Operation; General - thyracont VSR53D Betriebsanleitung

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4

Operation

4.1

General

Measurement Principle
The VSR vacuum transducer is equipped with an internal combination sensor of
type Piezo / Pirani.
Under the influence of pressure the thin diaphragm of the piezo-resistive sensor
is bent, on its back a resistor-bridge is applied. The bending forces the
measurement-bridge to come out of tune, which is a measure for the applied
pressure.
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 - 8.58 V of your VSR has a logarithmic dependence on
pressure over the whole measurement range 1x10
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 4.2 communi-
cation.
Warm-Up Time
The signal output of VSR 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 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
VSR-de-170116
( Vout /V – 5.5 )
-2
mbar.
-4
- 1200 mbar.