Series 360, Granville-Phillips, Stabil-Ion, Ionization, Vacuum ...

6 Service and Maintenance
6.5 Electrometer Minimum Calibration Adjustment
This test and adjustment should only be done with the cover on and securely fastened to the
Control Unit. This adjustment is used to cancel residual input currents so that the logarithmic
electrometer amplifier is accurate in its lowest decades. It performs the same function as the zero
adjustment on a conventional electrometer even though there is no zero reading on a log amplifier.
It is factory set by calibrating the pressure readout to correspond to a very small collector input
current. It can be checked in the field without a calibration source using the following procedure:
1. Verify that the scale factor is adjusted to 1.00.
2. Operate a Stabil-Ion Gauge with 4 mA emission (low pressure range).
3. Disconnect the collector lead from the rear panel of the electrometer module.
4. Observe the display for 10 seconds as it settles to a
minimum reading. This reading should be between
2.50 x 10 -11 and 2.75 x 10 -11 Torr.
5. Locate the MIN. ADJ control on the rear panel of the
Electrometer Module. See Figure 6-3.
6. Generate a display between 2.50 x 10 -11 and 2.75 x 10 -11
Torr by making very small adjustments of less than 1/4 turn
at a time. It will be difficult to achieve a stable reading
because of electronic noise at very low input currents. The
optimum point is where the control causes the display to
just switch to its minimum reading of 2.50 x 10 -11 Torr.
IG1
IG2
ELECTROMETER
COL.
1 19
R
E
M
O
T
E
9 26
COL.
MIN.ADJ.
ANA.
OUT
Figure 6-3
Rear View, Electrometer Module
Showing MIN. ADJ Control.
6.6 Flashing Degas Light
If the DEGAS LED flashes when degassing with cathode 1 selected, but stays on continuously with
cathode 2 selected, this is an indication that only cathode 1 is in poor condition and will eventually
fail to maintain normal operating emission. When this occurs, the IG will fail to stay on with
cathode 1 selected, and you will need to switch to cathode 2 for normal operation. If the same
condition occurs after you have switched to cathode 2, it may indicate that the gauge needs to be
replaced, or that there is a contamination source affecting both cathodes. See Step 6. on page 5-2
for more discussion.
6-6
Series 360 Stabil-Ion December, 2001