Off After Low Emission vacuum error on the AutoSpec - WKB55829

SYMPTOMS

• Ion gauge "Off After Low Emission" error message appears in Tune Status and Vacuum Control page
• Cannot switch on the ion gauge; no vacuum reading is possible

ENVIRONMENT

• AutoSpec Ultima (M)
• AutoSpec Premier (P)

CAUSE

The ion gauge filament is open circuit or shorting to ground or shorting to the grid.

FIX or WORKAROUND

1. Check the resistance of your meter leads before making any measurement; touch the black and red measurement leads together.
   • The resistance reading should be very low—optimally, less than one Ohm.
2. Measure the resistance between pins 7 and 8 on the ion gauge end flange.
   • 
3. Expect to see a resistance less than 1 Ohm, take into account the resistance of the meter leads as above. This would show the filament is good.
4. If the resistance is very high/infinite or open circuit, the filament has failed and must be replaced.
   • Part number for the Ion Gauge Filament: 7991802 - IR23 FILAMENT (VIG 8)
   • Part number for the complete Ion Gauge Assy:  700012500 - GAUGE ION VIG 8 KF40
5. If the resistance is good (less than 1 Ohm), suspect a grounded internal filament (short circuit).
   • Check if Ion Gauge peak display fault disappears when disconnecting the ion gauge cable. If this occurs then problem is probably due to shorting filament to grid.
6. Measure the resistance from either pin 7 or pin 8 to the instrument housing/ground.
7. Expect to see a high, open-circuit resistance. This is the normal condition.
   • A low resistance indicates a short circuit, which needs to be rectified.
8. The ion gauge must be removed following all vacuum handling procedures, and the short must be cleared by carefully adjusting the filament.
   • NOTE: Never touch the ion gauge filament with bare hands. The filament is thorium-coated and mildly radioactive.
   • It is possible that no resistance will be seen when you make the measurement to ground. The filament may be in close proximity to the instrument housing, making a real connection only when voltage and current are supplied.
   • If the Analyzer region shows the error, test both ion gauges for a short to ground.
   • Disconnect the Analyzer 2 ion gauge connector (BB350), and try to turn on the Analyzer 1 ion gauge. If a reading is seen, the problem is in the Analyzer 2 ion gauge.
   • Likewise, disconnect the Analyzer 1 ion gauge connector (BB150), and try to turn on the Analyzer 2 ion gauge. If a reading is seen, the problem is in the Analyzer 1 ion gauge. 

ADDITIONAL INFORMATION

See article WKB96022 on how an ion gauge works.