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Page 15
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Maintenance
D023-92-880 Issue F
5
Maintenance
CAUTION
Do not clean the interior of the gauge tube as you can damage the filament.
You can replace the sintered filter and its retaining circlip on 'NW' flange tubes. On
1
/
8
inch NPT tubes the sintered
filter cannot be replaced.
5.1
Atmosphere and vacuum adjustment
Every APGX-H gauge is individually calibrated before shipment however thermal conductivity gauges in general can
drift with time or as contamination builds up on the filament. Use the procedures outlined below to adjust the
vacuum and atmosphere settings of the APGX-H. The frequency of which they should be repeated will vary depending
on the level and nature of contamination associated with the process. The atmosphere adjustment is particularly
important if the APGX-H is installed in any orientation other than vertical or if the orientation is changed.
5.1.1
Atmosphere adjustment
1. Switch on the power supply to the APGX-H and allow it to operate for at least 10 minutes. Ensure that the green
status LED is lit.
2. With the vacuum system at atmospheric pressure, press the '
CAL
' switch. The status LED will flash red and the
voltage output of the gauge will read approximately 9 V. If the APGX-H is connected to an Edwards AGC, TIC or
AGD, the display will read approximately 1000 mbar (750 Torr).
5.1.2
Vacuum adjustment
1. Reduce the system pressure to 1 x 10
-5
mbar (7.5 x 10
-6
Torr) or below and allow the gauge to operate for at
least 10 minutes.
2. Press the '
CAL
' switch. The status LED will flash red and the voltage output will read approximately 1.9 V. If the
APGX-H is connected to an Edwards AGC, TIC or AGD, the display will read 0.0E-4 mbar (0.0E-4 Torr).
Every time '
CAL
' is pressed, the new calibration values are stored inside the tube. If the tube is then transferred to
a different electronics housing, the latest values stored inside the tube will automatically be used.
If required, the factory calibration values can be recalled by performing a factory values reset. Refer to
.
5.1.3
Atmosphere adjustment at pressures other than 1000 mbar (750 Torr)
If the barometric pressure is known, it is possible to adjust the gauge to read the atmospheric pressure rather than
the default value of 1000 mbar (750 Torr). The gauge can be adjusted for barometric pressures between 700 mbar
(525 Torr) and 1100 mbar (825 Torr).
Use the '
CAL
' push button switch to adjust the APGX-H.
1. Switch on the power supply to the APGX-H and allow it to operate for at least 10 minutes.
2. With the vacuum system at atmospheric pressure, press and hold the '
CAL
' switch for more than five seconds.
The voltage output of the gauge will begin to decrease in steps of approximately 10 mV. Release the '
CAL
' switch
just before the desired voltage is reached. To make finer adjustment, release the '
CAL
' switch and immediately
depress the switch as many times as required. If the switch is released for more than four seconds, the value will
be stored. When the output reaches around 8.85 V, the voltage will quickly ramp up to around 9.04 V. The
output will then ramp down slowly. Refer to
for formulae to convert output voltage to pressure).