MKS 937B Operation Manual
37
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.
6.5.4 Setup a Cold Cathode Sensor
Please refer the Figure 6-10 for setting a Cold Cathode sensor.
1. Gas Type (GT)
To move the cursor to the Gas Type box, press
Enter
, then use the or keys to select the
correct gas type for the sensor. Three gas types (N
2
, Ar and He) can be selected. Default setting
for Gas Type is N
2
.
2. User Input Calibration Gas Correction Factor (U Cal)
This allows the user to enter different correction factors for cold cathode sensors. This function is
useful, when the calibration gas used is not one of these listed above (N
2
, Ar or He). The valid
range is 0.1 to 50, and the default setting is 1.0.
3. AO Delay
The Analog Out Delay function prevents the activation of the cold cathode sensor's setpoint
relays and maintains their outputs in the OFF state until the delay has expired. The range is from
3 to 300 seconds and the default value is 3 seconds. When the AO delay is active, WAIT will be
displayed on the front panel rather than a pressure reading.
4. Fast Relay SP
To meet the requirement for fast control of vacuum system (such as to close a valve rapidly to
protect an UHV system), a special cold cathode control module with a fast relay control is
available. The response time is typically less than 3 msec, and the control setpoint for this fast
relay is set via the Fast Relay SP described here. The hysteresis is approximately 15% of the
setpoint value, that is, the relay will be re-energized when the system pressure is 15% below the
setpoint. The default setpoint value is 1x10
-5
torr.
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