MKS 937B - 12.2 I-MAG Cold Cathode Sensor Maintenance

MKS 937B Operation Manual
112
12.1.2.3 Assembling the Series 421/422 Sensor
To reassemble the sensor, reverse the order of procedures used during disassembly. Note the
following tightening procedure for the guard bolt. The bolt has a 3/8" 40 thread design that is delicate.
1. Finger tighten the guard bolt to compress the spring washer and then back off one
turn. Do not overtighten as this will remove all compliance from the spring washer
and possibly damage the aluminum
3
/8"-40 thread.
2. Verify that the anode
14
is well-centered within the bore of the guard bolt.
3. If it is off center, carefully bend it back into position and continue with the assembly.
12.1.2.4 Preparing the Sensor for Bakeout
The 421/422 sensor, including the LEMO connectors in the bulkhead, will withstand bakeout up to
250°C. Additionally, the sensor may be operated during bakeout if cables and connectors with
appropriate temperature ratings are used. Cables or connectors rated to temperatures less than the
bakeout temperature need to be disconnected from the sensor for bakeout. In applications requiring
repeated bakeouts, the use of bakable connectors and cables is suggested. To prepare the sensor
for bakeout up to 125°C, remove the high voltage and ion current cables only.
12.1.2.5 Testing a Cold Cathode Sensor
HPS cold cathode sensors contain anode and cathode (collector) electrodes. Test the sensor with an
ohmmeter. There should be no shorts between the electrodes or from the electrodes to the sensor
body.
12.2 Maintenance of Series 423 I-MAG
®
Cold Cathode Sensor
12.2.1 Connecting the I-MAG Sensor
Mount the Sensor to a grounded vacuum system.
If the I-MAG Sensor has a CF flange, remove the magnet to allow clearance for bolt installation.
When replacing the magnet, note that it is keyed to the sensor body to protect the feedthrough pins
from damage. The pins should be straight and centered.
For grounding, use a conductive, all-metal clamp to mount a KF 25 or KF 40 flanged sensor body.
Connect the cable to the sensor and to the 937B Controller before turning on your system. Tighten
the thumbscrew on top of the cable to make sure it is securely in place.
12.2.2 Disassembling the I-MAG Sensor
1. Clean tweezers and clean smooth-jaw, needle-nose pliers are required.