Operation; General - thyracont VSP63D Betriebsanleitung

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4

Operation

4.1

General

Measurement Principle
VSP and VCP vacuum transducers are equipped with an internal Pirani sensor.
The Pirani principle uses the heat conduction of gases for measuring vacuum.
A sensor filament in a Wheatstone circuit is heated to a constant temperature, so
the bridge voltage is a measure for total gas pressure.
Output Signal
The output signal 1.5 - 8.5 V of your VSP (VCP: 2.2 - 8.5V) has a logarithmic
dependence on pressure over the whole measurement range 1x10
(VSP) or 5x10 - 1000 mbar (VCP).
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Conversion of voltage signal and pressure is done according to the following
formula:
V /V = log (p/mbar) + 5.5
out
p /mbar = 10
Serial Interface RS485
The measured absolute pressure can be read out digitally via the transducers
serial RS485 interface. Additionally you can set various parameters like gas
correction factors or setpoints. For further information see chapter 5 communica-
tion.
Warm-Up Time
The signal output of the transducer is available approx.. 2 s 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 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. In accordance, the accuracy can
be reduced in the range below 10
Dependence On Gas Type
The output signal depends on composition and type of the gas being measured.
The unit is adjusted for N
Pirani sensor can be set via RS485 (see chapter 5.8. This results in a correct
pressure display below 0.1 mbar.
VSP-de-171005
( Vout /V – 5.5 )
mbar.
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and dry air. For other gases correction factors for the
2
The output voltage characteristic can
be scaled by software command, see
chapter 5.8.
- 1000 mbar
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