Related Information
110 MC4 User Guide
Things to Consider when Measuring Pressure
General
MC4 can measure pressure with its internal pressure module or with
external pressure modules. If a barometric module is present, the
measurement results of other modules can be shown either as
absolute pressure or as gauge pressure.
Pressure Type
Every pressure measurement is in fact a pressure difference
measurement: a given pressure value is compared against a
reference pressure. In certain cases the reference pressure has a
special meaning (like the atmospheric pressure) and the pressure
measurements with reference to against these points are given a
special name:
• Absolute pressure measurement uses vacuum as the
reference pressure.
• Barometric pressure (or atmospheric pressure) is the
absolute pressure of the surrounding atmosphere. It is
specially titled because of its importance.
• Gauge pressure measurement uses the atmospheric
pressure as the reference. Gauge pressure may be zero,
negative or positive. Most of MC4's pressure modules actually
measure gauge pressure although they may be used for
measuring other pressure types too.
• Differential pressure measurement requires a special
differential pressure module that has an input available for
both the reference pressure and the given pressure.
To be able to measure absolute pressure with MC4's gauge
pressure modules, you need a barometric pressure module. Certain
high pressure modules may approximate absolute pressure
measurement by adding an entered barometric pressure to the
measured gauge pressure.
MC4 may use two standard pressure modules to measure (pseudo)
differential pressure: One module measures the reference pressure
and another the given pressure. The pressure difference is
calculated by subtracting the reference pressure from the given
pressure. More of this in Part B, chapter Display Mode and Special
Measurements.
Always ensure that the pressure type setting of your pressure
measurement is what you intended it to be. The pressure type
setting is crucial for getting meaningful pressure measurement
results.
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