HELIX GRANVILLE-PHILLIPS Convectron ATM, Instruction Manual

Page: 36 / 98

Chapter 3
28
Convectron
®
ATM Vacuum Gauge Module Instruction Manual
If you are using Figure 3-10 or Figure 3-11, find the point at which the
horizontal line representing the desired trip point for N
2
or air pressure
intercepts the vertical line representing test point voltage. For example:
• in Figure 3-10, a test point voltage of 0.64 V represents an N
2
or air
pressure of 40 mTorr.
• In Figure 3-11, a test point voltage of 4.8 V indicates an N
2
or air
pressure of 40 Torr.
If the gas being used is not included in Table 3-5, or for a gas mixture,
you will need to generate a calibration curve using a gas-independent
transfer standard such as a capacitance manometer.
3. Use a high-precision, high-input impedance (Z
in
> 1 M
Ω
) digital
voltmeter (DVM) to measure the voltage across the SETPOINT1 and
COMMON or SETPOINT2 and COMMON test points on the module
front panel. Figure 3-9 illustrates SETPOINT2 and COMMON test
points.
4. Use a flat-head instrument screwdriver to adjust the SETPOINT1
potentiometer for the desired setpoint voltage at which relay 1 will
activate and deactivate. (See Figure 3-9.)
5. A built-in 30 mV hysteresis prevents oscillation around the setpoint.
Hysteresis depends on the vacuum chamber pressure at which the
setpoint has been established.
Figure 3-9 Test points and potentiometer for setpoint relay 1
COMMON test point SETPOINT1 test point
SP1 ADJ potentiometer