MKS 937B - Setup a Hot Cathode Sensor

MKS 937B Operation Manual
41
cathode gauge from operating at high pressure, thereby extending the service life of the cold
cathode sensor. Valid Control Setpoint values range from 5x10
-4
to 1x10
-2
torr for a Pirani,
and from 2x10
-3
to 1x10
-2
torr for a Convection Pirani gauge. The default Control Setpoint
value is 5x10
-3
torr.
If the controlling gauge (PR/CP) and cold cathode gauge are connected to the
same chamber, ensure that the control SP is less than 5x10
-3
torr; otherwise, the CC
sensor may be damaged due to high operating pressure. The CC sensor may be turned
off by the Protect Setpoint function.
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.
When the power of PR/CP is turned off, or the cable is unplugged, the CC will be
turned off if the control setpoint is enabled.
A capacitance manometer cannot be used to control the cold cathode gauge.
To set the Control SP, first select the control channel (Dir/Ch). Once a valid channel has
been selected, the Control SP function can be enabled. There are three choices:
 AUTO: the high voltage for a cold cathode gauge is controlled solely and
automatically by the controlling gauge (PR/CP). However, if the protection
setpoint is triggered, the auto control will be disabled, and the CC sensor can
only be turned on manually.
 SAFE: the high voltage for a cold cathode gauge can be automatically turned off
by the controlling gauge; however, it can only be turned on manually. This keeps
the cold cathode sensor from being turned on at high pressure, especially, when
the controlling gauge is not properly set.
 OFF: Even if the control channel is selected, it will not be activated. The cold
cathode must be turned on/off manually.
12. Cold cathode board with fast relay output
When fast control using a cold cathode sensor is required (<15 msec), a cold cathode board
with fast relay output control is available. This fast control is achieved by comparing the
buffered analog output signal with an internal DAC output determined by a serial command
(@254FRCn!d.ddE-ee;FF, where n is the channel number (1, 3, 5), and d.ddE-ee is the
pressure setpoint value). The comparator controls an opto-isolated solid state relay, which
enables the fast control of an external device.
6.5.5 Setup a Hot Cathode Sensor
Refer to Figure 6-11 for setting up a Hot Cathode sensor.
1. Gas Type