937B Controller Instruction Manual
pg. 37
5. Protect SP
The Protect Set Point feature will turn OFF the Cold Cathode high voltage at the specified
pressure. The Protect Set Point range for a Cold Cathode is 1.0x10
-5
Torr to 1.0x10
-2
Torr. The
default value is 5.0x10
-3
Torr. It can be disabled by continuing to press UP key when the set point
value reaches 1.0x10
-2
Torr.
Once the Protect Set Point is triggered and the sensor turned OFF, the auto control
via the Control SP is disabled. The gauge can only be turned back on manually or by serial
command. When control mode is used, the Control SP should be set to a pressure lower
than the Protect Set Point to ensure the cold cathode is controlled by the higher-pressure
sensor. Tripping of the Protect Set Point may indicate that the control set point is not
functioning properly, such as due to a control sensor malfunction or both sensors are not
connected to the same volume.
6. Relay
Each Cold Cathode module has four preassigned relays as shown below. The 937B controller
auto-detects the correct relays corresponding to where the CC module is installed.
Module location
A1
B1
C1
Relay assigned
1 & 2 & 3 & 4
5 & 6 & 7 & 8
9 &10 & 11 & 12
7. Enable
There are three ways to set a relay:
•
SET: forces the relay to stay in the activated (closed) state regardless of pressure and set
point values
•
CLEAR: forces the relay to stay in the deactivated (open) state regardless of pressure and
set point values.
•
ENABLE: the relay status is determined by the pressure, set point value, and direction.
8. DIR
The DIR (Direction) for relays actuated by a cold cathode are permanently set to BELOW. The
relays are closed whenever the pressure is below the set point.
See Figure 8-1 and Section 8.1.2 for more a detailed description of the direction setting.
9. 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 2x10
-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 key.
10. Hyst
When a set point value is changed, the hysteresis value will automatically be changed. Since the
direction is always set to BELOW for Cold Cathode sensors, the hysteresis will be automatically
set to 1.5x set point.
To modify the hysteresis, move the cursor to the hysteresis value and press ENTER. Use the UP
or DOWN arrow keys to change the value, then press ENTER again to set the value. The
minimum hysteresis value for a Cold Cathode is 1.1xSet point; DIR is set to BELOW at all times.