'' 2.
,.
IG Set Point Adjust (power on)
I.
Rotate the set point pot fully CCW.
2.
Allow pressure in the system to stabilize at the desired control point.
3.
Slowly rotate the pot CW until the process relay energizes.
The process control relays on the ionization gauge are interlocked in the following
manner:
I.
Operation is only possible when the autorange switch is in the on position.
2.
The filament relay must be energized for a period of two seconds to allow for
filament turn on and to create an electrometer output.
Pin information for the IG process relay output is given in Section 3. In order to
prevent oscillation around the trip point there is a built-in hysteresis effect amounting to
approximately 15% of a decade. For example, if a set point is established to pull in a relay at
5 x 10-6 it will not drop out until the pressure rises above 6.5 x 10-6.
The process control relays may be used separately or together to suit your specific
application. Two examples are shown in Fig. 4-2 and Fig. 4-3.
Fig. 4-2 can be used to allow a process to operate over a specific pressure band. In t.!;ie
example shown the process would only be allowed if the system pressure is between 5 x
IO
-7
Torr.
Fig. 4-3 can be used to control a process where a large pressure rise is expected once
the process is initiated. In the example shown the process would begin when the pressure
decreased to 5 x I0-7Torr and remain on as long as the pressure remained below 5 x 10-6
Torr.
4.6 Filament Operation
Starting the Filament (Manual Mode)
CAUTION: Gauges with tungsten filaments may be damaged by attempting to operate
the filament in active gas atmospheres at pressures greater than about
I
x 10-3 Torr.
I.
When operating the controller for the first time or with a system at an unknown
pressure, set the autorange switch either to on or to off in
I o-4
range.
2.
Momentarily toggle the filament switch to the on/off position and observe the
following events.
3.
The ionization gauge filament should glow. Note that the tungsten filament glows
much brighter than a thoria coated iridium filament when operated at the same
emission current.
4.
The red filament LED should come on and stay on. NOTE: The filament LED will
not stay on if the required electron emission current is not attained within
approximately I second after the filament switch is depressed. Common causes of
no emission are:
A.
B.
C.
D.
Gauge cable not connected
Pressure in tube is too high
Open filament in tube
Grid shorted
4-5
