© Edwards Limited 2020. All rights reserved. Page 15
Maintenance
D14643880 Issue L
5 Maintenance
CAUTION
Switch off the power supply before removing the gauge from the vacuum system. High voltages exist internally
in the gauge. The connecting cable should be removed before attempting to dismantle the gauge.
5.1 Dismantling the body tube
The body tube assembly can be removed from the gauge by gripping the magnet housing and twisting the body tube
flange anti-clockwise to unlock the bayonet fitting. The tube can then be completely withdrawn from the gauge
electronics/magnet housing.
The electrode can be removed from the body tube for cleaning or replacement as follows:
With reference to Figure 5, using the flat spanner provided with the spares kit (see Section 7.2), locate the two lugs
in the end of the collar and rotate anti-clockwise to completely unscrew. Once the collar is removed the anode
assembly and O-ring can be withdrawn.
The cathode plate and tube are removed from the flange end of the body tube by releasing the circlip using a pair
of circlip pliers. Note the correct orientation of the plate and tube. The cathode plate should be closest to the collar
end of the body tube.
Re-assembly is the reverse procedure taking care not to bend the anode and ensuring that it is centralised in the body
tube when tightening the threaded collar.
5.2 Bayonet fitting of body tube
Refer to Figure 5.
A. Insert body tube fully into magnet and electronics housing.
B. Rotate the body tube clockwise relative to the magnet housing to lock the body tube into position.
C. The end cap can be rotated relative to the magnet housing. This allows for a variable socket orientation.
5.3 Cleaning
The anode assembly has a stainless steel bracket mounted close to the disk on the anode. The gap between the disk
and the bracket should be maintained at 0.25 mm minimum and can be adjusted using a fine screwdriver or feeler
gauge. The gap should be cleaned by running a strip of fine emery paper between the bracket and the disk.
Note: Failure to maintain the gap will impede the gauge striking performance.
The cathode plate, cathode tube, body tube and anode assembly can be cleaned by firstly degreasing in a proprietary
degreasing agent, and then thoroughly soaking in a laboratory detergent. After soaking the parts should be thoroughly
rinsed in clean water and then in methanol to remove all traces of water. The parts should be dried thoroughly.
WARNING
If the electronics are disconnected from the body tube and the body tube is left connected to a
vacuum system, then if a plasma discharge is maintained in the system in the vicinity of the body
tube, the anode and guard ring of the body tube assembly may become charged up.
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