MKS 937B - Page 38

MKS 937B Operation Manual
38
 SET: forces the relay to stay in the activated state (closed) regardless of pressure
and setpoint values
 CLEAR: forces the relay to stay in the deactivated state (open) regardless of
pressure and setpoint values.
 ENABLE: the relay status is determined by the pressure, setpoint value, and
direction.
10. DIR
DIR determines when the relay is activated. If ABOVE is selected, the relay will be activated
when the pressure is above the setpoint (higher than the setpoint pressure). If BELOW is
selected, the relay will be activated when the pressure is below (less than) the setpoint. The
default setting for DIR is BELOW.
Refer to Figure 8-1 for more a detailed description of the direction setting.
11. SET SP
This function allows input of the desired setpoint value. The valid range is 2x10
-3
to 9.5x10
+1
torr for Pirani gauges, and 2x10
-3
to 9.5x10
+2
Torr for Convection Pirani gauges. The speed
of the value change can be increased by continuously pressing the
or key during the
setting change.
12. Hyst
When the setpoint value has been changed, the hysteresis value will be changed
automatically. If DIR is set to ABOVE, the hysteresis will automatically be set to 0.5xSetpoint;
if DIR is set to BELOW, the hysteresis is automatically set to 1.5xSetpoint.
To modify the hysteresis, move the cursor to the hysteresis value, press
Enter
and use the
or keys to change the value, then press
Enter
again to set the value. The maximum
hysteresis value permitted for PR/CP gauges is 0.9xSetpoint when DIR is set to ABOVE; the
minimum hysteresis is 1.1xSetpoint when DIR is set to BELOW.
13. Power control of a Pirani or Convection Pirani sensor
Power to the Pirani or Convection Pirani gauges can be turned on or off using the Power
On/Off push button.
Note that when a pyrophoric gas is encountered (such as during the degeneration of cryo-
trap), it is strongly recommended that the filament power of the Pirani or convection Pirani
sensor be turned off to avoid any potential for ignition of the gas.
The power to the Pirani sensor should also be turned off when sensors are “hot swapped” to
avoid any potential for sensor damage.
If the power for a Pirani or convection Pirani is turned off while it is controlling (either AUTO
or SAFE) an ion gauge, the ion gauge will be switched off immediately. To avoid the ion
gauge being turned off at high vacuum (especially, for a cold cathode gauge which may take
long time to start at UHV), it is recommended to disable the control of the ion gauge first
before powering off a Pirani or convection Pirani sensor.
When the power to the Pirani is turned on, a time delay is added to avoid having an ion
gauge being turned on at high pressure when a potential inaccurate transient pressure
indication may occur while the power-up for PR/CP sensor is in progress.