MKS Granville-Phillips 358 series, Instruction Manual

Page: 98 / 122

Chapter 6
98
Series 358 Micro-Ion Controller Instruction Manual - 358013 - Rev. B
6.4 Special Considerations
for Use Below 10
–3
Torr
During a fast pumpdown from atmosphere, thermal effects will prevent the
Convectron gauge from tracking pressure accurately below 1 x 10
–3
Torr.
After about 15 minutes, indications in the 1 x 10
–4
range will be valid and
response will be rapid.
In the 1 x 10
–4
Torr range, the indication is accurate to about
±
0.1 milliTorr
provided the instrument has been carefully zeroed at vacuum. See Gauge
Zero and Atmospheric Pressure Adjustment on page 81 for vacuum and
atmosphere calibration procedures. For accurate use in the 1 x 10
–4
range,
zeroing should be repeated frequently.
Convectron pressure readings in the 1 x 10
–4
Torr range may differ from
those of the ion gauge, since ion gauges usually lose sensitivity near their
upper pressure limits.
6.5 Gauge Electrometer
Operation Figure 6-3 Electrometer Module Front Panel
Displaying Sensitivity
with Calibration Switch
The CAL switch is used for displaying pressure or gauge sensitivity. It is
activated by setting to the ON position. The data displayed will depend on
the state of the Micro-Ion Gauge tube:
If the Micro-Ion Gauge is OFF, setting the switch ON displays the Micro-Ion
Gauge sensitivity in the display. This will be in scientific notation. If the
Micro-Ion Gauge is ON, the switch has no effect and pressure will be
displayed.
NOTE: Do NOT leave the calibration switch in the ON
position after viewing the sensitivity - otherwise, the
displayed reading might be mistaken for the actual pressure
reading.
Emission Range Switch
The emission range switch selects between three emission ranges; 20
microamperes (MV), 1 milliampere (HV), or 4 milliamperes (UHV).