10
Affected by moisture and dirt
Attach the gauge head to a location as unaffected as
possible
Influenced by heat of vaporization by gradual
vaporization.
There is a leak in the gauge head or the area where
the gauge head is attached
Gauge head leak
⇒
Replace the gauge head
Other leaks
⇒
Stop the leak
Bad cable contact, increased wire resistance
Check the cable connection and resistance.
The cable is affected by electromagnetic induction.
(By external noise)
Change the cable installation location. Use this unit
with the device generating the noise turned off.
Review how the cables are installed
Examine separate measures for noise
●
The pressure is changing but the pressure reading is stable.
Cause
Action
The power supply voltage to the SH2 is not the
specified range
Check the power supply voltage with a tester.
The pressure is below the specified range
Normal
The pressure is above the specified range
Normal
Nearby noise source
The CPU may be frozen
⇒
Cycle the power.
●
The expected pressure and measured pressure greatly differ
Cause
Action
The gauge head is dirty
Sensitivity has dramatically deviated
Replace the gauge head with another gauge head and
check the phenomena. If there is no problem with the
other gauge head, the gauge head was the problem.
Measuring air at the nitrogen setting.
This is normal.
When air is measured at the nitrogen setting, a
pressure 60% higher is shown.
Environment with a large amount of moisture or oil Attach the gauge head to a location as unaffected as
possible
Influenced by heat of vaporization by gradual
vaporization.
The actual pressure differs
Check with another pressure gauge.
5.2.
Checking for a filament break
！
注意
There is a risk the filament may break if a current of 2 mA or higher passes through
it. Take note of the current value for the measurement instrument.
Overcurrent to the filament
In a vacuum, the filament is heated and an accurate resistance value cannot be
measured, so always measure at atmospheric pressure.
The Pirani vacuum gauge head filament is wired as shown in the figure below. Check continuity
referring to this figure. The filament's resistance is approximately 13
Ω at atmospheric pressure.
2 mA or lower
Approx. 13 Ω
(Under atmospheric pressure)
Figure 6-1 Gauge head filament wiring diagram
