MKS UniMag 971, Operation And Installation Manual, Page: 34 / 44

971 UniMag ™ Operation manual 31
If a Cold Cathode sensor is turned on and operated at pressures higher than 1.0E-3 Torr, material from the
high voltage anode can be sputtered to the inside walls of the cold cathode transducer. Inert gases like
argon are easier to ionize and consequently the sputter effect is more significant in such environment.
If material is sputtered from the anode to the inside wall, of the transducer the pressure measurement will
typical be lower than actual pressure. Sputtering can also be visually detected since the inside wall of the
transducer changes color. When operated in oil lubricated pumping systems, hydrocarbons can cause
contamination of cold cathode measuring cell. Contamination will normally cause a lower pressure reading
than actual pressure. The cold cathode hour counter can be used to determine if service is required. If
sputtering occurs, the anode module can be changed from the flanges side without disassembling of the
transducer. The anode module (p/n: 970-ANODEKIT) is available as spare part. The basic accuracy of the
cold cathode sensor can change after change of anode. The anode module can also be cleaned by
mechanical polishing.
970 Series anode module
Do not touch anode module, screen, screws or clip ring by hand. If items are accidental touched by
hand, use alcohol to clean items.
Changing the 971 anode module
1. Turn power off and remove cable.
2. Dismount the transducer from the vacuum system.
3. Remove the clip ring (1) using a clip ring remove/insert tool (p/n: 100017193).
4. Remove the screen (2).
5. Unscrew the three Torx (T6) screws (3) at the anode module (4).
6. Remove the anode module (4).
7. Insert the new anode module (Do not touch module).
8. Insert the screws (3), but DO NOT tighten. After all screws are inserted carefully tighten the screw a
little and move on to the next one. Continue to tighten the screws one by one until all tight.
9. Insert the screen (2) and clip ring (1).
10. If a leak detector is a available, perform leak testing