Thyracont VCP63E, Operating Instructions Manual

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VSPE-de-171117
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 measured absolute pressure can be read out digitally via the transducers
serial RS485 or via EtherCAT interface. Additionally you can set various parame-
ters like gas correction factors. For further information see chapter 5.
Warm-Up Time
The transducer's signal output 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 2 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
-2
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. For other gases correction factors for the
Pirani sensor can be set via RS485 (see chapter 5.7). This results in a correct
pressure display below 0.1 mbar.