Chapter 3
36
Convectron
®
ATM Vacuum Gauge Module Instruction Manual
3.6
Calibrating Convectron
gauge at vacuum
chamber pressure
Periodic resets of the vacuum chamber calibration point improve the
accuracy and repeatability of the Convectron gauge.
Regardless of the process gas that is being used, you should always use N
2
or air to calibrate the Convectron gauge at vacuum chamber pressure.
1.
Turn on the pump and, using N
2
or air, allow vacuum chamber
pressure to descend to a pressure that is lower than 10
–4
Torr.
2.
Refer to Figure 3-17 and use a high-precision, high-input impedance
(Z
in
> 1 M
Ω
) DVM to measure the voltage across the CONVECTRON
ANALOG and COMMON test points on the module front panel.
3.
Use a flat-head instrument screwdriver to adjust the CONVECTRON
ADJUST VAC potentiometer to a reading of 0.375 VDC.
Figure 3-17 Vacuum chamber pressure calibration test points and potentiometers
3.7
Modules operating below
10
–3
Torr
During a fast pumpdown from atmospheric pressure, thermal effects
temporarily prevent the module from measuring pressure accurately below
10
–3
Torr. After approximately 15 minutes, pressure indications the 10
–4
Torr range will be accurate and response will be rapid.
When pressure indication in the 10
–4
Torr range has stabilized, a
Convectron gauge calibration at vacuum chamber pressure may be
performed. The calibration may be performed at a higher pressure if
readings in the 10
–4
Torr range are not required. In the 10
–4
Torr range,
resolution is ±0.1 millitorr, if the Convectron gauge has been properly
calibrated at vacuum chamber pressure. If the module frequently operates
in the 10
–4
Torr range, Convectron gauge calibration at vacuum chamber
pressure should be performed frequently.
CONVECTRON ADJUST
VAC potentiometer
COMMON
test point
CONVECTRON ANALOG
test point
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