IMC CANSAS - General Remarks; Absolute and Relative Pressure; Barometer

P8 pressure 351
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
6.16.1 General remarks
The pressure module P8 contains 8 pressure sensors built into attachment nipples. Using an appropriate
coupling, tubes carrying gases or fluids whose pressure is to be measured can be connected at the
nipples. In the module's interior is an additional pressure sensor which serves as a barometer and
constantly measures the ambient air pressure.
6.16.2 Absolute and relative pressure
The 8 inputs have a fixed combination of sensors which depends on the model of the P8-module.
Absolute pressure sensors measure absolute pressure. A typical input range is 0..10bar. Absolute pressure
can never be less than 0bar, since 0bar is already a vacuum. If no medium is connected to a nipple with a
built-in absolute pressure sensor, then that sensor will measure the ambient air pressure. You would
then obtain measurement values around 1bar.
Relative pressure sensors measure pressure in relationship to the ambient air pressure. In this case, one
side of the sensor's membrane has contact to the medium to be measured, and to the surrounding air on
the other side. Depending on which side presses harder, the membrane is bent toward one side. Thus
relative pressure can be either positive or negative . Input ranges of ±300 mbar are typical. If nothing is
connected to the nipples, they deliver measurements of around 0mbar. The measurement value is
positive if the pressure of the medium is higher than the atmospheric pressure.
6.16.3 Barometer
The barometer inside the module can be used to obtain a measurement of relative pressure using the
absolute pressure sensor. The module itself refers to the built-in barometer and takes the difference. Use
the software to select the measurement type for each channel separately, which is equipped with an
absolute pressure sensor. A sensor with the input range 0...10 bar then can produce a relative pressure
input range of 1 bar..+9 bar, in other words, shifted down by 1 bar.
The built-in barometer requires permanent contact to the surrounding air. For this purpose, all housing
models come either with air-inlets or in the case of the IP65-housing, Goretex (R) membranes.