47
VSM-de-171005
Cathode Control (CC)
For certain vacuum processes it may be favoured to suppress the automatic start
of the cold cathode sensor, which is usually controlled by the transducer
electronics. Therefore it is possible to disable the cold cathode by software
command "Cathode Control" (CC) via RS485 interface:
"0": disabled cold cathode sensor remains switched-off
"1": enabled (Default) start of cold cathode is automatically controlled
When the cold cathode is disabled your VSM behaves like a Pirani transducer
with range 1000 - 1x10
-4
mbar.
Below 1x10
-4
mbar the serial interface sends a "ur" signal for underrange, the
analog output remains at a voltage corresponding to 1x10
-4
mbar.
Parameter " Cathode Control" is only temporarily saved in the
transducer memory. After mains supply is switched off or dis-
connected the parameter will be reset to "1" and the cold cath-
ode enabled !
Gas Correction Factor C1 / C4
The output signal of the VSM depends on type and composition of the gas being
measured. The unit is adjusted for N
2
and dry air. For other gases the pressure
display can be corrected below 0.1 mbar by setting correction factors for both
sensor types via RS485.
The measurement results of both sensors are then individually multiplied with the
corresponding correction factors by the units microcontroller. The VSM can
thereby provide a corrected pressure signal as analog and digital output.
Value range: 0.20 … 8.0
Correction factor C1 Pirani:
Ar 1,6 CO
2
0,89 He 1,0 Ne 1,4
CO 1,0 H
2
0,57 N
2
1,0 Kr 2,4
Correction factor C4 Cold Cathode:
Ar 0,80 H
2
2,4 N
2
1,0 Kr 0,6
CO
2
0,74 He 5,9 Ne 3,5 Xe 0,41
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