High-Pressure Modular Controller
Pressure Measurement Settings
41
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. For PM500 module zeroing see
PM500 Absolute
Zeroing
.
If a sufficiently accurate module is not included in the system, select the Manual
Entry zeroing mode in the Autozero menu. 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. The value must be between
75 kPa to 110 kPa (11 psi to 16 psi). Do not enter zero (0) for this value or your
pressure readings will be offset by about 100 kPa (14.6 psi) in absolute mode.
If unsure how Autozero works in absolute mode, it is best to leave the Autozero
setting set to Manual Entry and do not user the Zero button on the display.
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.
Atmosphere
Atmospheric pressure (ATM) is most often used to measure absolute pressure
with gauge mode modules. This is done by adding ATM to the current gauge
mode pressure reading. ATM is also used as the target pressure when venting in
absolute mode. From the Atmosphere menu (
Setup Menu>Measure
Setup>Atmosphere
), select the barometric reference module (PM200-A100K,
PM500-A120K, PM500-BA120K, PM500-A200K, or BRM600-BA100K) or
manually enter a barometric pressure value from an external lab barometer. A
barometer module must be installed to select a module for the atmospheric
pressure source. If
Manual Entry
is selected, enter a suitable uncertainty value
because in absolute mode (and also Auto or Fast mode, not Fixed mode) the
active module is selected by the lowest uncertainty of the module and the
atmospheric uncertainty value (if used). If the uncertainty value is unrealistically
low, the manually-entered value of atmospheric pressure may be used and
cause incorrect module selection.
Note
Any module selected for ATM cannot be then selected by the user or
the controller as the active module to directly measure absolute
pressure. If you need to use the selected ATM module to directly
measure absolute pressures, then do not select it as the ATM
source.
