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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

2.3 INSPECTING AND MOUNTING THE ANALYSER

2.4 ELECTRICAL CONNECTIONS

3. INITIAL OPERATIONAL CHECK-OUT

3.1 VACUUM REQUIREMENTS

3.2 CHECKOUT PROCEDURE

4. CONTROL Buttons AND THEIR FUNCTIONS

4.0 INTRODUCTION TO OPERATION

4.1 BACK-UP COPIES OF SOFTWARE

4.2 LOADING THE SYSTEM

4.3 USING THE MENU SYSTEM

4.4 SETTINGS MENU

4.5 THE LOAD AND SAVE SETTINGS SUB OPTIONS

4.6 BAR GRAPH MODE

4.7 ANALOG MODE

4.8 CHANNEL AND TREND MODES

4.9 LEAK DETECT MODE

4.10 ANALYSE MODE

4.11 OTHER FEATURES AND OPTIONS.

5. RS232 COMMANDS (Option)

6. LOGGED DATA FORMAT

7. ANALYSER MAINTENANCE

7.1 INTRODUCTION

7.2 CHANGING FILAMENTS

7.3 CLEANING THE ION SOURCE

7.4 CLEANING THE MASS FILTER RODS

8. TROUBLESHOOTING

8.1 POWER

8.2 DISPLAY

8.3 TOTAL PRESSURE

8.4 SPECTRUM

8.5 FILAMENTS

8.6 MULTIPLIER

8.7 PRINTER

8.8 VOLTAGE CHECKS AND REPAIRS

This manual is divided into sections that introduce you progressively to the many features of the DQC. 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 DQC.

In outline, the Sections contain:

Unpacking, inspection and installation instructions.

Quick directions for operating the DQC2000 in order to achieve a spectrum. This is not an alternative to reading the manual but a confidence builder to prove you are not reading in vain.

A comprehensive description of the operation of DQC2000 and all its modes of operation. It is a useful reference section until you have sufficient operating experience to ignore it.

Detailed operating instructions for computer communication with DQC2000 using the standard RS 232.

Descriptions of the logged data format for transporting data into other software packages such as spread sheets.

This section introduces the little but necessary routine maintenance that must be done on a quadrupole.

A troubleshooting guide.

2.1 UNPACKING AND CHECKING VISUAL DAMAGE

2.1.1 When you receive the DQC2000, carefully check each item by removing the packing material to ensure that no physical damage has occurred during shipment. Also make sure that all items have been received by checking against the packing note.

2.1.2 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 representative, or LARIMAX.

2.1.3 Most insurance claims for shipment damage must be sub-mitted in WRITING within 7 days from the date of delivery so please inspect your DQC2000 as soon as you receive it.

2.2 BEFORE YOU INSTALL THE MASS FILTER

2.2.1 The analyser is normally supplied in a UHV compatible housing terminating in a CF35flange. The vacuum chamber onto which you intend to mount the analyser must have a corresponding flange.

2.2.1.2 If your chamber has the wrong flange, then you will need to use an adaptor. Please contact your LARIMAX 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.

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 DQC2000 during sputtering or etching will not prevent this contamination and, worst of all:

2.2.2.3 We do, however, supply High Pressure Adapter Kits for just these types of applications so please contact us for assistance.

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 PACKING.

2.3.1.1 The analyser is shipped in protective packaging. This should be carefully opened and the analyser removed. Hold the analyser by the housing and do not touch the part which goes into the vacuum system.

2.3.2 MOUNTING THE ANALYSER TO THE VACUUM CHAMBER

2.3.2.1 The standard 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, place it on the end of the housing and set it in the grooves of the flange surface.

2.3.2.3 Carefully offer the analyser upto the vacuum chamber flange rotate the analyser so the location spigot is positioned to the right, and fit the nuts, bolts and washers. Make sure the gasket does not slip part-way out of its slot as you push the two flanges together. An extra pair of hands may be useful to complete this operation.

2.3.2.4 The preferred orientation of the analyser is horizontal.

2.4 ELECTRICAL CONNECTIONS.

GENERATOR

1. The RF Generator and pre-amplifier is contained within a small box that plugs directly onto the back of the analyser. 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. 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.
0. The 25-way jacketed cable from the RF generator connects to the 25-way D-socket on the supplies unit labelled "Analyser Head". Connect the 2m co-axial cable labelled "SEM" (If fitted) emerging from the RF generator to the socket labelled "SEM" on the rear of the supplies unit.
1. Make sure that the POWER switch on the supplies unit is in the OFF (out) position. Connect the mains power lead BUT do not switch on the power at this stage.

2.4.2 ELECTRICAL CONNECTIONS TO THE COMPUTER

2.4.2.1 The DQC2000 quadrupole requires an IBM compatible PC for operation. This may be supplied by LARIMAX or you may use a suitable unit of your own. In either case the computer must be dedicated to the DQC2000 whilst operation of the quadrupole is required. If the computer is supplied by LARIMAX, then read section 2.4.2.2. If you are supplying your own computer then continue reading from section 2.4.2.4.

2.4.2.2 The DQC2000 requires an interface card. When the computer system is purchased from LARIMAX, this card will already be fitted in a convenient slot within the computer. Connect the computer, monitor, keyboard and mouse according to the manufacturers manual supplied with the computer. Using the cable supplied, connect from the 25-way D-connector at the rear of the computer to the 25-way D-connector on the supplies unit labelled "Interface".

2.4.2.3 The software is pre-installed on the hard disk and is stored in the directory C:\DQC2000. A back up copy of the software is supplied on floppy disk and this should be stored safely in case of future need. Please continue reading from Section 2.4.3.6.

2.4.3.4 When the computer system is not supplied by LARIMAX, the interface card needs to be fitted into the computer to be used. The minimum requirements are 486 compatible with SVGA display and a free expansion slot. Switch off the computer and remove the cover according to the manufacturers instructions. Fit the interface card into a spare ISA slot. Fit the 25-way D-connector plate to a suitable aperture on the rear panel of the computer. Use the cable supplied to connect from this D-connector to the 25-way D-connector on the supplies unit labelled "Interface".

2.4.3.5 The software is supplied on floppy disk (Or CD). This should be copied onto your hard disc.

Follow instructions supplied with the disc.

The floppy (CD) disks supplied should now be safely stored as back ups in case of future need.

The procedure given in this section is designed to check that the

DQC2000 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. It assumes that the software has been installed to the hard disk.

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 DQC2000 at significantly higher pressure will lead to unreliable performance and/or damage to the analyser filaments and multiplier.

DETECTOR PRESSURE LESS THAN

FARADAY 1 x 10-4Torr

MULTIPLIER 1 x 10-6Torr

3.2 CHECK-OUT PROCEDURE

3.2.1 SWITCH ON PROCEDURE

3.2.1.1 THE SWITCH ON PROCEDURE IS CRITICAL. ALWAYS USE THE FOLLOWING PROCEDURE.

3.2.1.2 Switch on the Computer and allow the software to load. When the message appears-"Check pressure is below 10e-4 etc" then switch on the DQC2000 supplies unit. DO NOT switch on the DQC2000 unit UNTIL the computer is on and the DQC2000 software is loaded.

3.2.2 OBTAINING A SPECTRUM

3.2.2.1 Wait until you see the "CHECK PRESSURE IS BELOW 10-4" message and then click 'Standard Software'. The opening panel will disappear. Now switch on the emission by selecting 'FIL1' button. A message should appear in the message box below the x-axis which informs you that Filament 1 is on. Now select Start in the scan panel.

The message box will change to 'Instrument on line'.

A spectrum (represented by a series of bars) should start to appear on the screen as the instrument scans. It may be necessary to increment the gain before it appears depending on the quality of your vacuum and size of the peaks. If you see bars at typically masses 17, 18, 28 and 44 then all is well.

The QUADRUPOLE is equipped with a comprehensive software package for control of the mass spectrometer and for subsequent data analysis. The software provides six modes of operation and the results are displayed graphically.

The software is easy to operate. It is mouse controlled by clicking buttons in the display area, or buttons on the various toolbars. This allows the user to quickly become familiar selecting the desired options.

The software is supplied on a single 3.5" floppy disk. It is recommended that at least one backup copy is made. It is recommended that a backup copy should be write protected. It should be kept in a safe place separate from the floppy disk supplied with the DQC2000. If you need to obtain further copies of the software from LARIMAX then please contact your local agent.

Switch on the DQC2000 supplies unit. To load the software simply switch on the computer. Do not switch on the control unit before the computer (see 3.2.1.1 above). After a short a display panel will appear with the title "LARIMAX INSTRUMENTS" along with a Check pressure message, and two selection buttons 'Standard Software' or 'Autorun'.

CHECK PRESSURE IS BELOW

1*10E-4 torr

THEN SELECT 'Standard Software' .

Having ascertained that it is safe to do so select 'FIL1'.

Along the top of the screen there are 6 pop down menus with the following headings.

1. File.

2. Display Mode.

3. System.

4. Options.

5. Scan Mode.

6. Help.

In this section the use of the menu system is explained.

Clicking the mouse pointer on any option will produce a pop down menue. If we select File we will see the following 6 options.

File sub menue

1. Save Settings

2. Load Settings

3. Save Spectra

4. Retrieve Spectra

5. Print

6. Exit

The default settings of all the parameters for the instrument's operation are saved to disk and recalled on power-up. Subsequent changes via the menu system can be made without altering the file containing the default values. At any time the spectrometer can be reset to operating according to the default settings by selecting the LOAD SETTINGS option.

If it is desired to save a new set of default settings so that the power-up state of the instrument is the one currently pertaining, then the SAVE SETTINGS is the option to use. To do this click on the 'Save Settings' on the pop down menue. The current parameters are now saved to disk, overwriting the previous values so that all subsequent power ups and LOAD SETTINGS commands place the mass spectrometer in a state identical to that when this SAVE SETTINGS command was last issued. To load the default settings at any time depress the 'Load Settings' button on the top toolbar.

4.5.1 Save Spectra

Clicking the mouse pointer on this option will save the current spectra being displayed into a text file. A dialog box will appear prompting you to enter a filename with an extension the appropriate extension will already be present depending on which operating mode is being used.

The following extensions are used to enable the retrieve spectra facility to list the appropriate stored spectra (see below) :-

In Bargraph mode .bar

In Analogue mode .alg

In Channel mode .chn

Any previously stored spectra can be displayed. Clicking the mouse pointer on this option will produce a dialog box with a list of previously stored spectra. To view the spectra select the file of interest and then select 'open'. Only stored spectra pertaining to the current operating mode will be displayed.

e.g. If you are in Bargraph mode then only spectra which have previously been stored with a .bar extension will be displayed.

If you wish to display a spectra which was previously stored from channel mode, then it will be necessary to select channel mode first and then select 'retrieve spectra'. The dialog box will now contain a list of previously stored channel spectra which will contain the .chn extension.

The PRINT MODE option selects the frequency of sending an output to a printer. There are three methods available, which are SINGLE, TIMED, and PER SCAN. They each have particular advantages that will now be described. The SINGLE printout provides a hard copy of the current scan and is used to get one-off prints of interesting results. The TIMED printout produces an output after a period set by the PRINT INTERVAL. This can be useful for long, slow moving processes where the exact time of a change is not important. The third option, PER SCAN, follows the results of each scan. This may be best used to monitor relatively rapid changes over a short period of time. The PRINT INTERVAL allows the period between TIMED printed outputs to be adjusted between 1 and 60 minutes.

This selection is made when you wish to close the quadrupole down, and exit the programme. Follow the on screen instructions and switch off the control unit when prompted to do so.

Display Mode sub-menue

1. Bargraph

2. Analogue

3. Channel

4. Trend

5. Leak Detect

6. Analyse

In BARGRAPH mode a region of the mass spectrum is measured at integral values of mass number and the resulting partial pressures plotted against mass number in a bargraph format. The PARAMETER options associated with this measurement mode are FIRST MASS SCAN, WIDTH, PRECISION, GAIN and, if a multiplier system has been specified, DETECTOR.

Filament 1 may be switched on by pressing the "FIL1" Button. Similarly, pressing "FIL2" button selects Filament 2, and automatically switches Filament 1 off, if selected. To switch either filament off then depress the 'OFF' button.

The FIRST MASS option is used to set the start of the measurement cycle. Adjusting the scroll bar in the following way may change the value.

Clicking the end buttons will increment or decrement the mass by 1amu. Clicking the space either side of the cursor will increment or decrement the mass by 10amu. To change the mass over a wide range quickly, then select and drag the adjustable cursor by keeping the mouse button depressed. As the first mass changes so does the last mass displayed to keep the display span constant. The first mass scroll bar and scan width scroll bar are interlocked, so the maximum first mass depends on the scan width setting.

After changing the first mass, it is necessary to wait for a complete scan cycle before the new masses will be correctly displayed.

NOTE: If the scan width is set to maximum then the first mass cannot be increased.

The SCAN WIDTH is set by adjustment of the scan width scroll bar in much the same way as for the FIRST MASS.

Adjusting the scroll bar in the following way may change the value.

Clicking the end buttons will increment or decrement the mass by 1amu. Clicking the space either side of the cursor will increment or decrement the mass by 10amu. To change the mass over a wide range quickly, then select and drag the adjustable cursor by keeping the mouse button depressed.

The maximum scan width that can be set is the maximum mass range of the instrument. The last mass scanned will be the sum of the FIRST MASS and the SCAN WIDTH, assuming that this is less than the maximum mass of the instrument, otherwise it sets to the maximum mass that the instrument can measure. As a new value is selected for the SCAN WIDTH the scan width will blank and the axes will be redrawn to suit the new value.

Note: The Scan Width scroll bar is interlocked with the first mass scroll bar, so it may be necessary to reduce the first mass setting to achieve the desired scan width setting.

Starts or continues the scan.

If the scan has been stopped during a scan then clicking the start button will start the scan from the stopped position.

If reset was selected prior to selecting 'start' then the scan will start from the first mass setting, or channel 1 if in channel mode.

Stops the instrument scanning in its current position.

Resets the scan position to either first mass or channel 1 depending on mode.

The PRECISION code sets the amount of time spent measuring each peak in the mass spectrum. The higher the precision code number the longer the time spent on the measurement and hence the better the noise rejection. This is achieved in practice by increasing the number of averaged readings taken on each peak and also increasing the settling delays allowed for the system to attain stability.

The PRECISION codes are variable between 0 and 12. 0 is intended for a rapid scan of the species in the vacuum system and should only be used where a quick look at the quality of vacuum is needed with minimal accuracy. For proper application work the following guidelines may be used for selecting a suitable precision code for the actual conditions being used.

Gain setting Collector Precision

10-5 to 10-7 Faraday 1 to 5

10-8 or 10-9 Faraday 3 to 7

10-10 or 10-11 Faraday 5 to 8

10-7 to 10-9 Multiplier 1 to 5

10-10 or 10-11 Multiplier 3 to 7

10-12 or 10-13 Multiplier 5 to 8

Precision codes greater than 8 can be selected at any time when the best possible detection is required. However scanning speeds are greatly reduced.

The GAIN option allows the user to select the gain range of the amplifier on which measurements are performed. A particular gain range is conventionally identified by the number of amps produced by the detector to give an output of 1V from the amplifier (remember that its full scale output is 10V). The Faraday detector has gain ranges from 10-5 to 10-11 mBar while a multiplier (if fitted) will have the gain ranges 10-7 to 10-13 mBar.

To select Auto Gain in either Bargraph or Analogue Mode depress the button marked 'AUTO on the gain display panel. When selected the software will check the largest peak in the spectrum at the completion of a scan, The gain will be increased to the maximum permitted without the largest peak exceeding Full Scale.

The SEM and CAL buttons will only be enabled for an instrument equipped with dual Faraday and multiplier detectors. There are 3 options allowing the user to select the Faraday cup detector, select the SEM (Secondary electron multiplier detector) and CAL (to calibrate the SEM).

The FARADAY detector is a standard low sensitivity, high pressure ion detector. It can be used for the detection of substantial peaks within the spectrum. The Faraday detector is the default detector.

The secondary electron multiplier, or SEM is a high sensitivity, low pressure ion detector. It is prone to damage by too large an incident ion beam or by operation in too high a pressure, so prior to selecting the SEM ensure that the pressure in the vacuum chamber is less than 10-5mbar. The advantage of using the SEM is the large increase in sensitivity compared with a Faraday detection system. Thus it is used for measuring small peaks which are too low in intensity for the Faraday detector to be used.

The SEM is a current amplifier, the gain of which is set by an applied voltage. Clearly for the device to be of use in a quantitative mode the gain must be accurately known. When this option is selected measurements of the same peak are taken on both Faraday and SEM and the gain of the latter is adjusted so that its output is 102, 103, 104 or 105 times that of the former according to the selection made under the SEM GAIN option. The first peak chosen for this operation is mass 28. This is measured on the Faraday detector first and the current checked to be below 10-8mBar. If this is the case then the calibration may be carried out as described. In the event of the mass 28 peak being too big then mass 29 is investigated for suitability in the same way. If this too is deemed too large for the calibration then the next mass is selected until a suitable peak is found. If no peak is found by the time the instrument reaches 50amu then the calibration is aborted. During this process a number of messages are displayed in the middle of the screen in order to keep the operator informed as to the progress of the calibration.

The TOTAL option when selected causes a measurement of TOTAL PRESSURE to be taken at the end of each scan. The value for TOTAL PRESSURE is displayed at the top right of the screen. Total pressure is always measured using the FARADAY detector irrespective of the DETECTOR setting.

This mode is very similar to the BARGRAPH mode, except that the whole of the scan window is measured and reported so that the actual peak shapes may be scanned.

This mode is mainly used to check on the analyser performance and to check peak shape, resolution and peak position on the mass scale.

The display options and control buttons are the same and described under bargraph mode.

The CHANNEL and TREND modes are identical operationally but differ in the way that the recorded data is presented. In both cases the mass spectrometer makes measurements of partial pressure at up to sixteen mass numbers using previously defined mass numbers, gain ranges and detectors. A general nomenclature has evolved whereby this is spoken of as a system of up to 16 CHANNELS of PEAK SELECT.

Selection of these modes is by selecting either 'Channel' or 'Trend' from the 'Display Mode' menu.

For the CHANNEL mode the data is presented by a vertical bar for each channel representative of the measured pressure's mantissa with the associated mass, gain, detector, alarm setting, and peak height information displayed textually above it in a Channel Table. The TREND mode displays the same information, except here the graph is represented as the mantissa plotted against time for each channel of the peak select.

The settings for each channel are displayed in the Channel table. This table is made up of 5 Rows and a number of columns equal to the number of channels selected. Each column is positioned directly above the channel peak to which the information refers. The 5 rows contain the following information:

Row1. Mass

Row2. Gain

Row3. Detector

Row4. Alarm.

Row5. Peak Height.

This option allows the MASS number for measurement to be set for each individual channel. Click on the mass to be changed. The box within the table will be highlighted. At the same time a scroll bar will appear in the Change data panel located just above the channel table on the left side. The desired MASS may now be changed using this scroll bar.

This option allows the GAIN to be set for each individual channel. Click on the gain to be changed. The box within the table will be highlighted. At the same time 3 buttons will appear in the Change data panel located just above the channel table on the left side. The desired GAIN may now be changed using the up/Down buttons. The 3rd button will allow the gain to be set to auto-gain. Channels that have their respective gain in auto-gain mode can be recognised by the letter 'A' following the exponent.

Complementary with GAIN setting for each channel is the selection of the DETECTOR used for that channel. If the MULTIPLIER option has been taken then the useful gain of the mass spectrometer amplifier system is increased by 2 or more decades. The DETECTOR option allows the user to specify whether a particular channel should be measured using the FARADAY or MULTIPLIER detector. This decision should be made in conjunction with setting the GAIN for that channel and should depend on the expected partial pressure at the particular channel MASS.

This option allows the type of detector to be set for each individual channel. Click on the detector to be changed. The box within the table will be highlighted. At the same time 2 buttons will appear in the Change data panel located just above the channel table on the left side. Selecting either the Faraday button or SEM button may now change the desired detector for that channel.

Each channel has with it an associated alarm level. This is set to a number between 0 and 99 representing the first two digits of the mantissa of the partial pressure. For example if a peak is being measured on a gain range of 10-8mbar then an alarm setting of 49 will represent a level of 4.9x10-8mbar. When the measured partial pressure exceeds the alarm threshold then in CHANNEL mode the bar representing its value is coloured red, giving a readily observable indication of the alarm condition. In addition the first eight channels are equipped with relay outputs which are triggered when the alarm is tripped.

Setting the alarm level is simple. Click on the alarm setting to be changed. The box will become highlighted, and a scroll bar will appear on the change Data Panel. Now adjust the scroll bar to select the alarm threshold in the range 1 to 99.

An alarm value of 0 disables the alarm.

The bottom row on the channel Table displays the mantissa for peak height for each channel peak.

A number between 0 and 1000 represents the height, giving a readout to an accuracy of 0.1%.

This option dictates how many channels shall be measured and displayed. It can be adjusted between the limits 1 and 16 by depressing the up/down buttons to the left of the channel number display. This is positioned just above the channel table on the right. This display is only visible when in Channel or Trend modes.

There are three methods available, which are SINGLE, TIMED, and PER SCAN. They each have particular advantages that will now be described. The 'SINGLE' will send the data obtained during a single scan to disc, and is used to get one-off records of interesting results. 'TIMED' will store the data from each scan into a tempory file after a period set by the Log Interval. This can be useful for long, slow moving processes where the exact time of a change is not important. The third option, PER SCAN, follows the results of each scan. This may be best used to monitor relatively rapid changes over a short period of time. The Log Interval allows the period between data stores to be adjusted between 1 and 60 minutes. After a pre-set number of data scans the information is transferred to disc into a text file.

Leak detection can be done in a variety of ways with a variety of gases. The details are usually 'ad hoc' and so here is given only a brief introduction to leak detection.

When leak checking a normal vacuum chamber before entering LEAK DETECT mode and trying to detect the position of a leak it is nice to know that a leak exists. The easy way is to look at the BARGRAPH spectrum for 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).

If the chamber has internal water connections look for an abnormally large 18 peak indicating that a joint is broken and water is evaporating directly into the chamber.

To leak check set the QUADRUPOLE 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 chamber. If the height of the trend line increases, helium has entered the vacuum chamber and been detected by the analyser.

If the vacuum chamber has a poor conductance i.e. made of narrow tube with many bends then 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 re-spray the area where you suspect the leak. Reducing helium flow to a minimum will help to pin-point the leak site and take corrective action.

Always spray again after correction to make sure the leak has been completely eliminated.

If helium is not convenient for leak detecting your system you can use any gas, e.g. argon or CO2. To change to a different probe gas it will be necessary to change the leak detect mass. Selecting Leak Mass from the Options Menue can do this.

As with all the other operating modes the instrumental GAIN may be adjusted for the LEAK DETECT mode. Gain is adjusted from the gain display panel in the same way as in Bargraph and Analogue mode.

Leak checking may be performed using the Faraday detector or with the multiplier detector (if fitted). This option allows the detector to be set. The overall sensitivity of the QUADRUPOLE as a leak detector will be governed by the combination of the choices of GAIN and DETECTOR.

This can be selected from the opening menue.

This mode is an automated gas analysis mode. A pre-set region of the spectrum is scanned and the eight largest peaks recorded. An internal look-up table is then used to suggest the identities of the species contributing to this spectrum.

4.11. Other features.

* Some of these features are used for special applications and Engineers use and therefore user information may not be included with the instrument supplied.

1. Demo

2. Set-up 1 *

3. Set-up 2 *

4. Engineer 1 *

5. Engineer 2 *

In this mode spectra are simulated from the software and allows the instrument to be operated without an instrument connected.

It allows the user to become familiar with operation of many of the features and controls. It is also used for demonstration and training purposes.

1. Trace *

2. S.I.M. (Single Ion Monitor) *

3. T.I.M. (Total Ion Monitor) *

4. Valve Driver. *

5. Multiple Head Operation. *

6. Leak Mass

Selecting leak mass will allow other probe gases to be used for leak detection. The default mass is 4amu for helium gas. A panel will appear with a scroll bar. Adjusting the position of the scroll bar will change the default mass to any mass within the mass range of the instrument.

1. Fast Scan with display *

2. Fast Scan without display *

3. Normal Scan Mode

4. Single Scan Mode

5. Background Store.

6. Background Subtract.

In this mode the instrument will repetitively scan after selecting start.

At the end of the scan the instrument will immediately start a fresh scan and new spectral data will overwrite and update the information being displayed. This will continue until the stop button is clicked.

In this mode the instrument will do a single scan. At the end of the scan the instrument will automatically stop. It is normally used when a snapshot is required of a changing process, or when the Background store and subtract facility is used.

The BACKGROUND MODE is used to control the measurement and subsequent subtraction of the vacuum system background spectrum from the data being displayed.

From scan mode select background store.

The instrument will automatically scan over the whole mass range, and store the peak data into a temporary file, for later subtraction.

Note however, that these background stores are not held on disk and so if the power is removed from the computer or the DQC2000 software is exited, then the contents of the background stores are lost. At the end of scan a message will appear saying 'Background Stored' and the instrument will stop. The display panel will now prompt you to start background subtract when ready.

By selecting the "Background Subtract" sub-option, and then selecting start scan, the background will now be subtracted from the measured data as it is being displayed.

If the subtraction results in a negative peak then the peak is plotted as a positive peak but in red instead of blue. Background subtraction is normally used to see how much extra gas or contaminant is within the vacuum system compared to when the background was recorded. Thus at the start of measurement a background may be saved and then all subsequent measurements are taken and the background is subtracted to show the differences in measured data.

If the vacuum conditions do not change between background store and background subtract then the data will cancel and no peaks will be plotted.

Background conditions can and do change, therefore it is recommended that background storage of data is frequently updated.

SECTION 5 - RS232 COMMANDS (Software Option)

The DQC2000 remote control port is set to COM2 to allow the user to set all of the pertinent measurement variables from an external device as well as allowing the downloading of the current measured data on request. The system uses a packet communication protocol to ensure that the command sent is the one obtained. The packet also has a CRC check to ensure that the packet is not corrupted. A response is transmitted from the DQC2000 PC to all packets received. If the packet is corrupted (ie the calculated and received checksums do not agree) then a negative acknowledge is transmitted by DQC2000. On the other hand if the packet received was good then a positive acknowledgement package is sent out. This acknowledging packet may have data within it.

The command packet layout transmitted to DQC2000 is very simple and is shown diagramatically below.

_______________________________________________________________

| SOH | DATA | PACKET | COMMAND | COMMAND | CRC | CARRIAGE |

|_____|_LENGTH_| NUMBER_|_________|_PARAMETERS_|_____|_RETURN___|_

The first byte sent is the start of header indicator, SOH (ASCII 1), this is the marker used to indicate the start of the packet. The receiver process will sit waiting for this byte before getting the rest of the packet, all bytes received before this one are discarded.

The next byte is the DATA LENGTH which indicates how many command parameters are to be sent. This allows the packets to be different sizes and the system to automatically adjust to accommodate them.

The third byte in the packet is a PACKET NUMBER which it is used by the controlling computer to keep a track of the packets sent. DQC2000 does not use this byte, but it retransmits the received packet number as part of the acknowledgement packet. Thus if the controlling computer increments the packet number each time a command packet is sent to the DQC2000 then it may easily keep track of the responses. Another use would be in a system where several DQC2000 instruments are being controlled by one computer. Then each DQC2000 could be given its own packet number and the acknowledge messages would be tagged from the appropriate DQC2000.

The next byte is the command. At present there are 19 commands and a list of these will be given later along with a description of each of them.

The number of parameter bytes will depend on the command, and is indicated by the DATA LENGTH byte already described. Some commands will not have any parameter bytes, whilst others may require several bytes of data.

The last field of the packet is the checksum or CRC. The checksum is not a true CRC but is generated by adding together all the other bytes and then performing a "bitwise and" with 255. It is thus made up of the sum of all the bytes sent. This is important to appreciate since it implies that when an integer is split for transmission as more than one byte it is the generated bytes which are added to the checksum, and not the integer as a whole.

Since RS232 cannot always transfer full 8-bit numbers a protocol exists below the packet to allow 8-bit number transfers to take place. The algorithm for this is very simple. If it is desired to send an integer which is greater than 126 then it is transmitted as 127 followed by the remainder after 127 has been subtracted from it. As examples the transmissions corresponding to the integers 125 through 129 are given below.

125 - send 125

126 - send 126

127 - send 127, 0

128 - send 127, 1

129 - send 127, 2

This may be extended to transmit any positive integer by similarly splitting the second and subsequent bytes if so required. Thus the following numbers would be transmitted as indicated

253 - send 127, 126

254 - send 127, 127, 0

255 - send 127, 127, 1

256 - send 127, 127, 2

380 - send 127, 127, 126

381 - send 127, 127, 127, 0

382 - send 127, 127, 127, 1

and so on.

Below is an algorithm written in 'C'.

void rs232out(byte)

short tx;

{

void send(char); /* function to transmit a character */

while (tx > 126)

{

send(127); tx -= 127;

}

send((char)tx);

}

The reception of bytes is equally simple. If the received character is decimal 127 then keep adding subsequent characters to it until one is received which is not 127. Again an algorithm is given below in 'C.'

short rs232in()

{

char get(void); /* function to get a character */

short part, int rx=0;

do

{

part = (short)get();

rx += part;

}while (part == 127);

return(rx);

}

The acknowledging packet sent out by DQC2000 is equally simple in format. Its layout is as follows

_____________________________________________

| SOH | PACKET | ACK | DATA | CRC | CARRIAGE |

|_____|_NUMBER_|_____|______|______|_RETURN___|

if the transmission was successfully received, and

_____________________________________

| SOH | PACKET | NAK | CRC | CARRIAGE |

|_____|_NUMBER_|_____|_____|_RETURN___|

where the character ACK is the acknowledge character, 06, and NAK is the negative acknowledge, 21. In the case of a successful interchange the number of data bytes transmitted by the DQC2000 is normally 1, but may be more for some of the interrogatory commands which request measured data.

Currently all communications are done at 9600 Baud, 8 bits no parity and with 1 stop bit.

RS232 commands

Below is a list of all the commands available for DQC2000. Each command is described along with its input parameters and any returned parameters. For all these commands DQC2000 will check that the supplied parameter is legal before acting upon the command. In the event of an illegal parameter being supplied nothing will happen. The returned value is often the current value of the parameter to which the command refers. Thus if a legal value for the parameter to be set is supplied with the command, then this value is adopted and returned in the acknowledge packet, otherwise the value returned will be the value of the parameter in effect before the command was called. A short cut to check on the current setting of a particular parameter is to set it to an illegal value. In this case the returned packet will contain the current value.

In all the following descriptions the examples given assume a PACKET NUMBER of 5.

5.2 RESET (command parameter = 0)

This command is used to force an unconditional reset of the software to the same conditions as those at power up. It acts in the same way as the menu option LOAD PARAMETERS. No parameters are passed with this command. A single parameter is returned and this represents the operating mode of the instrument before the reset was given. Its value is

0 - BARGRAPH mode

1 - CHANNELS mode

2 - TREND mode

3 - ANALOG mode

4 - LEAK DETECT mode

5 - ANALYSE mode

Example - To force an unconditional reset to a DQC2000 which is operating in TREND mode:

Transmit 1 0 5 0 6

Receive 1 5 6 2 14

5.3 SET PRECISION (command parameter = 1)

This command is used to set the precision of the measurements. It directly maps to the PRECISION menu entry on the screen. One parameter, the desired precision, has to passed to DQC2000 with the command. The return parameter is the current precision after the update has been attempted.

Example - To set the precision code to 3

Transmit 1 1 5 1 3 11

Receive 1 5 6 3 15

Example - To now interrogate DQC2000 for the current precision by deliberately sending an illegal argument

Transmit 1 1 5 1 99 107

Receive 1 5 6 3 15

5.4 SET GAIN (command parameter = 2)

This command is used in two ways depending upon the operating mode set. In the modes where a single measurement gain is used (BARGRAPH, ANALOG, LEAK DETECT) then this command will set that gain. Note that the same gain is used for the BARGRAPH and ANALOG modes, but a separate variable holds the gain for the LEAK DETECT mode. For these modes the single parameter sent will determine the new gain. The actual instrument gain will depend on the collector selected. This is because the number equates to the position on the screen in the menu system. For example a gain code of 3 corresponds to 10-7 with the Faraday collector or 10-9 for the multiplier collector. Thus the true gain values will depend on the gain set and the collector selected. A table of gain code versus collector is given below.

In CHANNELS and TREND mode each of the possible sixteen channels may have its gain changed. To change the gain of a particular channel, first the channel is selected using the SET CHANNEL command, then the gain can be set using this command in a similar way to that described above. Thus the SET GAIN command sets the gain of the currently selected channel. Again the physical gain will depend on the collector selected for that channel. A table relating parameter sent to DQC2000 to detector type and actual gain is given below.

GAIN SET VALUE FARADAY GAIN MULT. GAIN

0 AUTO AUTO

1 10-5 10-7

2 10-6 10-8

3 10-7 10-9

4 10-8 10-10

5 10-9 10-11

6 10-10 10-12

7 10-11 10-13

Example - To set a gain of 10-8 on the multiplier detector

Transmit 1 1 5 2 2 11

Receive 1 5 6 2 14

Example - To set auto gain ranging

Transmit 1 1 5 2 0 9

Receive 1 5 6 0 12

5.5 SET COLLECTOR (command parameter = 3)

The collector to be used for measurement is set using this command and this, in conjunction with the gain, will determine the instrumental gain set in accordance with the table given above. In the BARGRAPH, ANALOG, LEAK DETECT, and ANALYSE modes the collector set is as per the menu entry, that is, the collector set will be the same for all subsequent measurements scan gain. In the CHANNELS and TREND modes the collector may be individually set for each of the 16 channels, just as for the gain, and so the channel has to be selected first using the CHANNEL SET command before the collector can be selected. A single parameter is required by DQC2000, which has the value 0, 1 or 2 corresponding to Faraday, multiplier, and multiplier calibration.

Example - To calibrate the multiplier

Transmit 1 1 5 3 2 12

Receive 1 5 6 2 14

5.6 SET CHANNEL (command parameter = 4)

This command is only valid in the CHANNEL and TREND modes. If it is issued when DQC2000 is operating in any other mode then a negative acknowledge packet will be issued. Otherwise this command allows selection of the channel prior to the issue of other commands to set up the measurement sequence. Thus if channel 5 (say) requires its mass and gain to be set then the SET CHANNEL command is issued with a parameter of 5, and then the set mass and set gain commands may be used. Note that the parameter passed is the channel number minus 1.

Example - To set channel 10 such that measurement are made on the multiplier at a gain of 10-8

Transmit 1 1 5 4 9 20

Receive 1 5 6 9 21

Transmit 1 1 5 3 1 11

Receive 1 5 6 1 13

Transmit 1 1 5 2 2 11

Receive 1 5 6 2 14

Example - To attempt to set the channel to 10 whilst DQC2000 is operating in LEAK DETECT mode

Transmit 1 1 5 4 9 21

Receive 1 5 21 27

5.7 SET MASS (command parameter = 5)

This command only functions in the CHANNELS, TREND and LEAK DETECT modes. If it is issued to DQC2000 whilst it is in any other mode then a negative acknowledgement will be returned. In the LEAK DETECT mode it is used to set the measurement mass and in the CHANNEL and TREND modes to select a mass for a previously set channel set. Note the comments above for dealing with masses greater than 126 which are sent as a number of bytes. The returned parameter is the value of the new mass.

Example - to set the mass of channel number 6 to 202

Transmit 1 1 5 4 5 16

Receive 1 5 6 5 17

Transmit 1 1 5 5 127 75 127 87

Receive 1 5 6 127 75 127 87

5.8 SET ALARM (command parameter = 6)

This command is only legal in CHANNEL and TREND modes and it is used to set a channel's alarm level. The first eight channels are also equipped with relay outputs which are mounted on the back of the interface card in the computer. If a measured peak moves above the alarm setting then the signal at the back of the computer is asserted and the bar on the screen changes colour. By using this command and sending the value of the alarm as a digit from 0 to 99 the alarm value may be set. 99 corresponds to full scale on the current gain range. The DQC2000 acknowledges with the current alarm setting expressed in the same way.

Example - To set the alarm level of channel 2 to 50 (half full scale on the current gain range)

Transmit 1 1 5 4 1 12

Receive 1 5 6 1 11

Transmit 1 1 5 6 50 63

Receive 1 5 6 50 62

5.9 SET MODE (command parameter = 7)

This command is used in all measurement modes to change the mode of operation of the instrument. The parameter sent is a number from 0 to 5 corresponding to the display modes as follows :-

Parameter Mode

0 BARGRAPH

1 CHANNEL

2 TREND

3 ANALOG

4 LEAK DETECT

5 ANALYSE

DQC2000 will respond with the current mode of the instrument.

Example - To select ANALOG mode

Transmit 1 1 5 7 3 17

Receive 1 5 6 3 15

5.10 SET FIRST MASS (command parameter = 8)

This command is only used in the BARGRAPH, ANALOG, and ANALYSE modes and is used to set the first mass at which scanning will take place. Since it may be wished to transmit integers greater than 127 the method of sending large numbers as a combination of bytes is used.

Example - To set the first mass to 150

Transmit 1 1 5 8 127 23 127 38

Receive 1 5 6 127 23 127 35

5.11 SET DISPLAY SPAN (command parameter = 9)

Since this parameter is always used in conjunction with FIRST MASS to set the range of scanning this command is effective only in the same modes as the FIRST MASS command, namely BARGRAPH, ANALOG, and ANALYSE. Its purpose is to set the span of the measurement scan in units of 10 mass numbers. Any span between 10 and the maximum mass can be set by this command, just as the span can be via the menu system. In the remote mode the parameter sent is the desired span divided by 10.

Example - To set a display span of 100

Transmit 1 1 5 9 100 116

Receive 1 5 6 100 112

5.12 SET FULL SPAN (command parameter = 10)

This command allows the whole of the mass range to be scanned even though not all of it is being displayed. The command is only relevant in BARGRAPH and ANALOG modes. There is a single parameter which is 0 to turn off the full span facility and 1 to turn it on. Full span is particularly useful when using RS232 control as it allows all the partial pressures to be measured whatever the DQC2000 display is set to. This ensures that any data read from the RS232 line is current.

Example - To turn the full span mode off

Transmit 1 1 5 10 0 17

Receive 1 5 6 0 12

5.13 FILAMENT CONTROL (command parameter = 11)

This command can be used in all of the DQC2000 modes. It is used to select the filaments remotely. The single parameter sent is used to determine the function. A parameter of 0 will turn off both the filaments, whilst filament 1 is turned on when the parameter is set to 1 and filament 2 is turned on with the parameter equal to 2. The return parameter is the current filament state, expressed in the same way.

Example - To turn on filament 2

Transmit 1 1 5 11 2 20

Receive 1 5 6 2 14

5.14 SET TOTAL PRESSURE (command parameter = 12)

This command may be used in all operating modes except LEAK DETECT to turn the measurement of total pressure on and off. If the TOTAL PRESSURE facility is set then at the end of each measurement scan the total pressure is measured. Enabling this option is accomplished by sending this command with a parameter of 1, and sending the command with a parameter of 0 will turn off total pressure measurement.

Example - To turn on total pressure measurement

Transmit 1 1 5 12 1 20

Receive 1 5 6 1 13

5.15 SET NUMBER OF PEAKS (command parameter = 14)

This command is only used in CHANNEL and TREND modes where it is used to select the number of channels that are being measured and displayed. The parameter sent with this command may only be between 1 and 16 inclusive.

Example - Set the number of channels to 12

Transmit 1 1 5 14 12 33

Receive 1 5 6 12 24

5.16 READ TOTAL PRESSURE (command parameter = 15)

This command may be used to read the last measured total pressure at any time and in any mode (except in LEAK DETECT). There is no parameter passed to DQC2000 but the acknowledge packet contains three data bytes. The first two bytes make up the mantissa presented as an integer between 0 and 1000, most significant eight bit byte first. The third byte is the exponent for the total pressure which is sent back as a positive number in the range -5 to -11 as per the setting of the gain range. Note that the total pressure is always measured using the Faraday detector.

Example - Reading a total pressure of 7.34 x 10-6mbar

Transmit 1 0 5 15 21

Receive 1 5 6 2 127 95 6 127 115

5.17 READ A PARTIAL (command parameter = 16)

This command is used to read a single partial pressure. In BARGRAPH, ANALOG, and ANALYSE modes the parameter passed is the mass whose partial is to be returned, whilst in the CHANNEL and TREND modes the parameter is the channel number. In all cases the returned three bytes are made up of the mantissa in the range 0 to 1000, most significant byte first, corresponding to 0 to 10V measured, and then a byte corresponding to the gain. This gain byte is automatically corrected for the detector and is a positive integer which is the modulus of the actual gain. Thus the value 2.00 x 10-8mbar would be represented by 0 200 8. This command will automatically return the most recent value of the requested partial straight away using the value stored in the memory of the DQC2000. It WILL NOT trigger a measure of that mass or channel. It is the duty of the interrogating system to ensure that measurements are currently being measured on that particular mass or channel.

Example - With DQC2000 running in BARGRAPH mode read the partial pressure at mass 32, and receive a value of 1.75x10-8mbar.

Transmit 1 1 5 16 32 55

Receive 1 5 6 0 127 48 8 127 68

Example - With DQC2000 in TREND mode read the partial for channel 4, 2.28x10-9 mbar

Transmit 1 1 5 16 3 26

Receive 1 5 6 127 101 9 127 122

5.18 READ ALL PARTIALS (command parameter = 17)

This is a global data read function, used to get the partial pressures of all the masses in the system. In CHANNEL and TREND mode each of the channels has its partial pressure returned in the acknowledge packets. Sixteen acknowledge packets are sent representing the possible sixteen channels. The format for each of the packets is as described above for reading a particular partial.

For the BARGRAPH, ANALOG and ANALYSE modes the first acknowledgement packet contains the number of masses to be reported (corresponding to the maximum mass which the instrument can measure). There then follows one packet for each of these masses formatted as above for a single partial pressure.

This command is not valid in LEAK DETECT mode.

5.19 READ MAX MASS (command parameter = 18)

This is the last command and it can be used in all modes. In BARGRAPH, ANALOG, ANALYSE and LEAK DETECT modes the DQC2000 will return the maximum mass allowed in the measurement system. In CHANNEL or TREND modes the maximum channel number (usually 16) is returned.

Example - For a DQC2000 with a maximum mass range of 300 in LEAK DETECT mode

Transmit 1 0 5 18 24

Receive 1 5 6 127 127 56 67

Example - For a DQC2000 in TREND mode

Transmit 1 0 5 18 24

Receive 1 5 6 16 28

SECTION 6 - LOGGED DATA FORMAT

The logged data is stored on the disk as an ASCII file which can be imported into most word processors or spreadsheets. The format is as follows :

The first record contains the actual mass numbers at which the measurements were made, one mass for each channel.

Subsequent records comprise the scan number followed by the partial pressures in scientific notation for each of the sixteen channels. These partial pressures are corrected for detector type.

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 erosion. 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. In the event that it is suspected that the quadrupole rods have become contaminated do not attempt to clean them without first contacting the local agent or Larimax Instruments. As the setting of the rods is critical requiring special equipment, we recommend that the analyser is returned to the factory for service. A limited procedure can be carried out on site and full details can be supplied on request.

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 DQC2000C plug from the preamplifier and check continuity from pin 7 to pin 11 (filament 1) and pin 7 to pin 9 (filament 2). The measured resistance should be 0.5 ohms or less. Check your test meter by shorting the test leads together. You will see some residual resistance caused by the test leads, therfore subtract this reading from the measured filament reading to determine actual filament resistance. If you measure a much larger 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. Depending on the model, the ion source will be accessible if a short housing has been fitted in which case proceed to section 7.2.3. If the ion source is not accessible but is within the vacuum housing proceed to 7.2.2.2.

7.2.2.2 Disconnect the 2 RF leads from the RF head, the multiplier lead from the supplies unit and the plug from the DQC2000C connector on the preamplifier. Remove the 2 screws retaining the cylindrical cover from the preamplifier. Slide the cover off. Now remove the 4 screws holding the preamplifier to the LONG pillars and partially withdraw the preamplifier. Disconnect the 4 leads to the individual ceramics and then fully remove preamplifier. The 8 bolts holding the housing to the base flange may now be carefully removed and the analyser removed from it.

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,

2. Note: The wearing of suitable gloves is very important. They should be either cotton gloves or the non-silicone ones provided in the DQC2000 spares/tool kit (If purchased).

Thoria is poisonous and radioactive! Therefore Thoria Coated Iridium Filaments Need additional precautions.

Whilst handling Thoria filaments.

DO Wear disposable mask

DO Wear disposable gloves

DO Avoid any contact with the filament surface that may dislodge the coating.

DO Safely dispose of gloves and mask after use.

DO Thoroughly wash hands when finished.

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

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 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 the tweezers. Lift the filament assembly clear of the analyser. Take the barrel connector off the filament assembly lead after first loosening the axial screw.

7.2.4.2 Check the resistance of the new filament between its leads.

7.2.4.3 Mount the new filament into the slot in the top of the analyser and secure with the fixing screws. Ensure that these screws are tight but do not over-tighten as you may damage the rod alignment. Slip the barrel connector onto the filament leg and push the long lead into the end of the barrel. This will establish the position of the barrel on the filament lead. Hold the barrel connector along its length with the needle nose pliers and tighten the screw holding the long lead. Still holding the barrel connector with the pliers, carefully manoeuvre the screw-driver and tighten the screw that is axial to the barrel connector. Before remounting the analyser in the vacuum, recheck the resistance to the outside of the feed-through.

7.2.4.4 Remount the analyser in the vacuum system using an appropriate new gasket that has been cleaned with a solvent and dried before use. Depending on the housing used, the re-assembly procedure is the reverse of the dismantling procedure.

7.3 CLEANING THE ION SOURCE.

7.3.1 WHEN TO CLEAN THE ION SOURCE.

7.3.1.1 The normal signs that the ion source may need cleaning are most evident in the analogue display mode. They are:

- gradually decreasing sensitivity

- decreasing resolution with worsening peak shape

7.3.1.2 The common physical signs are:

- ion source exterior coloured, usually blue

- ion source coated with a carbon layer

- ion source interior coated with white or yellow deposits.

The last deposit occurs when letting the analyser up to atmosphere with the filament on has blown a filament. It is also the most difficult to spot because you have to be aware of the problem or you will simply change the filament and ignore the yellow deposit on the assembly.

7.3.2 TOOLS AND MATERIALS NEEDED

7.3.2.1 The following list has many substitutes and perhaps additions:

Needle nose pliers

Tweezers

Variety of small metric wrenches (1.6mm is useful)

Lint-free tissue

Cotton or polythene gloves

Non-chlorinated solvent that must be kept in glass bottles

De-ionised water

Various clean beakers or vessels for washing

Non-ionised detergent

Set of spare ioniser insulators

Sketch pad and pencil

With a little experience you will find what works best for you. Remember the key to cleaning is cleanliness!

7.3.3 DISASSEMBLY OF THE ION SOURCE

7.3.3.1 Make notes and sketches of every step you make in the disassembly so that you can reassemble correctly. You will find your own notes to be an extremely useful aid so please do take the trouble to make them. As you remove each item, place it in order to assist in the re-assembly after the cleaning procedure.

7.3.3.2 Spread the lint free tissue on the work surface. Remove the leads to the three barrel connectors as described in section 7.2.4.1. Remove the four 1.6mm locking nuts from the top plate of the ion source together with the four insulating washers. Carefully lift the ion source top plate complete with the two filament assemblies from the body of the ion source. Remove the two filaments from the top plate by undoing the four screws.

7.3.3.3 Lift off the ion source outer cylinder and the sleeve insulators on the four threaded rods. Steady the grid assembly plate with pliers and undo the screw holding the lead in position. Remove the grid assembly plate and any other insulators.

7.3.3.4 Typically you do not have to go further into the structure than this level but take the opportunity to look carefully at the other surfaces, particularly the edges of holes through which the ions go. Look for discolouration.

7.3.3.5 If you are concerned that your analyser is contaminated beyond the degree appropriate to user rectification, then please contact your local agent or LARIMAX for details of our exchange analyser service.

** EXTREME CAUTION **

DO NOT UNDER ANY CIRCUMSTANCES TOUCH ANY PARTS WHICH HOLD THE INDIVIDUAL QUADRUPOLE RODS IN POSITION. THIS INEVITABLY LEADS TO MISALIGNMENT AND WILL COST YOU THE PRICE OF A NEW ANALYSER.

7.3.4 CLEANING THE ION SOURCE PARTS

7.3.4.1 First put the separate parts into a clean glass beaker and fill it with distilled water and some soap solution. If an ultrasonic bath is available put the beaker into it for approximately 10 minutes. After this cleaning period rinse the parts at least 4 times with distilled water.

7.3.4.2 Do not try to clean filaments. They are inexpensive, so throw away the two that you were using and fit new ones.

7.3.4.3 Do not try to clean insulators. You cannot abrade materials from their non-smooth surfaces and traditional cleaners like chromic acid usually will not attack the tungsten oxides that form the bulk of the deposits. Replace the insulators with new sets.

7.3.5 RE-ASSEMBLY OF THE ION SOURCE.

7.3.5.1 Reverse the order in which the ion source came apart. Use care and your diagrams to get the parts back in their correct places. Two common areas where problems occur are:

- interchanging the leads to the focus plate and the

source grid

- forgetting the insulators between the plates

7.3.5.2 When the ion source has been re-assembled, check the resistance between all the elements with a 20 Megohm meter. Check that each feedthrough is connected to the correct plate or rod and that the leads have not been pushed together during handling causing a short.

7.4 CLEANING THE ANALYSER RODS

7.4.1 WHEN TO CLEAN THE RODS

7.4.1.1 There are two major causes of mass filter contamination, one avoidable and the other happening as a result of use. The avoidable contamination is usually caused by incorrect trapping on an oil diffusion pump. Oil molecules find their way into the chamber containing the mass filter and coat everything. The non-avoidable contamination is caused by the ions that are not transmitted to the detector. They discharge directly onto the rods and eventually cause a reduction in sensitivity with time.

7.4.1.2 The signs that the rods may need cleaning are best seen in the analogue display mode. They are:

- gradually decreasing or low sensitivity

- decreasing resolution with worsening peak shape

7.4.1.3 The common physical signs are:

- brown or grey oval shaped ion burns just inside the entrance to the rod structure at the ion source end. They may be about 3mm long and 1mm wide

7.4.2 CLEANING PROCEDURE

7.4.2.1 The mass filter is a precision structure best left to the experts to be serviced. If you suspect that your filter is in need of attention the contact your local agent or Larimax Instruments.

SECTION 8

TROUBLE-SHOOTING

** WARNING **

HIGH VOLTAGES EXIST INSIDE DQC2000. IF YOU ARE UNSKILLED AT ELECTRONICS SERVICING, DO NOT FOLLOW ANY INSTRUCTIONS THAT REQUIRE REMOVING PANELS. IF YOU ARE SKILLED, TAKE ALL NORMAL PRECAUTIONS AGAINST ELECTRIC SHOCK WHEN SERVICING.

REMOVE THE POWER CORD WHEN WORKING INSIDE THE CHASSIS.

The first cure to try for software problems is to re-boot using

the system disk supplied with the unit.

This is achieved by switching off the power at the POWER button, waiting for a few seconds and then switching the POWER back on.

For the following sections:-

A 3 figure number e.g 8.1.1 represents the problem.

A 4 figure number e.g. 8.1.1.1 represents the cause of the problem.

A small letter e.g. a) represents a possible cure.

8.1 POWER

8.1.1 No POWER light

8.1.1.1 Power cord disconnected

8.1.1.2 Fuse blown

Replace the fuse in the back panel drawer

8.1.1.3 Bulb blown

a) Remove red lens by pulling on it. Replace bulb.

8.2 DISPLAY

8.2.1 Scrambled on Power-Up

8.2.1.1 "Glitches" in transferring software to RAM

a) RE-BOOT AS ABOVE

8.2.2 Scrambled during operation

8.2.2.1 Voltage spikes in the power line altering RAM

a) RE-BOOT AS ABOVE

8.2.3 No display

8.2.3.1 Monitor faulty

a) Test monitor on another system.

8.2.3.4 Rear connector to CRT loose

a) Check that all plugs are firmly in place.

8.2.4 Lines of display not at right angles to the chassis

8.2.4.1 Interference from an external source.

a)Check that no radiating equipment is near the monitor

8.2.5 Display "fuzzy" or jittering

8.2.5.1 Incorrect setting of line voltage selector

a) Measure line voltage and reset selector

8.3 TOTAL PRESSURE

8.3.1 Reads "0.0" and "E -10" torr

8.3.1.1 Filament "O/C"

a) See 7.2.1.1

8.3.1.2 Filament "OFF"

8.3.1.3 Scan has not reached the end of the mass range

8.3.1.4 Scanning program locked up

8.3.2 Reads low pressure compared with ion gauge

8.3.2.1 System has large partial pressure of hydrogen or helium

8.3.2.2 Emission characteristics of filament changed

a) Replace filament (common problem with thoria/ iridium filaments) - see section 7.2.2.

8.3.2.3 Ioniser voltages wrong

a) Contact local agent or LARIMAX

8.3.2.4 The ion gauge and the quad are at different pressures because of their relative positions in the vacuum chamber.

8.3.3 Total pressure is the expected value during warm-up but then drops rapidly

8.3.3.1 Vacuum conditions changing and pressure is falling.

8.3.4 Total pressure is an acceptable value but there is no spectrum

8.3.4.1 DC resolving voltage wrong

8.4 THE MASS SPECTRUM

8.4.1 No peaks in the spectra

8.4.1.1 Gain setting too low

8.4.1.2 Mass range in area where there are no peaks

8.4.1.3 Filament 'O/C'

a) See 7.2.1.1

8.4.1.4 Filament "OFF"

8.4.1.5 Multiplier is "ON" but multiplier EHT lead is not connected

8.4.1.6 Filament power supply failure

8.4.1.7 Preamp circuit fault

8.4.2 Small peaks at every mass but no proper mass spectrum

8.4.2.1 Noise spikes

Enter ANALOGUE DISPLAY and see if spikey noise is seen. Check for bad earths (grounds), power line spikes, microphony from external vibration, dirty contact to the centre collector pin. Remove the preamplifier and check the spring loaded connector for easy movement. Clean the connector with a degreasing agent if necessary.

8.4.2.2 Each mass position on the mass scale filled to the same height.

a) Preamp zero needs adjustment. Call factory for instructions.

8.4.2.3 Analyser voltages wrong

a) Contact local agent or LARIMAX

8.4.3 Full scale peaks at every mass

8.4.3.1 Bad connection between RF cable connector and control unit.

a) Reseat connector on the control unit back panel.

8.4.3.2 Gain too high

8.4.3.3 Large noise signals

8.4.4 Partial pressures of peaks too small

8.4.4.1 Gain set too low

8.4.4.2 Emission characteristics of filament changed

a) Replace filament (common with thoria/iridium filaments) see 7.2.2

8.4.4.4 Analyser voltages wrong

a) Contact local agent or LARIMAX

8.4.5 Known peaks positions wrong by 1 or 2 amu

8.4.5.1 In Analogue Display, all peak centroids progressively off with increasing mass.

a) Contact local agent or LARIMAX

8.4.6 Peaks at unbelievable masses

8.4.6.1 Operating pressure too high

8.4.6.2 Intermittent noise spikes

a) See 8.4.2.1

8.4.6.3 Peak centroids so far off that peaks appear in next mass

a) See 8.4.5.1

8.4.7 Spurious peaks at 1 amu higher than major peaks

8.4.7.1 Mass centroids out of position

a) Check with Analogue Display. Contact local agent or LARIMAX

8.4.7.2 Using too low Precision Code for the Gain setting

a) See Section 5 for suitable selections

8.4.8 In PEAK SELECT auto gain, unit hunts between two gains

8.4.8.1 Mass set in channel is one side of a large peak

a) Enter Analogue Display. Switch between the Gains that the unit is trying to establish and check if the side of a large peak is "spilling" over to an adjacent mass.

8.4.8.2 Noisy spectrum

a) Enter Analogue Display at the mass and Gain setting that Peak Select is trying to establish. Is the spectrum noisy? Change the Precision Code to a higher number and check again.

8.4.8.3 Mass centroid not correct

a) Enter Analogue Display at the mass but at low Gain so that the top of the peak can be seen. Check for the position of the centroid.

8.4.8.4 Dirty feedback resistor in Pre-amplifier

a) Contact local agent or LARIMAX

8.4.9 Rising baseline with filament off, GAIN -9 and PC 3

8.4.9.1 Auto zero failure

8.4.10 First Bar Graph scan is good but the second loses small peaks

8.4.10.1 Dirty feedback resistor in Pre-amplifier

a) Contact local agent or LARIMAX

8.5 FILAMENTS

8.5.1 Filaments "OFF" and won't switch "ON"

8.5.1.1 Software problem

a) REBOOT AS ABOVE

8.5.2 Filaments show "O/C" when switched on

8.5.2.1 Filaments #1 and #2 blown

a) See section 7.2.1.1

8.5.2.2 Analyser voltages wrong

a) Contact local agent or LARIMAX

8.5.2.3 Filaments intact but thinned due to operational wear

a) Replace filaments see section 7.2.2

8.5.2.4 Filament power supply failure

a) Contact local agent or LARIMAX

8.5.3 Filament "ON" but no spectrum or total pressure

8.5.3.1 Multiplier is 'ON' but the multiplier EHT lead is not

connected

8.5.3.2 Connection between the RF Generator and Analyser is poor

8.5.3.3 Analyser voltages wrong

a) Contact local agent or LARIMAX

8.5.3.4 Filaments intact but thinned due to operational wear

a) Replace filaments see section 7.2.2

8.5.3.5 Filament power supply failure

a) Contact local agent or LARIMAX

8.5.3.6 Collector (pin 10) to preamplifier connection is poor

a) Switch off, remove the preamplifier and check the alignment of centre pin on the analyser. Push the spring loaded collector pin on the preamplifier and check for easy movement. Clean the connector with degreasing agent if necessary.

8.6 MULTIPLIER

8.6.1 Multiplier will not calibrate

8.6.1.1 EHT cable not connected to the Control Unit

a) If cable present, check continuity with an Ohmmeter

8.6.1.2 The amplitude of 28 is too high

a) Enter Analogue Display and check that the apex of 28 amu is below 5 x 10-8 torr GAIN as measured with the Faraday detector.

8.6.1.3 Multiplier failure

a) Contact LARIMAX or your local dealer

8.7 PRINTER

8.7.1 Garbled across full page

1. Check with your supplier that the printer has graphics capability .
2. Reboot computer with printer connected.
3. Check correct printer driver selected for printer in use.

8.7.1.3 Run the printer's own internal diagnostics

8.8 VOLTAGE CHECKS AND REPAIRS

8.8.1 The DQC2000 is a complex unit. As different models have very differing characteristics, it is not possible to provide detailed instructions for the investigation of electronics problems in a manual of this type. Should an electronics problem be suspected, then contact your local agent or LARIMAX for advice. A detailed investigation procedure will be provided according to the nature of the problem. Do not remove covers from the electronics units before contacting the agent or LARIMAX.

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