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2271A
Operators Manual
44
Module Selection
The Product selects the active pressure measurement module in these different
ways:
Fixed – The Product always keeps the user-selected range active. The display
shows the modules in slot 1 and 2. Choose either of these or use the other
modes. The Product does not accept a setpoint outside the measuring range of
the selected module.
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.
AutoZero
In normal use, the barometer module (if installed) reads atmospheric pressure
through the REF port on the top of the Product. This limited use and the intrinsic
measurement characteristics of the barometer module offer a stable reference
pressure for measurement assurance features. A direct reading of atmospheric
pressure also lets the Product determine gauge pressure with the intrinsically
absolute pressure module and to measure absolute pressure with the gauge
pressure modules. The AutoZero feature compares the active pressure module
output to the internal atmospheric pressure reference, tares the difference, and in
some modes, dynamically compensates for changes in atmospheric pressure.
The function happens automatically during each vent operation after the Product
has determined that a pressure measurement is fully vented and stable.
Depending on what type of PMM is installed and which measurement mode is
selected, AutoZero tares as follows:
• For PMMs that are intrinsically gauge being used for gauge measurements
(for example, PM200-G400K in Gauge mode), AutoZero tares the reading to
zero gauge pressure at vent.
• For PMMs that are intrinsically gauge being used to make simulated absolute
pressure measurements (for example, PM200-G7M in ABS mode), AutoZero
tares the reading to zero gauge pressure measurement at vent. For
subsequent measurements, the Product dynamically compensates the output
to show absolute pressure by adding the outputs of the active gauge
pressure module and the barometer module.
• For PMMs that are intrinsically absolute being used for gauge measurements
(for example, PM200-A200K in Gauge mode), AutoZero tares the reading to
zero gauge pressure at vent.
• For PMMs that are intrinsically absolute and used for absolute measurements
(for example, PM200-A200K), Auto Zero tares the module's reading so that it
equals the reading from the most accurate absolute module installed. PM200-
AXXX modules do not have internal barometers.
Note
An AutoZero is performed prior to running HART tasks when in
gauge mode.
1.888.610.7664 sales@GlobalTestSupply.com
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