Edwards AIM-SI1-NW25, Instruction Manual, Page: 18 / 26

D146-71-880 Issue E
Page 14 © Edwards Limited 2015. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Maintenance
5.3 Replace the electrode assembly
CAUTION
Internal anode assembly includes a sharp-edged component. Care should be taken when handling this item.
Refer to Figure 4 in the following procedure.
1. Remove the AIM Gauge from the vacuum system as described in Section 5.2.1 .
2. Remove the body tube from the AIM Gauge as described in Step 1 of Section 5.2.2 .
3. Fit the flat spanner supplied in the electrode assembly kit (refer to Section 7 ) to the two lugs in the end of the
collar (1), then turn the collar anticlockwise to unscrew the collar from the body tube (4) and remove the anode
assembly (2) and the O-ring (3).
4. Use circlip pliers to remove the circlip (8) from the vacuum flange end of the body tube, then remove the outer
cathode plate (7), cathode tube (6) and the inner cathode plate (5).
5. Fit the new inner cathode plate (5) into the body tube (4) ensuring the end with reduced diameter is furthest
from the vacuum flange. Then fit both new cathode tubes (6). If this has been done correctly the second
cathode tube will now be protruding about 2 mm beyond the end of the vacuum flange. Hold the outer tube so
that the inner cathode plate is held in place, invert the assembly, and rest the outer cathode tube on the bench.
6. Fit the new O-ring (3) and anode assembly (2) into the body tube.
7. Refit the collar (1) to the body tube. Locate the flat spanner on the two lugs on the collar and turn the collar
clockwise until it is fully secured in the body tube.
8. Hold the outer tube so that the inner cathode plate is held in place, and re-invert the assembly so that the
14-point striker on the anode can be seen. Remove and discard the outer cathode tube.
9. Now use the 0.5 mm diameter wire supplied to check that the minimum gap between the striker and the inner
cathode plate is at least 0.5 mm. This means ensuring the wire is able to pass between the striker and cathode
plate all the way round. If not, use a single (gloved) finger on the top of the anode to gently bend it in the
appropriate direction. Repeat the test and gentle bending if necessary until the striker-cathode plate gap
is 0.5 mm.
10. Fit the new outer cathode plate (7) and secure with the circlip (8). Ensure both the circlip centre and ends are
pushed tight towards the inner cathode plate.
11. Refit the tube assembly to the magnet housing as described in Step 2 and 3 of Section 5.2.2 . Refit the vacuum
gauge to the vacuum system as described in Section 5.2.3 .
5.4 Replace the electronics and magnet housing
The magnet housing and end-cap contain the AIM Gauge control electronics. Replace the complete unit as described
below.
1. Remove the AIM Gauge from the vacuum system.
2. Remove the body tube from the AIM Gauge.
3. Dispose of the old magnet housing and end cap (refer to Section 6 ).
4. Fit the body tube to the new magnet housing and end-cap. Refit the AIM Gauge to the vacuum system.