937B Controller Instruction Manual
pg. 35
10. DIR
DIR determines when the relay is activated. If ABOVE is selected, the relay will be activated
when the pressure is above (greater than) the set point. If BELOW is selected, the relay will be
activated when the pressure is below (less than) the set point. The default setting for DIR is
BELOW.
See Figure 8-1 and Section 8.1.2 for more a detailed description of the DIR setting.
11. 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
-3
to 9.5x10
+2
Torr for Convection Pirani sensors and 2x10
-3
to 9.5x10
+1
Torr for
Pirani sensors. The speed of the value change can be increased by continuously pressing the UP
or Down arrow keys.
12. Hyst
When a set point value is changed, the hysteresis value will be changed automatically. If DIR is
set to ABOVE, the hysteresis will automatically be set to 0.5xSet point; if DIR is set to BELOW,
the hysteresis is automatically set to 1.5xSet point.
To modify the hysteresis, move the cursor to the hysteresis value, press ENTER and use the UP
or DOWN arrow keys to change the value, then press
ENTER again to set the value. The
maximum hysteresis value permitted for PR/CP gauges is 0.9xSet point when DIR is set to
ABOVE; the minimum hysteresis is 1.1xSet point when DIR is set to BELOW.
13. Power Control of a Convection Pirani or Pirani Sensor
Pirani or Convection Pirani gauges can be turned ON or OFF using the Power ON/OFF key.
Note that when a pyrophoric gas is encountered (such as during the degeneration of a cryo
pump), it is strongly recommended that the power of the Pirani, CP or Convectron be turned OFF
to avoid any potential for ignition of the gas.
The power to these sensors should also be turned OFF when the sensor
’s cables are
disconnected to avoid any potential for sensor damage.
“Hot Swaps” should be avoided.
If the power for a Pirani or Convection Pirani is turned OFF while it is controlling (in either AUTO
or SAFE) a hot or cold cathode sensor, the HC or CC will be switched OFF immediately. To avoid
this, disable the control of the HC or CC sensor first before powering OFF a Convection Pirani or
Pirani sensor.
When the power to a CP, Convectron, or Pirani sensor is turned ON, a time delay is added before
activating control or relay set points. This helps to avoid turning ON a controlled hot or cold
cathode sensor at high pressure due to any transient and inaccurate pressure indication that may
occur during the power-up.
6.5.4
Setup a Cold Cathode Sensor
Refer to Figure 6-10 for the Cold Cathode Sensor set up screen.
1. Gas Type (GT)
To change the gas type, move the cursor to the
GT
box, press ENTER, then use the UP or
DOWN arrow keys to select the gas type in use with the sensor. Three gas types (N
2
, Ar, and He)
can be selected.