937A Multi-Sensor System
A.8
To disassemble the Sensor, remove the backshell subassembly as follows
(Steps 1 through 4 are not necessary when replacing internal parts):
1
Remove the two
4-40 x ¼" Phillips head SEMS screws and slide
the
backshell off the sensor.
2
Remove the two
4-40 x ¼" button head screws .
3
Use needle nose pliers to pull the
#22 contact carefully off of the
ion current feedthrough .
4
Pull the
#20 contact off of the 5kV feedthrough taking the entire
bulkhead with it (do not remove the SHV and SMA connectors
from the bulkhead).
5
Remove the six
¼-28 x 0.875" socket head cap screws and pull
the back
flange free. Note that these screws are silver-plated for
lubricity and should be used only once. They may be relubricated with
a dry lubricant such as molybdenum disulfide, though new silver-
plated screws are recommended. The
copper gasket must be
replaced with a standard 2
1
/8" CF flange gasket.
The cathode and anode assemblies are attached to the flange. Here
disassembly generally proceeds from bottom to top of the internal
assembly drawing.
6
To remove the
cathode , release the two integral, spring-loaded
ears hooked over the shoulder of the
ceramic insulating support .
7
Gently pull up on the ear until it just clears the outer diameter of the
insulating support.
the position of the small Elgiloy
®
leaf used to connect the
ion
current feedthrough to the cathode. Rotational position of the
cathode with respect to the leaf is not critical, but take care to not
bend the
leaf.
8
Slide the
cathode and washer off the insulating support.
9
The
insulating support is captured by the guard bolt . Remove
with a spanner wrench and unscrew the
guard bolt from the flange .
the presence of the small curved
spring washer under the head of
the
guard bolt. The spring washer holds the insulating support tight,
preloads the
guard bolt to resist unscrewing due to possible vibration,
and provides compliance for differential thermal expansion during bakeout.
Cleaning the Series 421 Sensor
The procedure for cleaning the internal parts of the 421 sensor is the same as
that used for the Series 423 I-MAG Cold Cathode Sensor (see p. A.3).
22
18
23
21
13
24
19
23
7
8
4
10
17
17
2
9
1
20
13
