Thyracont VSH88D, Руководство по эксплуатации

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vsh-de-130326
4 Operation
4.1 General
Measurement Principle
The VSH vacuum transducer is equipped with an internal combination sensor of
type Pirani / Hot Cathode.
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.
The hot cathode sensor of Bayard Alpert type ionizes gas molecules by electron
bombardment. The resulting ion current is a measure for the number of gas
molecules present in the sensor and proportional to the absolute pressure.
Output Signal
The output signal 1.219 - 8.6 V of your VSH has a logarithmic dependence on
pressure over the whole measurement range 5.0x10
-10
- 1000 mbar.
Conversion of voltage signal and pressure is done according to the following
formula:
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 VSH 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 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.
V
out
/V = 0.6 log (p/mbar) + 6.8
p /mbar = 10
( (Vout /V – 6.8) / 0.6 )