MKS 937B - Page 44

MKS 937B Operation Manual
44
9. DIR
To prevent the hot cathode from being turned on at high pressure, the DIR for a hot cathode
is permanently set to BELOW.
Refer to Figure 8-1 for a more detailed description of the direction setting.
10. SET SP
Enables setting of the desired setpoint value. The valid range is 5x10
-10
to 5x10
-3
. To speed
up the value change, hold the
or key.
11. Hyst
Once the setpoint value is changed, the hysteresis value will be changed automatically. Since
the direction is set to BELOW for the hot cathode sensor only, the hysteresis will be set to
1.5xSetpoint automatically.
To modify the hysteresis, move the cursor to the hysteresis value, press
Enter
, use the or
key to change the value, and press
Enter
to set the value. The minimum allowed
hysteresis for the hot cathode is1.1xSetpoint when direction is set to BELOW.
12. Control SP
The Control setpoint is used to turn on or off the hot cathode gauge using a reference gauge,
typically a Pirani or a Convention Pirani. This prevents the hot cathode gauge from operating
at high pressure, and therefore extends the service life of the hot cathode sensor. The valid
control setpoint value is from 5x10
-4
to 1x10
-2
torr for a Pirani, and from 2x10
-3
to 1x10
-2
torr
for a Convection Pirani. The default control setpoint value is 5x10
-3
torr.
If the controlling gauge (PR/CP) and hot cathode gauge are connected to the
same chamber, make sure the control SP is less than 5x10
-3
torr, otherwise the HC
sensor may be damaged due to high operating pressure. The HC sensor can be turned
off by the protect setpoint setting.
The 1x10
-2
torr upper limit can be extended to 9.5x10
-1
torr by using a
@254XCS!ON;FF serial command to cover the condition when the PR/CP and CC are
installed on different location. For example, when the PR/CP is installed on the foreline
between the mechanical and turbo pumps (being used to monitor the mechanical
pump pressure), and the CC is installed on the high vacuum chamber downstream of
the turbo pump.
The capacitance manometer cannot be used to control the hot cathode gauge.
To set the Control SP, first select the control channel (Dir/Ch). Once a valid channel is
selected, enable the Control SP. Three choices are available:
 AUTO: The filament power for a hot cathode gauge is controlled solely and
automatically by the controlling gauge (PR/CP).
 SAFE: The filament power for a hot cathode gauge can be turned off by the
controlling gauge automatically, however, it can only be turned on manually. This
prevents the hot cathode sensor from being turned on at high pressure,
especially when the controlling gauge is not set properly.
 OFF: Even if the control channel is selected, it is not activated. The hot cathode
sensor must be turned on/off manually.