937B Controller Instruction Manual
pg. 41
9. DIR
To prevent the Hot Cathode from being turned ON at high pressure, the DIR for a Hot Cathode is
permanently set to BELOW.
Refer to Figure 8-1 and Section 8.1.2 for a more detailed description of the direction setting.
10. SET SP
SET SP displays the entered and saved set point trip value. To change the value, scroll to the
value to be changed, highlight by pressing ENTER, and then adjust to the desired value with the
UP or DOWN arrow keys. Confirm the change by pressing ENTER. The set point pressure can
be between 5x10
-10
to 5x10
-3
Torr. When entering the value, the speed of the value change can
be increased by holding the UP or DOWN arrow keys while changing the value.
11. Hyst
When a set point value is changed, the hysteresis value will be changed automatically. Since the
direction is set to BELOW for the Hot Cathode sensor only, the hysteresis will automatically be
set to 1.5x Set point.
To modify the hysteresis, move the cursor to the hysteresis value, press ENTER, use the UP or
DOWN arrow keys to change the value, and press ENTER. to set the value. The minimum
allowed hysteresis for the Hot Cathode is1.1x Set point when direction is set to BELOW.
12. Control SP
The Control set point is used to turn the Hot Cathode 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 hot 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
•
5x10
-4
to 1x10
-2
Torr for a Pirani
•
0.2% of full scale to 2x10
-2
Torr for a Capacitance Manometer (≤2T full scale)
•
The default control set point value is 5x10
-3
Torr. Extended operation of the Hot Cathode at
higher pressures will shorten the H
C sensor’s lifetime
When the power to a PR/CP used as a control sensor is turned OFF, or the
cable is unplugged, the HC will be turned off if the control set point is enabled.
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
HC 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 HC is installed on the high vacuum chamber.
When a capacitance man
ometer (must be ≤2T f.s.) is used to control a Hot Cathode,
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 the sensor.
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. Three options are
available:
•
AUTO: The filament for a hot 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