GA130001441_002_C0
– 09/2016
11
3.
General Equipment Description
3.1
COMBIVAC CM 51
This combination instrument offers three measurement channels, two THERMOVAC and
one PENNINGVAC. Thus measurements and checking of vacuum pressures over 12 full
decades from 1·10
-9
to atmospheric pressure is possible. Six switching thresholds permit the
integration of the COMBIVAC CM 51 within complex vacuum control facilities. The two
THERMOVAC channels are immediately active upon powering up. The PENNINGVAC
channel may be switched on and off by one of the two THERMOVAC channels or externally
or manually. The operating status of the switching thresholds and the measurement systems
is displayed and signalled correspondingly through the outputs.
3.2
THERMOVAC (Pirani) Method of Measurement
This method of measurement covering the range of 5·10
-4
to 1·10
3
mbar utilises the heat
conductance of the gas for the purpose of measuring its pressure. In order to attain a
response time which is as short as possible, all THERMOVAC instruments rely exclusively
the principle of the controlled Pirani where the measurement filament is part of a Wheatstone
Bridge. When the temperature of the filament changes due to pressure changes, then the
bridge is unbalanced. The quickly responding control circuitry adapts the heating power for
the filament so that the filament temperature again reaches its nominal level thereby
balancing the measurement bridge again. The displayed pressure is dependent on the type
of gas. By default the display of the instruments has been calibrated for nitrogen,
respectively air.
3.3
PENNINGVAC (cold cathode) Method of Measurement
For the purpose of measuring the pressure, a high tension is applied to the sensor thereby
igniting a gas discharge. The thus produced ion current is output by way of a signal which
is proportional to the pressure. This sensor arrangement allows assured and reliable
measurement operation of the cold cathode in the range from 1·10
-9
mbar to 1·10
-2
mbar.
Two each versions with KF and CF flange are available.
3.4
Connectable Gauge Heads
The following gauge heads can be operated by the COMBIVAC CM 51:
Gauge heads
Type
THERMOVAC
TR 211, TR 212, TR 216
PENNINGVAC
PR 25, PR 26, PR 27, PR 28
Table 2
–
Connectable gauge heads
