Pressure Controller/Calibrator
Pressure Measurement Settings
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Module Selection
The Product selects the active pressure measurement module in these different
ways:
Auto – This is the default setting. The Product selects the module with the lowest
pressure range that is sufficient to measure the current pressure.
Fast – The Product selects the module with the lowest pressure range that is
sufficient to measure the Setpoint. With this method, the Product does not switch
ranges during an upward pressure application but instead switches immediately
to the required range and stays on that range.
Fixed – The Product always keeps the user-selected range active. With this
selection, a setpoint outside the measuring range of the selected module cannot
be entered.
AutoZero
Pressure measurement devices naturally drift with time. This drift appears as an
offset at zero pressure. To ensure the accuracy of the measurement, it is
important to correct for this drift whenever possible.
Gauge Mode
The zero correction in gauge mode is performed when the system is vented and
the pressure is stable. At that time, the internal valves are configured such that
the test port and reference port see the same pressure and that pressure is open
to atmosphere through the vent port. Zero gauge pressure is defined as
atmospheric pressure. In this condition, the pressure measurement modules, by
definition, measure the zero gauge pressure. When the system is vented and
stable, zero correction is automatic, regardless of the setting for AutoZero.
Absolute Mode
Zero correction in absolute mode is also automatic when the system is vented
and the pressure is stable. However, this correction is more challenging. To zero
an absolute sensor, the barometric pressure must be known. If a system has
multiple absolute mode absolute modules, then a module can be selected to
measure the vented, barometric pressure. This should always be the range with
the lowest uncertainty at atmospheric pressure (normally the lowest range
absolute module). When the zero correction is performed, all other absolute
mode modules will be corrected such that their output equals the reading of the
selected module. If a sufficiently accurate module is not included in the system,
select the manual zeroing mode. In this mode, push the zero button on the main
display to initiate the zeroing routine when the system is vented and stable. Enter
the current barometric pressure as determined through an external reference
such as a barometer or piston gauge.
If a module is selected as the AutoZero reference, but is then removed from the
system, the system reverts to manual zeroing mode. The system returns to
AutoZero mode when the selected module is returned to the system or when you
select a different module.
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