Ulvac GI-M2, Инструкция по эксплуатации

Страница: 80 / 101

74
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Measurement value drifts.
Possible cause Corrective action
Sensor head is contaminated or
sensitivity has lowered
markedly.
Change the sensor head with another one and check
the symptom. If there is no problem with another
sensor head, the problem is in the sensor head now
used.
Sensor head cable is vibrating. If the sensor head cable is always subjected to
vibration, the indicated value may drift because of
the friction electromotive force in the sensor head
cable. Re-examine the method of laying the cable.
Sensor head cable is
electromagnetically induced (by
external noise).
Check the place of laying the sensor head cable or
make check by turning off a component that can be a
source of noise. If the sensor head cable is
responsible, re-examine the method of laying cable.
Also examine measures against noise.
Line voltage is fluctuating. Check line voltage by a circuit tester. (line voltage:
100 VAC
±
10 V)
Filament is turned ON above
the measurable pressure range.
Check pressure using a Pirani gauge or other vacuum
gauge. If the pressure is too high, gas cannot be
ionized normally and the ion current generated will
apparently be on the same order as that when
pressure is low. Thus, the filament protecting
function is not activated.
GND potential is fluctuating.
Check control ground and ground of the sensor head
mounted position by a circuit tester or oscilloscope.
Take actions to improve the GND wiring or install
the controller or sensor head afloat.
Sensor head cable has blown out
or insulation failure has
occurred, resulting in leakage
current.
Check insulation between electrodes of the sensor head
cable using a Megger. Also check continuity across the
connector using a circuit tester. (See page 89
～
.)
Note: After checking the ion collector (coaxial contact)
for insulation using a Megger, short the portions
checked with Megger by means of a jumper wire.
If the cable is connected to the sensor head
without shorting them, the sensor head may fail.
If the cable is found defective, replace or repair it.
Insulation failure has occurred
between electrodes of the sensor
head or leakage current has
occurred.
Check insulation between electrodes of the sensor head
and the outside wall using a Megger. (Megger
indication should be infinite.)
(See page 86.)
If insulation failure is confirmed, replace the
sensor head with a new one.