MKS HPS 903 Series, Operation And Maintenance Manual

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14
Cold Cathode Ionization Vacuum Sensor
The set point can be turned off by connecting pin 7 (set point disable) to pin 4
(power supply input (-)).
If the high voltage is started in high vacuum and the sensor
discharge has not yet begun, the (IMT) will indicate too low of a
reading, possibly tripping the set point. In this case, you should
deactivate the set point, monitor the reading until the sensor
starts, and activate the set point thereafter.
Venting to Atmosphere
While the (IMT) can withstand rapid venting to atmosphere without damage,
prolonged operation at pressures above 10
-3 Torr increases the negative
effects of contamination in the sensor. Contamination can result in
measurement errors and, in severe cases, instabilities requiring more frequent
cleaning of the (IMT).
Analog-to-Digital (A/D) Converter
To take full advantage of the (IMT’s) capabilities, an A/D converter with an
input voltage span of 0 to 10 V may be used. A resolution of 12 bits is
needed, corresponding to 2.44 mV per bit. The A/D converter should have a
differential input to ensure accurate measurements.
Preparing for Bakeout
Shut off power to the (IMT) and remove its cable. Remove the two Phillips
head screws holding the electronics assembly to the sensor body. The
remainder of the Sensor is ready to be baked out to 400°C if using a CF
flange or to 150°C if using a KF flange.
Leak Detection
Its inherent sensitivity to gas type makes the Series 903 (IMT) useful for
detecting leaks in vacuum systems. It is a good complement to a mass
spectrometer leak detector, which locates smaller leaks.
Probe the suspected leak areas with a gas that has an ionization potential
different than that of the system gas. Helium or argon gas is suitable for
probing a system pumping air or nitrogen.