Veeco MS40 Operation And Maintenance Manual page 90

7. Re-select the TEST PORT function. Verify that the test port
pressure is still the same as recorded in Step 4. If the reading has
changed, repeat the procedure until the fore-line pressure and test
port pressure match.
Calibration of the High Vac Gauge. (The test port Pirani calibration must be
verified first according to the manual)
The high vacuum "gauge" in an MS40 is an integral part of the source in these
machines. It replaces the Discharge Gauge formally used, which was easily
contaminated by improper running.
It works by monitoring the beam of ions that is generated in the source. This beam
is accelerated into the magnetic field for separation to detect helium. The top
plate, which previously was a ground plate that accelerated the ions now is
isolated and monitored by a "meter" circuit. The ions at the edge of the beam
strike this plate and are collected and amplified to provide a means of measuring
the total pressure in the spectrometer.
As there are small physical differences from source to source this current will not
be exactly the same for each machine and must be calibrated. This is done
initially at the factory but may have to be re-calibrated when filaments are
replaced or the source is rebuilt. The procedure follows:
1. Make sure that the MS-40 is in the Service Mode, the filament is off, the
source is disconnected and only the foreline valve is open.
2. Open the vent valve. Install a closed variable leak valve in the test port.
Close the vent valve.
3. Close the foreline valve . Open the rough valve.
4. When the test port pressure reads 20 mTorr or less, open the fine/direct
valve, then open the foreline valve. Close the rough valve.
5. Make sure the filament is still off. Plug in the source connector.
6. Slowly open the variable leak until the test port pressure is reading 23 to
28 mTorr (use the digital readout of test port pressure on the display.)
7. Select Hi Vac. on the alphanumeric display. Turn on the filament.
8. Adjust the high vacuum pressure reading to 4.7 to 4.9X10-4 Torr using the
only potentiometer on the B Board.
1109-186-00 Rev. C 4-21