946 Controller Instruction Manual
pg. 66
7 Installing Vacuum Sensors
7.1 Installing Cold Cathode Sensors
Verify that the vacuum port to which the CC sensor is moun ted is electr ically
grou nded. It is essential for person nel safety as well as prope r operation that the
envelope of the sensor be connected to a facility grou nd.
Be aware that an electrical disch arge throu gh a gas may couple dangerou s hi gh voltage
dir ectly to an ungrou nded con ductor almost as effectively as would a cop per wire
connection. Perso nnel may be seriously injur ed or even killed by merely touching an
exposed ungrounded conduct or at high potential. This hazard is not uni que to this
prod uct.
7.1.1 Locating a Cold Cathode Sensor
Locate Cold Cathode sensors in a position suitable for the measurement of process chamber or manifold
pressures. Install the sensor away from pumps, gas sources, and strong magnetic fields to ensure the
most representative data. Place and orient the sensor such that contamination is minimized. For example,
if a sensor is installed directly above a diffusion pump oil vapor can contaminate the cathode, anode, and
other vacuum wetted components, causing calibration drift.
7.1.2 Orienting a Cold Cathode Sensor
A Cold Cathode sensor can be installed with the body set in any direction. The operating position does
not affect accuracy. As with any sensor, installation with the vacuum port facing down is preferable since
this helps to prevent contaminants from falling into the sensor.
7.1.3 Managing Contamination in a Cold Cathode Sensor
Do not operate a Cold Cathode gauge at pressures above 10
-3
Torr for extended periods. This will
increase the likelihood of contamination due to higher sputtering rates. If pressure readings appear
erratic, the sensor may be contaminated. In such a case, the it should be visually inspected and, if
contamination is visible, the internal components should be cleaned or replaced using an Internal Rebuild
Kit.
7.1.4 Connecting the Series 431/422 Sensor
Mount the sensor to a grounded vacuum system. KF 25 or KF 40 flanged sensors must be attached with a
conductive, all-metal clamp to ensure the sensor body is grounded. On sensors with CF flanges, a ground
lug on a flange bolt could be used to attach a ground if necessary.
Connect the cables to the sensor and to the Controller before turning ON. Connections on the rear panel
of the Controller are H.V. (SHV connector) and Ion Current (BNC connector). The sensors also have H.V.
and current connections. Note that some Series 422 sensors have LEMO connectors rather than SHV
and BNC connectors.
If there is any potential for strain on the cable, use separate strain relief to avoid damage to the sensor,
cable, or the Controller.
Cables are available from the factory in standard lengths of 10, 25, 50, and 100 feet and in custom
lengths up to 300 ft.