8270A/8370A
Operators Manual
40
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
uncertainty 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. Only modules that were
pressurized during the upward excursion are used during the downward
excursion. When controlling down in pressure, no module will be selected that
was not also used on the upward excursion.
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.
Pressure Filter
The pressure filter allows user adjustment from 1 to 99 values in a rolling
average. Set the value to 15 as default.
AutoZero
Pressure measurement devices naturally drift with time. This drift appears as an
offset. 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 automatically performed when the system
is vented and the pressure is stable, regardless of Autozero settings. 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 zero gauge
pressure.
Absolute Mode
For all absolute modules except PM500 models with range 700 kPa (100 psi)
absolute and lower, the zero correction mode is user-selectable in the Autozero
menu (
Setup Menu > Measure Setup > Autozero
). If unsure about Autozero in
absolute mode, leave the Autozero setting set to
Manual Entry
and do not use
the
Zero
button on the display.
Autozero in absolute mode can be done automatically or manually when the
system is vented and the pressure is stable. If a system has multiple absolute
mode absolute modules, then a module can be selected to measure the vented
barometric pressure and serve as the Autozero reference pressure source. This
is always the module with the lowest uncertainty at atmospheric pressure
(normally the lowest range absolute module). Select the slot number of this
module in the Autozero menu. When the zero correction is performed, all other
absolute mode modules will be corrected so their output equals the reading of
the selected reference module. Each modules' Autozero value is shown on its
calibration information screen as zOffset value.
