P8 pressure 353
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
6.16.5 Factors affecting pressure measurement
Precise pressure measurement requires observance of and compliance with certain constraints.
1. Position-dependence: The measured value returned depends on how the sensor is positioned
when in use. For this reason, observe the "preferred mounting position". This is the position in
which the sensors are calibrated at the factory. The sensors' high sensitivity can lead to offset
errors when the position is changed, due to the effect of gravity upon the sensor's own oil column.
It is important to compensate for this offset, especially for measurements of relative pressure
around zero. This can be accomplished using the operating software.
2. Frequency response: The sensors' natural frequency is higher than the maximum measurable
frequency of 500 Hz. However, the frequency response of the signal connected to the CAN-bus is
not only determined by the sensor's frequency response but also by the anti-aliasing filter in the
pressure module's electrical portion.
3. Motion: If the module is moved, the forces acting on it (e.g. inertia operating on the medium to
measure or the membrane itself) can cause measurement distortion. Not that the pressure module
responds sensitively to pressure on the membrane, but that these forces can be caused by pressure
in the medium.
4. Drift: Highly sensitive pressure sensors come with a certain amount of drift. This means that the
error in the measurement value is not constant, but time-dependent. Of course, the error remains
below the limit stated in the spec sheet. The drift usually takes the form of a creeping change in the
offset. Therefore, in measurements of relative pressure, the offset should be tared to zero every
once in a while. This can be done with the help of the operating software.
5. Air bubbles: Pockets of air must be avoided, especially with fluid media.
6. Elevation differences: If there is a difference in elevation between the sensor and the
measurement site, the pressure differential affects the measurement. This must be taken account
of, especially with fluids, and can be compensated by subtraction.
7. Leaks: Only the precise coupling mechanisms specified for the particular medium may be used or
else you risk leakage.
8. Low-pass: When connecting the medium, the low-pass behavior of long tubes must be considered.
To measure rapid pressure change, keep the tubing as short as possible.
You risk permanent damage by pulling the tube off self-closing nipples under high pressure. The
pressure remains intact at the sensor. If the temperature rises subsequently, the sensor could be
permanently damaged. Therefore, always ensure ventilation.
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