937B Controller Instruction Manual
pg. 40
3. DG Time
Length of time for a degas cycle of a hot cathode sensor. The value can be set from 5 to 240
minutes in 1-minute increments. The default value is 30 min.
4. Sensitivity
The sensitivity value in use with the hot cathode is displayed. For a definition of sensitivity, see
Section 11.3.1.
Nominal Sensitivity values are 9 Torr
-1
for the MKS Low Power Nude sensor, and 12 Torr
-1
for
the Mini BA sensor. These values will be automatically selected based on the type of sensor
detected on power up, if no user-defined sensitivity value has been stored. Sensitivity values
from 1 to 50 Torr
-1
can be entered from the front panel or over communications.
Once a user-defined sensitivity is saved, this value will become the default value when powering
up the same type of hot cathode.
If a sensitivity is entered without a hot cathode being connected, this user-defined sensitivity
value will be saved as the default sensitivity for all the HC sensor types.
5. EC
The Emission Current can be set to 20 uA, 100 uA, Auto20, or Auto100. When Auto 20 or
Auto100 is selected, the emission current is either 20 uA or 100 uA respectively when the
pressure is higher than 1x10
-4
Torr, and automatically switched to 1 mA when pressure is below
1x10
-4
Torr.
6. Protect SP
The Protect Set Point is turns off the hot cathode operating voltages based on its own pressure
readings. The Protect Set point is always enabled on the 937B but can be set within the range
1.0x10
-5
Torr to 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 hot 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.
7. Relay
Each Hot Cathode module has four preassigned relays as shown below. The controller auto-
detects the correct relays corresponding to where the HC module is installed.
Module location
A1
B1
C1
Relay assigned
1 & 2 & 3 & 4
5 & 6 & 7 & 8
9 &10 & 11 & 12
8. Enable
There are three ways to enable a relay:
•
SET: force the relay to activate (close) regardless of pressure and set point values
•
CLEAR: force the relay to deactivate (open) regardless of pressure and set point values.
•
ENABLE: relay status is determined by the pressure, set point value, and direction.