed.
5.1.16.7 To program the time interval, press INDEX. A menu of options is displayed. Use the Arrow key to highlight TIMED PRINTOUT. Press STOP/RUN. The display on the monitor reads, "PLEASE INPUT INTERVAL TIME". Use the arrow keys to enter the desired time interval in minutes. Press BAR GRAPH or other function key to start the acquisition sequence. TIMED PRINTOUT can be aborted at any time, other than during a transfer to the printer, by pressing the PRINT key until "OFF" appears in the PRINT MODE.
5.1.16.8 An "O/C" message for PRINT indicates either that the printer is not connected correctly or that it has not been switched "On-Line" at the end of a scan.
5.2 PEAK SELECT
5.2.1 WHAT IS PEAK SELECT?
5.2.1.1 PEAK SELECT is an alternative method of displaying mass information. Instead of looking at the complete mass range as in Bar Graph, a few selected masses are displayed either in a table format or graphically as a collection of histograms.
5.2.2 WHEN DO YOU USE PEAK SELECT?
5.2.2.1 Peak Select is most useful when you have identified the gases that are important to you maybe after using Bar Graph. Up to 16 peaks can be displayed as a table of partial pressures versus mass but only the first 8 peaks can be displayed in the graphical form.
5.2.2.2 PEAK SELECT measures only those peaks that are important to your application and no time is wasted scanning over blank areas or those components that are of no interest to you.
5.2.2.3 Mass selection for PEAK SELECT can be made in three ways, factory preset, user preset, and MAX PEAKS. All are described in this section.
Fig.5.2.2.1 Peak Select - Graphical
Fig.5.2.2.1. Peak Select - Table
5.2.3 GETTING STARTED
5.2.3.1 If the DATAQUAD has POWER on, press PEAK SELECT (Panel5) and skip to Section 5.2.4.
5.2.3.2 If DATAQUAD is off, press and hold in the RESET (Panel 4) while you press POWER (Panel l). You will hear a "Beep" indicating that the RESET/POWER UP command has been taken.
5.2.3.3 Press PEAK SELECT (Panel 5). The table format appears with the factory preset masses 2, 18, 28, 32, 40, 43, 44,and 55.
5.2.3.4 Before turning on the filament make sure that the vacuum chamber pressure is less than 1 x 10-4 torr. Press FIL #1. The table fills with the peak amplitudes and GAIN factors. Note that the GAIN for each channel is in auto ranging mode and an "A" appears after the GAIN value.
5.2.3.5 Press TABLE/GRAPH (panel 4). Note that the format changes to graphical form but that the information is identical to the table format.
5.2.4 CHANGING THE MASS TO WHICH A CHANNEL IS PROGRAMMED
5.2.4.1 CHANL and MASS together select the masses that are loaded into the eight channels for graphical mode and 16 in the case of table format.
5.2.4.2 Press CHANL (Panel 5). The arrow keys move the channel highlight and select the channel in which the mass is to be changed.
5.2.4.3 Press MASS (Panel 5). Use the arrow keys to change the mass for that channel.
5.2.5 TEMPORARILY SKIPPING SOME CHANNELS
5.2.5.1 If you need information on less masses, disable the channels not required. This speeds up the sampling rate for the remaining channels. To disable a channel, press CHANL and use the arrow keys until the desired channel is highlighted. Then press EN/DIS (Panel 5) to disable that channel. The mass and gain to which that channel is programmed remains visible and can be changed even though it is not enabled.
5.2.5.2 To enable a disabled channel, use the CHANL and arrow keys to select the desired channel. Press EN/DIS.
5.2.5.3 Note that channels 9 to 16 are disabled on initial power up but may be enabled by following the above procedure.
5.2.6 ALARM LEVELS.
5.2.6.1 DATAQUAD has ALARM outputs as standard and optional ANALOGUE outputs. Check that ALARM outputs are selected by pressing INDEX. Towards the bottom of the list it will say either ALARM OUTPUT or ANALOGUE OUTPUT. If ALARM is selected then press PEAK SELECT. If it is ANALOGUE, then use the arrow keys to highlight ANALOGUE OUTPUT and press the STOP/RUN key. ALARM OUTPUT should now be displayed. Press PEAK SELECT to return. For a full explanation of ALARM/ANALOGUE outputs see section 6.11.
5.2.6.2 Press ALARM. If you are in TABLE mode the ALARM column for the highlighted channel will change from OFF to ON and vica versa if you press ALARM again. In GRAPH mode an arrow will appear at the top, "9.9" position of the highlighted channel. Use the arrow keys to move the alarm arrow to desired position on the scale. You can toggle to TABLE to see the actual alarm value entered.
5.2.6.3 The ALARM provides a TTL signal which appears on the 9-pin "D" socket on the rear panel labelled "ALARM OUTPUT". The common line is pin 9 and the channel 1 signal appears as a High/Low on pin 1 with respect to pin 9. Other channels are correspondingly numbered. When the arrow is below the alarm set point the TTL level is low. When the arrow is above the alarm level the output is high. The signals can be used to trigger some external audio or visual signal when a peak height reaches a critical value. It is not intended to substitute for a continuous voltage signal necessary for process control, this is provided by the Analogue Output Module.
5.2.7 SCAN TIME AND PRECISION OF RESULTS
5.2.7.1 The time taken to measure each partial pressure depends on the precision code selected together with the gain settings. A discussion of this interrelationship can be found in Section 4.5.6.
5.2.7.2 The channels can have individual GAINS but cannot be set to individual PRECISIONS. It is therefore advisable to use a precision appropriate to the highest GAIN factor.
5.2.8 GAIN AND SENSITIVITY
5.2.8.1 The GAIN can be set individually for each channel in the peak select mode either manually or automatically.
5.2.8.2 GAIN/AUTO is a toggle key that selects either manual or automatic ("A" follows GAIN value) control of gain.
5.2.8.3 For manual operation, press CHANL and use the arrow keys to select the channel. Then press GAIN/AUTO (Panel 5) until "A" disappears, and use the arrow keys again to adjust the gain to the desired value.
5.2.8.4 For automatic gain control, press GAIN/AUTO until "A" appears. The DATAQUAD will automatically adjust the gain for each channel so as to obtain a suitable partial pressure scaling.
5.2.8.5 There are two circumstances in which the GAIN of all channels will be "A" when peak select is entered:
a) If the bargraph GAIN shows "A" when you enter MAX PEAKS.
b) If PEAK SELECT is chosen with the factory set parameters.
The latter is accomplished when PEAK SELECT is pressed for the
first time after a RESET/POWER UP, or by pressing RESET at any time when user set parameters have been chosen in the PEAK SELECT mode.
5.2.9 DISPLAYING TOTAL PRESSURE
5.2.9.1 Total Pressure can be measured in the Peak Select mode, by setting the mass in any channel to "0".
5.2.10 DISPLAYING EITHER TABLE OR CHART
5.2.10.1 The data acquired in the PEAK SELECT mode can be displayed either as a table or a graph. TABLE/GRAPH is a toggle key that alternates between the two displays.
5.2.11 RESETTING EVERYTHING TO PRE-SET (i.e DEFAULT) VALUES
5.2.11.1 Sections 5.2.3 through 5.2.8 describe how the front panel keys are used to control the display on the monitor. When you change these parameters they are stored in the volatile memory of DATAQUAD. The RESET key will put everything back to the factory pre-set values.
5.2.11.2 Do a RESET/POWER-UP as in Section 5.2.3.2 and press PEAK SELECT. Change a number of parameters like GAIN and PRECISION CODE. Press RESET to display a graph with the factory preset values. Press RESET a second time to return to your values and verify that they are still there. Now, return to factory preset with RESET and change the value of just one parameter. When you next press RESET you will find that the factory preset values appear, not the expected user set. That is, whenever you make a change to the factory presets, it wipes out the previous user set because the computer accepts your new change as a complete user set.
5.2.12 USING THE ELECTRON MULTIPLIER
5.2.12.1 The electron multiplier may be used in the PEAK SELECT mode, its operation and the reasons for using it are described in Section 5.1.13.
5.2.12.2 When in the BAR GRAPH mode the multiplier is either on or off for the complete scan. In PEAK SELECT the multiplier can be selected for individual channels.
5.2.12.3 When both Faraday and multiplier detectors are selected in a cycle there is a delay when the switch is made from Faraday to multiplier and vice versa. It is therefore advantageous to group together all channels using the Faraday detector and all those using the multiplier detector. Thus minimising the cycle time.
5.2.13 PRINTING
5.2.13.1 A hard copy printout of the display in the PEAK SELECT mode is obtained in the same manner as described in section 5.1.14.
5.3 AUTOMATICALLY STORING THE EIGHT LARGEST PEAKS
5.3.1 In most vacuum systems it is the largest components that are of most interest. MAX PEAKS is a convenient way to automatically loading information on the eight largest masses into the first 8 channels of PEAK SELECT mode. MAX PEAKS can be selected from any DATAQUAD operating mode.
5.3.2 Press MAX PEAKS (panel 5). The instrument shows the display reading "PLEASE CONFIRM". This a request to remind you that if you have selected MAX PEAKS immediately after POWER UP the next operation will switch on the filament so you must confirm that vacuum is adequate, better than 5 x 10-5 torr.
5.3.3 Confirm that the vacuum is acceptable by pressing MAX PEAKS a second time. The DATAQUAD will follow the sequence given in section 4.4.4 and end in the PEAK SELECT graphical mode displaying the 8 largest peaks in the system.
5.3.4 Selecting MAX PEAKS will erase all previously stored user set masses in the PEAK SELECT mode but it does not prevent you from changing any or all of the masses selected by MAX PEAKS if you wish.
5.4 ANALOGUE DISPLAY
5.4.1 INTERPRETING ANALOGUE DISPLAY
5.4.1.1 In the ANALOGUE DISPLAY mode, the DATAQUAD displays a graph of peak intensity versus mass over a 10 amu span. The display looks like the traditional mass spectrum drawn out on a strip chart recorder and includes peak shape information.
5.4.1.2 It is not a true analogue plot because the display is made up of 20 discrete steps across each amu but it is a sufficiently fine division of the mass scale to look like an analogue output (see Figure 5.4.1).
5.4.1.3 ANALOGUE DISPLAY is used to check the peak shape and resolution of the analyser which are the first indications that the analyser is deteriorating and needs to be cleaned. It is also the display to use when tuning the RF head.
Figure 5.4.1 Analogue Display
5.4.2 ENTERING ANALOGUE DISPLAY
5.4.2.1 Press INDEX (Panel 4) to display a menu of DATAQUAD options on the monitor. Use the arrow keys to highlight ANALOGUE DISPLAY. Press STOP/RUN (Panel 7) to start the scan.
5.4.2.2 Other keys, MASS IDENT, MASS, PREC, GAIN/AUTO, SEM, RESET, PRINT, act in the normal manner in ANALOGUE DISPLAY mode but there is no autogain available.
5.5 MULTICHANNEL TREND ANALYSIS
The TREND ANALYSIS mode may be entered via the INDEX, it operates
on the parameters that have been set up in PEAK SELECT, and can be used to monitor from 1 to 8 channels in TABULAR or GRAPHICAL display formats. The TABLE/GRAPH key is used to toggle between the two alternative displays. Multichannel TREND ANALYSIS data consists of partial pressures referenced to time in minutes and seconds. A hard copy of the data may be generated by using the PRINT key as described below.
5.5.1 ENTERING TREND ANALYSIS
5.5.1.1 Press INDEX to display the menu and use the arrow keys to highlight TREND ANALYSIS. Press the RUN/STOP key.
5.5.1.2 DATAQUAD now prompts you for the time interval to used and displays "00.00" or the last interval selected. Use the arrow keys to select the required interval between 00.00 and 10.00 minutes.
5.5.1.3 Press RUN/STOP to start the TREND ANALYSIS
5.5.1.4 The screen display will change to TREND ANALYSIS giving the time intervals on the left side of the display and partial pressures in each of the channels that have been enabled PEAK SELECT.
5.5.1.5 If more than 8 channels are enabled in PEAK SELECT then the DATAQUAD will run TREND ANALYSIS on the first 8 and disable the rest. If no channels are enabled then DATAQUAD will enable channels 1 to 8 and collect data on these.
5.5.1.6 Depending on the number of channels the run time display will be adjusted to give maximum display reslution to each channel when used in graphical mode.
5.5.2 PARAMETER ADJUSTMENT DURING TREND ANALYSIS
5.5.2.1 PRECISION CODE, DETECTOR, GAIN, MASS and FILAMENTS may all be changed during a TREND ANALYSIS.
5.5.2.2 Note: If a continuous printout is in operation when any of the above parameters are changed, then the change is NOT highlighted on the printout if included in the header information. Change of GAIN or DETECTOR however is printed out whenever either is changed.
5.5.3 PRINT SELECTION DURING TIME INTERVAL SETUP
5.5.3.1 If one of the 3 PRINT options is selected before TREND ANALYSIS starts i.e. at the point when TIME INTERVAL is requested, the following happens:
PRINT Option Effect
_____________________________________________________
"OFF" - No print action on entry to TREND
ANALYSIS run
"SINGLE" - The print mode is set to "OFF" on
entry to TREND ANALYSIS run
"TIMED" - By selecting TIMED at the time when TIME
INTERVAL is requested, then pressing
RUN/STOP, the table header information
is printed before measurement starts,
followed by the data as each time int-
erval elapses.
______________________________________________________
5.5.4 PRINT SELECTION DURING A TREND ANALYSIS RUN
5.5.4.1 If one of the 3 PRINT options is selected during TREND ANALYSIS then the following happens:
PRINT Option Effect
_____________________________________________________
"OFF" - A printout may be terminated at any
time by pressing the PRINT key and
holding it down until the print
status shows "OFF"
"SINGLE" - A full screen dump may be obtained
from the "OFF" state by pressing the
PRINT key once. This will take about
40 seconds and data will be lost during
this time although the time display will
be adjusted to compensate.
"TIMED" - Select TIMED during the run by holding
down the PRINT key and a continuous
printout is commenced but without the
trend table header information. The
gain setting for each channel is given
each time TIMED is selected from OFF
just in case the settings have changed
between printing periods.
5.5.5 PRINT ABORT DURING SINGLE OR TIMED OPERATION
5.5.5.1 A print operation may be aborted at any time by pressing and holding the PRINT key until the OFF status is displayed.
5.5.5.2 If a SINGLE screen dump is aborted then the time reference will be automatically adjusted to number of seconds elapsed during the screen dump.
5.5.5.3 In the graphical mode, a complete line of data will be output to the printer every 8 time intervals whereas in the tabular mode a line of data will be printed every time interval.
5.6 LEAK DETECT
5.6.1 DETECTING LEAKS
5.6.1.1 Leak detection can be done in a variety of ways with a variety of gases, so this is only a brief introduction to leak detection.
5.6.1.2 Leak Checking a Normal Vacuum Chamber.
Before you try to detect the position of a leak, it is a good idea to confirm its existance. One way to do this is to look at the Bar Graph spectrum for the presence of air components, particularly oxygen. Without a peak at 32 there is a strong possibility that no leak exists (unless your system is coated with something that scavenges oxygen).
5.6.1.3 Leak Checking Chambers with Internal Water Connections. Here you should look for an abnormally large 18 peak indicating that a joint is broken and water is evaporating directly into the chamber.
5.6.1.4 Leak Checking Transistors and IC Packs.
This requires special apparatus to puncture the package and look at the gas components released. Contact your Spectramass representative for information on the systems available.
5.6.1.5 Leak Checking Vacuum Components.
The easiest way to leak check a vacuum component is to mount it on a pumping system and close all entrances with gaskets and flanges. Set the DATAQUAD to LEAK DETECT mode. Attach a long flexible hose to a cylinder of helium and spray the gas around all the connections and welds of the vacuum component. If the height of the trend line and the pitch of the audio tone increases, helium has entered the vacuum chamber and been detected by the analyser.
5.6.1.6 If the vacuum component has a poor conductance i.e. made of narrow tube with many bends, this operation should be done rather slowly. There may be a long interval between gas entering the leak and reaching the analyser. Once the helium is detected, wait until the signal is reduced and then respray the area where you suspect the leak. You should be able to pin-point the leak site and take corrective action.
5.6.1.7 Don't forget to spray again after correction to make
sure the leak has been completely eliminated.
5.6.2 DETECTING LEAKS WITH OTHER GASES
5.6.2.1 If helium is not convenient for leak detecting your system you can use argon or one of the freons. Enter the LEAK DETECT mode in the usual way and select the appropriate mass number for the gas you have with the MASS IDENT.
5.6.2.2 The variable pitch sound can be switched off in the LEAK DETECT format by pressing EN/DIS.
5.7 AUTO RUNNING.
5.7.1 AUTO RUN is intended to help the user who does the same analysis day after day and wants to automate the startup.
5.7.2 AUTO RUN should NOT be used if you start your vacuum system fresh every morning because a newly pumping vacuum system will usually have a varying amplitude on the 28 peak because the vacuum is improving and this will cause the DATAQUAD to show a failure code for multiplier calibration at that point in the AUTO RUN start up sequence.
5.7.3 Press AUTO RUN. A message is displayed "PLEASE CONFIRM" that asks if the system pressure is stable and less than 1 x 10-5 torr.
5.7.4 Press AUTO RUN again to start the sequence.
5.7.5 Filament #1 is switched on and the instrument waits about 15 minutes for the filament to out gas and the electronics to stabilise.
5.7.6 The diagnostics program is then run to check the electronics status.
5.7.7 The electron multiplier is turned on and calibrated as described in section 6.9 (dual detector models only).
5.7.8 At the end of the AUTO RUN sequence, the DATAQUAD will begin acquiring data in the BAR GRAPH mode with the user set values.
SECTION 6
________________________________________________________________
"INDEX"
This Section describes the functions available under the INDEX which is best regarded as the menu from which the more sophisticated software options may be selected.
6.1 BAR GRAPH
6.1.1 The normal single screen bar graph mode has been extended to include three additional sub-modes which can be selected via INDEX.
6.1.2 BAR GRAPH mode is an index entry which, when activated by pressing the STOP\RUN key, will cause a Bar Graph mode sub-menu to be displayed which contains four entries:-
SINGLE SCREEN
SPLIT SCREEN
LOG/LOG
LOG/LIN
6.1.3 The required Bar Graph mode may be selected using the arrow keys to move the inverse cursor to one of the four modes in the menu. Pressing either the STOP/RUN key or the BAR GRAPH key at this point will cause the selected mode to be entered.
6.1.4 Note: Each time the BAR GRAPH key is pressed the Bar Graph mode selected will be automatically entered, until the sub-mode is changed again via the INDEX.
6.1.5 Note: A Power-up Reset will reset the Bar Graph to the single screen mode of operation.
6.1.6 SINGLE SCREEN: This mode of operation has been described in detail in Section 5.1.
6.1.7 SPLIT SCREEN: Activation of the Split Screen mode of operation results in the display of two sets of axes. The on-line spectrum will be displayed on the upper axes, whilst the lower axes are used to display the currently selected Mass Spectra (from the library) or one of the user stored backgrounds.
6.1.8 The operation of the upper axes is exactly the same as in the SINGLE SCREEN except that the vertical display has been halved and the PRECISION and GAIN entries now relate to both upper and lower spectra. The upper (on-line) spectrum gain and precision being displayed to the left of the slash. ("/")
Example:- PRECISION ....... 0/-
GAIN ...........F05/- (F-Faraday, M-SEM)
6.1.9 If the lower spectrum is one of the user stored spectra then the PRECISION and GAIN might be displayed as:-
Example:- PRECISION ....... 0/2
GAIN ............ F05/M09A
When in the SPLIT SCREEN mode, the arrow keys may be used to step through the Mass Spectral Library and User Stored Background on the lower axes.
6.1.10 A LIBRARY SEARCH may be activated in the Split Screen mode by moving the Mass Identify Cursor to the mass of interest and then pressing the AUTO RUN key.
When a library search is activated the On-line spectrum is put into the stopped state whilst the search is performed. At the end of the search the number of spectra found containing the selected mass is indicated in the bottom half of the screen together with the first spectrum. At this point, the arrow keys may be used to step through each of the selected spectra. The search process only takes place for the currently chosen file i.e. "Chemical" or "Semiconductor" and not both.
6.1.11 BACKGROUND DISPLAY in Split Screen can be achieved in two ways.
(i) by pressing the BGND DISPLAY key
(ii) by using the arrow keys to step through the
Mass Spectral Library to the end after which
the stored background spectra are automat-
ically displayed.
Note: In each case the background selected will be
displayed on the lower axes.
6.1.12 BACKGROUND STORE in Split Screen is used in exactly the same way as in the normal Bar Graph mode.
Note: The BGND DISPLAY key should always be
pressed to display the current background
prior to doing a BGND STORE so that a wanted
background is not accidentally overwritten.
6.1.13 BACKGROUND SUBTRACT in Split Screen is used in exactly the same way as in the normal Bar Graph mode except that if the background gain and the current on-line gain are not the same, the message "GAIN MISMATCH" is displayed at the top of the screen together with a short warning "beep".
6.1.14 LOG DISPLAY: LOG/LOG versus LOG/LIN.
Both modes of operation perform a Bar Graph scan over three decades of Gain, and display the resultant spectrum.
For the LOG/LOG mode, the peak heights displayed within each decade are logarithmic to base 10, with the y -axis graduations having a scaling of 1-3-5-7-9.
For the LOG/LIN mode the peak heights displayed within each decade are linear with a scaling of 2-4-6-8-10.
6.1.15 AUTORANGING IN LOG DISPLAY. This operation is selected by pressing the GAIN/AUTO key twice and is confirmed by an "A" appearing at the top of the display adjacent to the GAIN display.
6.1.16 Background Display/Store/Subtract are not available in either Log Display mode.
6.1.17 MASS IDENTIFY IN LOG DISPLAY. The partial pressure shown at the top of the display relates to the mass at the MASS IDENT cursor position. The partial pressure reading includes the gain range for the identified mass peak.
6.2. TREND ANALYSIS
6.2.1. The Trend Analysis mode of operation may be entered via the Index. TREND ANALYSIS works on the parameters that have been set up in the Peak Select mode and can be used to monitor channels 1-8 of the sixteen channels available in Peak Select, in either Tabular or Graphical format. The time referenced data (Time in minutes and seconds) can be switched between formats using the TABLE/GRAPH key.
6.2.2. Entering TREND ANALYSIS can be done by highlighting it in the INDEX and pressing STOP/RUN. DATAQUAD then asks for a Time Interval to be entered in minutes and seconds. Use the arrow keys to set a time interval between 00.00 and 10.00 minutes. Press STOP/RUN again to start Trend Analysis.
The display will show TREND ANALYSIS and will be formatted according to the number of channels enabled in Peak Select, up to a maximum of 8. If more than 8 channels are enabled in Peak Select, then the DATAQUAD will only display the first 8 in Trend Analysis. If no channels are enabled in Peak Select then the first 8 are automatically switched on when entering Trend Analysis.
6.2.3. PARAMETER ADJUSTMENT DURING TREND ANALYSIS. PRECISION CODE, DETECTOR, GAIN, MASS and FILAMENTS may all be changed in the normal way.
Note: If a continuous printout is in operation when any of the parameters are changed, the change is NOT shown on on the printout. However, the Gain and Detector are added to the data displayed and hence printed whenever either is changed.
6.2.4. PRINT OPERATION IN TREND ANALYSIS.
OFF - a printout may be terminated at any time by pressing the PRINT key until the print status indicates "OFF".
SINGLE - a full screen dump may be obtained by pressing the PRINT key once. Note that since a full screen dump takes approximately 40 seconds, then this amount of trend data will be lost. The time reference data will be adjusted to compensate.
TIMED - a continuous printout excluding the table header may be enabled by pressing the PRINT key twice. The gain setting for each channel is indicated on the display and the printer in case the gain range setting is changed during the print interval.
Note: In the graphical mode a complete line of data will be output to the printer every 8 time intervals, whereas in the tabular mode a line of data will be printed every time interval.
6.3 DIAGNOSTICS
6.3.1 WHAT DOES DIAGNOSTICS DO?
6.3.1.1 Activating the DIAGNOSTICS routine causes the DATAQUAD to self test seven internal power supplies and check the value of their outputs against stored values in the memory. If any power supply values fall outside the allowed range a "FAIL CODE" is displayed.
6.3.2 ENTERING DIAGNOSTICS
6.3.2.1 Press INDEX and use arrow keys to highlight DIAGNOSTICS.
6.3.2.2 Press STOP/RUN. The DATAQUAD gives out a prolonged 7 second "beep" while the DIAGNOSTIC check is in progress.
6.3.2.3 If all voltages are within tolerance then the message "DATAQUAD OPERATIONAL" will be displayed.
6.3.2.4 If a "FAIL CODE" appears, it indicates that a voltage is outside the allowed limits and must be checked. The FAIL CODES's are explained in section 9.1. Please note the Dataquad should be run for at least 15 minutes prior to running DIAGNOSTICS.
6.4 PROTECT
6.4.1 TOTAL AND PARTIAL PROTECTION
6.4.1.1 DATAQUAD can be protected for overpressure in both total and partial pressures.
6.4.1.2 In TOTAL PRESSURE PROTECT, the filament is tripped if the indicated total pressure exceeds 1 x 10-4torr in either BAR GRAPH mode with the total pressure enabled, or in PEAK SELECT if mass "0" is selected for one of the channels.
6.4.1.3 The PARTIAL PRESSURE PROTECT trips when the partial pressure of any mass exceeds full scale display on the gain range you have set, either in BAR GRAPH or in PEAK SELECT.
6.4.1.4 The effect of the "trip" is to switch off the filament and give a prolonged "BEEP" to indicate a failure. All other supplies remain on.
6.4.2 ENTERING PROTECT
6.4.2.1 Press the INDEX key and use the down arrow to highlight "PROTECT".
6.4.2.2 Press the STOP/RUN key. The display shows "TOTAL" and "PARTIAL" with "TOTAL" highlighted.
6.4.2.3 Toggle between the two protect methods using either arrow key.
6.4.2.4 You can switch either trip "ON" or "OFF" by using the EN/DIS key (Panel 5).
6.5 TIMED PRINTOUT
6.5.1 ENTERING TIMED PRINTOUT
6.5.1.1 The PRINT key cycles through three states; "OFF", "SINGLE", and "TIMED".
6.5.1.2 Press PRINT key until display shows "TIMED". If you have not previously selected a time interval, the DATAQUAD will copy the screen to the printer at the completion of every scan. It will continue to do this until the PRINT key is pressed again and the legend shows "OFF".
6.5.1.3 To enter an interval, select INDEX, use the down arrow until "TIMED PRINTOUT" is highlighted, then press the STOP/RUN key. You will be asked to select a "TIME INTERVAL". Press the up arrow key and the interval changes in minutes. Set in, as an example, "02.0".
6.5.1.4 Now press say, BAR GRAPH and make sure the PRINT legend reads "TIMED". A hard copy of the display will be automatically printed at the end of the next complete scan after 2 minutes has elapsed. Then, after each successive 2 minute intervals, another print will be made at the end of the scan in progress.
6.6 DEGAS
6.6.1 THE PURPOSE OF DEGAS
The ion source of the DATAQUAD has a reasonably open structure so there is little resistance to gas molecules entering the ion source but, as with all ion sources, gas molecules get absorbed onto the metal surfaces.
"DEGAS" is a method of raising the temperature of parts of the ion source to aid outgassing so that there are fewer "desorbable" molecules on the surface.
6.6.2 PROBLEM OF DEGASSING
6.6.2.1 The major problem is to know when to use DEGAS. Many users think that DEGAS is the answer to any contamination that they see, but this is not the case.
6.6.2.2 If the vacuum system is sitting at a steady 1 x 10-6 torr, DEGASSING will cause only a temporary reduction in the adsorbed molecules. The arrival rate of molecules on a surface at that pressure is high so, as the surface cools, back go the molecules. If your vacuum reaches 1 x 10-8 torr or better, then DEGAS is of benefit.
6.6.2.3 If you see considerable evidence of hydrocarbons, peaks at 39, 41, 43, 55, 57, etc, please do not think that DEGAS will remove them. If the vacuum chamber pressure is low enough to warrant it, try a DEGAS, but if the hydrocarbon or other contaminant peaks return after DEGAS then the problem is in the chamber and not in the ion source.
6.6.2.4 Another factor to consider with DEGAS is the strain that it puts on the analyser filament. During DEGAS the filament is in an environment in which the temperature of the surrounding structure has increased by maybe 400 degrees C. This tends to increase the already high temperature of the filament and can cause premature burn-out.
6.6.3 ENTERING DEGAS
6.6.3.1 Press INDEX and use the arrow keys to highlight the DEGAS.
6.6.3.2 Press STOP/RUN. Two digital clocks appear, one recording elapsed time and the other time remaining. DEGAS operates for a total of four minutes and at the end of this period the display reverts to the INDEX list.
6.6.3.3 If you wish to cancel the DEGAS at any time during this four minutes, simply select another function.
6.6.3.4 If you wish to shorten the length of time for which DEGAS operates, press the down arrow. The clock indicating time remaining will step to a smaller number of minutes.
6.7 ALARM OUTPUT/ ANALOGUE OUTPUT
6.7.1 USING ALARM OUTPUT
The INDEX shows the legend "ALARM OUTPUT" when first started from RESET/POWER UP condition. This indicates that in PEAK SELECT the ALARM arrows are enabled and alarm signals are available at the ALARM OUTPUT connector on the DATAQUAD rear panel. See Section 4.5.4
6.7.2 CHANGING FROM ALARM OUTPUT TO ANALOGUE OUTPUT
6.7.2.1 The internal program of the DATAQUAD includes the software required for operation of an ANALOGUE OUTPUT module. This is fully described in section 12 under the heading "PROCESS CONTROL INTERFACE". In order to prepare the DATAQUAD for use with this module it is necessary to change from "ALARM OUTPUT" to "ANALOGUE OUTPUT".
6.7.2.2 To change the output mode, press INDEX, highlight "ALARM OUTPUT" and press STOP/RUN. The legend will change to "ANALOGUE OUTPUT".
6.7.2.3 When ANALOGUE OUTPUT is selected the alarm key does not function in Peak Select mode and no arrows appear.
6.8 TOTAL PRESSURE ENABLED/DISABLED
6.8.1 TOTAL DISABLED
6.8.1.1 The DATAQUAD is able to make Total Pressure measurements by changing the filtering effects of the analyser. In the default condition the Total Pressure measurement is disabled.
6.8.2 MAKING TOTAL PRESSURE MEASUREMENTS - BAR GRAPH
6.8.2.1 To make Total Pressure measurements in BAR GRAPH, press INDEX, highlight TOTAL DISABLED, and press STOP/RUN. The legend will change from "TOTAL DISABLED" to "TOTAL ENABLED".
6.8.2.2 Press BAR GRAPH and note that the display has changed so that the Total Pressure can now be seen in the upper right hand corner of the screen. The value will be updated at the end of the every scan.
6.8.2.3 When Total Pressure measurement is not needed, it is preferrable to switch the DATAQUAD to TOTAL DISABLED so as to avoid the interscan delays.
6.8.3 MAKING TOTAL PRESSURE MEASUREMENTS - PEAK SELECT
6.8.3.1 To make Total Pressure measurements in PEAK SELECT, press PEAK SELECT and move the highlight to the channel number of your choice. Then press MASS and use the down arrow to select "MASS 0"
6.8.3.2 The "partial pressure" indication for MASS 0 is then the Total Pressure.
6.8.3.3 When Total Pressure measurement is not needed, it is preferrable for the DATAQUAD to read normal masses rather than mass 0.
6.8.4 NOTES ON TOTAL PRESSURE MEASUREMENT
6.8.4.1 The total pressure measurement for DATAQUAD is meant to be a good indication of the true Total Pressure however, total pressure as measured by the DATAQUAD may differ somewhat from that indicated by an ion gauge that may be mounted in the same system. Before leaving the factory the DATAQUAD's total pressure measurement is set against a calibrated ion gauge.
6.8.4.2 It is not unusual, in other operating conditions, for the DATAQUAD and an ion gauge to give different indications. This is particularly true if the system has cryo or ion pumps, or if the ion gauge and the analyser are not in exactly the same vacuum environment.
6.8.4.3 Further, the method used by DATAQUAD to measure the Total Pressure will not include any gas components at masses below 10 amu so, if the gas mixture to be measured contains appreciable amounts of hydrogen or any other low mass gas, there will be a large difference between the DATAQUAD's Total Pressure and an ion gauge.
6.9 MULTIPLIER CALIBRATION
6.9.1 WHAT DOES MULTIPLIER CALIBRATION DO?
6.9.1.1 The Secondary Electron Multiplier (SEM) fitted to DATAQUAD DXM Models only, amplifies the ion current signal. If a gas in the vacuum system produces say 1000 positive ions per second at a particular mass as measured at the detector, then the SEM will convert this into a current equivalent to 100,000 electrons per second.
6.9.1.2 If the multiplication factor is not 100, then the SEM requires calibration. The purpose of the MULTIPLIER CALIBRATION routine is to calculate the actual multiplication factor and if necessary reset it to 100. This is achieved by adjusting the voltage across the SEM.
6.9.2 HOW DOES MULTIPLIER CALIBRATION WORK?
6.9.2.1 The DATAQUAD sets the mass to 28 and measures the amplitude of that peak using the Faraday Detector. If the pressure of this peak exceeds a factory set partial pressure value, DATAQUAD automatically switches to mass 12 and attempts to calibrate there. If that partial pressure is also too large, there is a good chance that the pressure is so high in the system that you should not be attempting to use the SEM.
6.9.2.2 Having selected the calibration peak, DATAQUAD adjusts the GAIN until the peak is on scale and then measures the ion current with the Faraday Detector.
6.9.2.3 DATAQUAD waits 5 seconds and then re-measures the ion current. If these two measurements agree within 5%, DATAQUAD accepts that it has a stable peak to measure and switches on the multiplier voltage.
6.9.2.4 Now DATAQUAD switches down the GAIN by 100 and measures the electron current from the multiplier. (Actually, it switches in an attenuator of 100 while leaving the GAIN indication as it was for the Faraday measurement). If the electron current (after attenuation) equals the ion current from the Faraday detector, in magnitude but not sign, then the multiplier is calibrated. If the electron current does not equal the ion current, then the program automatically changes the voltage applied to the multiplier to adjust its gain factor.
6.9.2.5 When the two currents are equal in magnitude, the display reverts to the INDEX list.
6.9.2.6 If for some reason the two currents cannot be made equal or the signal shows some instabilities at some stage of the measurement then a Fail Code is displayed. For an explanation of Fail Codes see section 9.2
6.9.3 ENTERING MULTIPLIER CALIBRATION
6.9.3.1 Press INDEX and use the arrow keys to highlight "MULTIPLIER CALIBRATE". Press STOP/RUN and the display shows "PLEASE CONFIRM". This is to remind you to check that the pressure is below 1 x 10-5torr. If this is so then press STOP/RUN again and the display now shows the flashing sign "OPERATING".
6.9.3.2 If you watch closely you can sometimes see the GAIN change as the DATAQUAD finds the correct factor to keep the peak on scale. If the various tests of stability are passed, the multiplier is switched "ON" and the calibration process takes approximately 20 seconds.
6.9.3.3 If calibration is successful, the display automatically reverts to the INDEX list.
6.10 MASS SPECTRA
6.10.1 A REFERENCE LIBRARY OF MASS SPECTRA
6.10.1.1 The mass spectrum of a pure compound, shows characteristic mass peaks with particular relative amplitudes. It is useful to have copies of spectra of known gases and vapours to match with the spectra of the unknowns in your gas sample. This comparison allows you to make a judgement on the presence or absence of specific components.
6.10.1.2 The DATAQUAD has a library of stored spectra to help with spectral interpretation.
6.10.2 ENTERING THE LIBRARY
6.10.2.1 Enter the INDEX and use the down arrow to highlight the legend "MASS SPECTRA". Press the STOP/RUN key and the screen will show a list of 16 components that are stored in the library.
6.10.2.2 Use the down arrow to step down the list. If you attempt to go beyond the last component listed the page changes to the next 16 components. To return to the former page, use the up arrow to go beyond the top entry on the list.
6.10.2.3 Select the component you wish to see by highlighting the name and pressing the STOP/RUN key. The display will show the bargraph spectrum of that component which can then be printed in the normal way.
6.10.3 COMPARING YOUR RESULTS WITH THE LIBRARY
6.10.3.1 This is no more than the briefest introduction to mass spectral matching.
6.10.3.2 Spectral Library comparisons can often give an affirmative answer to the question "is this component absent from the vacuum ?" but cannot always give an assurance that the component is present. As with fingerprint matching, the more similarities that exist, the stronger the possibility of a match.
6.10.3.3 Note the mass number of the largest peak in the library spectrum. Look at the same mass in the mass spectrum from the system. Is the peak present in the unknown? If yes, note the second largest peak in the library and again look for a corresponding peak in the system spectrum. If it is present, is it large enough to give roughly the same peak height ratio of second/first as the library spectrum?
6.10.3.4 Continue the comparison process for all five peaks in the library spectra, always noting if the unknown could give a similar peak ratio. It is important to remember that the reference spectrum is of a pure substance but that actual spectra are always a mixture of various components. This means that a particular peak in the sample spectrum could be made up of contributions from several gas components thus distorting the ratios.
6.10.4 SELECTING THE LIBRARY
6.10.4.1 Two mass spectral libraries are included in DATAQUAD, a CHEMICAL library and a SEMICONDUCTOR library.
6.10.4.2 To select the appropriate library file enter the INDEX and highlight MASS SPECTRA. The currently selected file will be highlighted. Use the arrow keys to select the other file if necessary then press STOP/RUN. The following library spectra are available:
CHEMICAL LIBRARY SEMICONDUCTOR LIBRARY
-----------------------------------------------------
1 Methane Air
2 Ammonia Argon
3 Water Arsine
4 Neon Boron Trichloride
5 Acetylene Boron Trifluoride
6 Ethylene Bromo Trifluoromethane
7 Carbon Monoxide Carbon Dioxide
8 Nitrogen Carbon Monoxide
9 Ethane Carbon Tetrachloride
10 Nitric Acid Chloroform
11 Methanol Diborane
12 Oxygen Diphoshine
13 Hydrogen Disulphide Disilane
14 Argon Fomblin OIl
15 Propene Freon-12
16 Propane Hydrogen Chloride
17 Carbon Monoxide Ispropyl Alcohol
18 Nitrous Oxide Methane
19 Acetaldehyde Nitrogen Trifluoride
20 Ethanol Phosphine
21 Nitrogen Dioxide Rotary Pump Oil
MASS SPECTRA LIBRARY (Continued)..............
22 Formic Acid Silane
23 Butane Silicone Diff. Oil
24 Acetone Silicon Tetrafluoride
25 Isopropyl Alcohol Tetrafluoromethane
26 Acetic Acid Trichloroethylene
27 Ethylene Glycol Triethylphosphine
28 Vinyl Chloride Trifluoromethane
29 Sulphur Dioxide Trimethylaluminium
30 Carbon Disulphide Trimethylgallium
31 Benzene Trimethylindium
32 Toluene Water
----------------------------------------------------
6.11. ANALOGUE DISPLAY
6.11.1 INTERPRETING ANALOGUE DISPLAY
6.11.1.1 In the ANALOGUE DISPLAY mode, the DATAQUAD displays a graph of peak intensity versus mass that looks like the traditional mass spectrum drawn out on a strip chart recorder. See Figure 6.11.1.1.
Figure 6.11.1.1 Analogue Display
6.11.1.2 It is not a true analogue plot but made up of 20 steps across each amu (Atomic Mass Unit). This is a sufficiently fine division of the mass scale to enable the peak "shape" to be displayed as it would be seen in the traditional analogue recorded output.
6.11.1.3 ANALOGUE DISPLAY is used to check the peak shape and resolution of the analyser over a 10 amu range (see Section 5.4.1). Changes in these characteristics are the first indications that the performance of the analyser is deteriorating due to contamination and needs to be cleaned.
6.11.1.4 As it is used mostly as a diagnostics tool, the mass "window" of 10 amu is not adjustable but the window can be moved anywhere in the mass scale.
6.11.2 ENTERING ANALOGUE DISPLAY
6.11.2.1 Press INDEX (Panel 4). One of the last items on the list is ANALOGUE DISPLAY. Use the Up/Down Arrows to highlight it, then press STOP/RUN (Panel 7) to start the scan.
6.11.2.2 The ANALOGUE DISPLAY graph is shown with either the factory preset value of the mass scale or the last user set value. DATAQUAD automatically scans that mass scale.
6.11.2.3 The scan parameter keys, MASS, PREC, SEM, RESET and PRINT, interact in their normal manner in ANALOGUE DISPLAY. The Up/Down keys then change that value as normal.
6.11.2.4 GAIN/AUTO will operate to select GAIN as the highlighted function but Automatic Gain mode is not available in Analogue Display.
6.12. RS 232/ IEEE ACTIVE
6.12.1 The RS232 Interface is standard in all current DATAQUADS. The IEEE interface is an additional plug in unit.
6.12.1.1 Whenever a computer interface is plugged into the "EXPANSION BUS", the DATAQUAD detects its presence and displays this recognition by adding the appropriate legend to the INDEX , i.e. "RS232 ACTIVE" or "IEEE ACTIVE".
6.12.1.2 For the IEEE, the recognition indicates that the interface is plugged in correctly. The RS 232 interface recognition indicates not only correct connection but also allows the baud rate of information transfer to be changed. (See below)
6.12.2 CHANGING THE BAUD RATE OF THE RS 232
6.12.2.1 The baud rate of information transfer can be adjusted to any of the following rates 50, 150, 300, 1200, 2400, 4800, 9600, 19200.
6.12.2.2 To check the baud rate, press INDEX, use the Down Arrow to highlight the legend RS 232. Press the STOP/RUN key and the display changes to show the default condition of "BAUD RATE 1200".
6.12.2.3 To change the baud rate press the Up/Down Arrows to select the rate required.
SECTION 7
________________________________________________________________
ANALYSER MAINTENANCE.
7.1 INTRODUCTION
7.1.1 GENERAL
There is little that can be done to a quadrupole analyser as
regards preventative maintenance but that does not mean that a quadrupole never needs maintenance to restore performance after normal wear and tear. Recognising when this maintenance is needed and how to carry it out is explained in this section.
7.1.2 WHAT NEEDS TO BE MAINTAINED
There are two components of the mass analyser which are slowly degrading during normal use, the ion source and the mass filter.
7.1.2.1 The ION SOURCE uses a filament that is held at white heat so as to eject electrons and effect ionisation. This causes a number of deleterious things to occur. The metal of the filament evaporates and the filament gets thinner and eventually goes open circuit (O/C). The metal vapour deposits itself on analyser components of which the insulators are the most sensitive. Sometimes chemical reactions occur between the sample and the filament wire producing more rapid errosion. Perhaps the most common filament failure is caused by a rapid increase in pressure in the chamber creating high filament temperatures and consequent burn out. Changing filaments and cleaning the ion source are two maintenance jobs described here.
7.1.2.2 During the course of its job the MASS FILTER selects ions according to their mass to charge ratio. The selected ions pass through the centre of the quadrupole rods to arrive at the detector and become part of the ion current being measured. The ions not selected have unstable oscillating trajectories and strike the metal surfaces of the analyser. It is the filtered ions that strike the rods themselves that cause a problem as they gradually build up a layer on the quadrupole rods which adversely affects the performance. This happens to all analysers and cannot be avoided. Cleaning the quadrupole rods is another maintenance job described here.
7.2 CHANGING FILAMENTS
7.2.1 DETECTING FILAMENT BURN OUT
7.2.1.1 The first indication of filament burn out is that the spectrum disappears. The display also gives a flashing "O/C" signal for the particular filament. To confirm that the filament has blown, remove the RF box from the mass filter and measure the resistance between pin 7 and either pin 4 (Fil #1) or pin 8 (Fil #2). The pins are counted clockwise from the gap. The measured resistance should be 0.3 ohms or less. If you measure a large resistance or open circuit then change the filament as described in section 7.2.2.
Note: DO NOT SWITCH ON THE OTHER FILAMENT WITHOUT FIRST CHECKING THE SYSTEM PRESSURE - THIS MAY BE THE CAUSE OF THE FAILURE AND YOU WILL HAVE TWO FILAMENTS TO CHANGE INSTEAD OF ONE
7.2.2 PREPARING TO CHANGE A FILAMENT
7.2.2.1 Follow the correct shut down procedure for your vacuum system and let it up to atmospheric pressure. Un-bolt the analyser from the vacuum chamber and re-check the resistance across the filament posts to confirm that the filament has broken. The filament assemblies can be identified as the crescent moon shaped pieces on the top plate of the analyser. Filament 1 has just one barrel connector attached to the feedthrough lead and Filament 2 has two. This is because the filaments share a common return wire.
7.2.2.2 It is important to ensure that the analyser is in a stable condition before starting to work on it. This can be achieved by placing the feedthrough end of the analyser into the aluminium container in which it was delivered and then gripping the flange edge of the analyser in a horizontal jawed vice so that the axis of the mass filter is vertical.
7.2.3 TOOLS AND MATERIALS NEEDED
7.2.3.1 Equip yourself with the following items:
needle nose pliers,
small tweezers,
small jewellers screw-driver,
lint free paper,
new filament,
gloves,
7.2.3.2 Note: The wearing of suitable gloves is very important. They should be either cotton gloves or the non greasy plastic ones provided in the DATAQUAD spares/tool kit.
7.2.3.3 Remember that we are trying to protect the analyser from any material that gets onto it including finger prints, which will slowly burn off resulting in a very strange spectrum.
7.2.4 MECHANICS OF CHANGING A FILAMENT
Figure 7.2.4 Changing a Filament
7.2.4.1 Hold the barrel connector with the needle nose pliers along the length of the connector. Loosen the screw in the barrel connector that is parallel to the axis of the analyser. Remove the long wire from the barrel connector. Undo the two screws that hold down the crescent shaped filament assembly and put them onto a piece of lint free paper with