937B Controller Instruction Manual
pg. 38
11. Control SP
The Control Set point is used to turn the Cold Cathode sensor on or off with a higher-pressure
sensor, typically a Convention Pirani, Convectron or a Capacitance Manometer (must be
≤2 Torr
full scale). This prevents the cold cathode from operating at high pressure, extending the service
life. The adjustable Control SP range depends upon the sensor used for control.
2x10
-3
to 1x10
-2
Torr for a Convection Pirani or Convectron sensor
5x10
-4
to 1x10
-2
Torr for a Pirani
0.2% of full scale to 2x10
-2
Torr for capacitance manometer (
must be ≤2T f.s.)
The default Control Set Point value is 5x10
-3
Torr. Extended operation of the cold cathode at
higher pressures will shorten the CC
sensor’s lifetime.
When the power to a PR/CP used as a control sensor is turned OFF, or the cable is
unplugged, the CC will be turned OFF if the control set point is enabled.
When a capacitance man
ometer (must be ≤2T f.s.) is used to control a cold cathode
sensor, it is recommended to enable the AUTOZERO of capacitance manometer as a zero
shift of the manometer may cause the control function to occur a higher actual pressure,
possibly damaging sensor.
The 1x10
-2
Torr upper limit can be extended to 9.5x10
-1
Torr by using a
@254XCS!ON;FF serial command in special situations such as when the PR/CP/CM and
CC are installed at different locations. For example, when the PR/CP/CM is installed on the
foreline between the mechanical and turbo pumps monitoring the mechanical pump
pressure, and the CC is installed on the high vacuum chamber.
To set the Control SP, first select the control channel in the box under the Dir/Ch heading. Once
an allowed channel has been selected, the Control SP can be enabled. There are three choices:
•
AUTO: The high voltage for a cold cathode is controlled solely and automatically by
the controlling sensor. In
AUTO
it will be tuned both ON and OFF by the control
sensor as appropriate. However, if the protection set point is triggered, the auto
control will be disabled, and the CC sensor can then only be turned ON manually.
•
SAFE: The high voltage for a cold cathode sensor will be automatically turned OFF
by the controlling sensor and remain OFF until the CC is turned ON manually.
•
OFF: The Cold Cathode must be turned ON/OFF manually. Even if a control channel
is selected, the CC will not be turned ON or OFF.
6.5.5
Setup a Hot Cathode Sensor
Refer to Figure 6-11 in setting up a Hot Cathode Sensor.
1. Gas Type
To change the gas type, move the cursor to the
GT
box, press ENTER, and use the UP or
DOWN arrow keys to select the gas type in use with the sensor. Four gas types (N
2
, Ar, He and
Custom
) can be selected.
When N
2
, Ar, and He are selected, the corresponding gas correction factor is displayed on the
right-hand side of the
Gas Type
box, and this value cannot be modified. However, when
Custom
is selected, a customized gas factor can be entered, ranging is from 0.1 to 50.