Thyracont VSP63, Operating Instructions Manual

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VSP63-de-120207
4 Operation
4.1 General
Measurement Principle
The VSP63 vacuum transducer has an internal Pirani sensor, which uses the
heat conduction of gases for measuring vacuum. A sensor filament is heated to a
certain temperature threshold in pulsed mode, the time needed for heating is a
measure for total gas pressure.
Output Signal
The output signal 1,5 – 8,5 V of your VSP63 has a logarithmic dependence on
pressure over the whole measurement range 1,0x10
-4
- 1000 mbar (1V per
pressure decade).
Conversion of voltage signal and pressure is done according to the following
formula:
Warm-Up Time
The signal output of VSP63 is available immediately after the unit is switched on.
To take advantage of the maximum accuracy of the unit it is appropriate to allow
for stabilization time of 2-5 minutes, especially when extreme pressure changes
have occurred.
Accuracy
The unit is adjusted ex works in upright position and at 24V voltage supply.
Through contamination, ageing, extreme climatic conditions or different mounting
orientation the need for readjustment may arise. Accuracy is reduced in the
range above 20mbar and below 10
-3
mbar.
Dependence On Gas Type
The output signal depends on composition and type of the gas being measured.
The unit is adjusted for N
2
and dry air. With He and CO deviations will be almost
negligible below 0.5mbar. For other gases the pressure display can be corrected
below 0.5 mbar when the VSP63 is operated with a Thyracont display unit.
Correction factor (to be multiplied with the uncorrected pressure reading):
Ar
1,6 H2 0,57 Ne 1,4
CO 1,0 He 1,0 Kr 2,4
CO2 0,89 N2 1,0
V
out
(V) = log (p(mbar)) + 5.5
p (mbar) = 10
(Vout(V) - 5.5)