946 Controller Instruction Manual
pg. 115
11.1.2.3 Assemble the Series 431/422 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 over tighten 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.
11.1.2.4 Preparing the Sensor for Bakeout
To prepare a Series 431 sensor for bakeout up to 125°C, remove the high voltage and ion current cables
only. Series 431 sensors can be baked up to 250 C after the backshell subassembly is removed. Refer
to section 11.1.2.1 above, and follow steps 1 to 4 for the backshell subassembly removal.
The bakeout temperature of a fully assembled Series 422 sensor depends upon the exact catalog part
number of the sensor. Some versions are limited to 100°C with the backshell attached, others 250°C.
Series 422 sensors with high temperature connectors 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.
11.1.2.5 Testing a Cold Cathode Sensor
MKS 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.
11.2
Maintenance of Series 423 I-Mag Cold Cathode Sensor
11.2.1 Disassemble the I-Mag Sensor
1. Clean tweezers and clean smooth-jaw, needle-nose pliers are required.
2. Turn OFF the power to the 946 Controller.
3. Loosen the thumbscrew on top of the sensor cable and remove the cable. After safely
venting/backfilling the vacuum system, remove the sensor from the system.
4. Loosen the two
flat head screws
15
. See Figure 11-4.
5. Remove the magnet
14
.
6. Using the smooth-jaw, needle-nose pliers, firmly grab the compression spring
3
at the tip
closest to the flange.
7. Pull on the compression spring
3
while rotating it to free it from the formed groove of the
sensor body
9
. Continue to pull until the compression spring
3
is completely free.
8. With the vacuum port facing up, carefully remove the remaining components (
4
through
8
)
from the sensor body.