3. OPERATION
Page 29 © 2002-2007 DH Instruments, a Fluke Company
If the pressure unit selected is inWa (inches of water), the reference temperature for water
density must we specified in a separate menu (choices are 4 ºC, 20 ºC 60 ºF).
No reference temperature selection is necessary for the unit mmWa as the only reference
temperature commonly used for mmWa is 4 ºC.
The default pressure units of measure available under the UNIT function depend on whether
the PPC3 has been set up as an SI or US version (indicated by SI or US at bottom right of
introduction screen). The choice of six units available under the UNIT function can be
customized from a wider selection by the user (see Section 3.5.6). The units available under
the UNIT function can be reset to default by reset (see Section 3.5.4.2).
3.3.3 [MODE]
PURPOSE
To set the measurement mode (absolute, gauge or negative gauge) for the active range.
For information on selecting the unit of measure, see Section 3.3.2.
PRINCIPLE
PPC3 supports simple, one-step switching between up to three different measurement modes:
Absolute Measures pressure relative to vacuum (zero is hard vacuum). Range is
from zero absolute to full scale.
Gauge Measures pressure relative to atmosphere (zero is ambient pressure).
Range is from zero gauge to full scale, full scale must be greater than zero.
Negative gauge Measures pressure relative to atmosphere (zero is ambient pressure).
Range is negative and positive from zero, negative to minus one
atmosphere and positive to full scale. With a BGxxx RPT, negative range
is the negative equivalent of the positive range.
Which measurement modes are available depends on the type(s) of Q-RPT available. There are
three Q-RPT types:
Axxx Q-RPTs with designators starting with “A” measure pressure relative to a sealed
vacuum reference and are intrinsically absolute. Axxx Q-RPTs support
measurement in absolute, gauge and negative gauge modes. Gauge and negative
gauge modes are accomplished by PPC3’s automated offsetting of atmospheric
pressure and dynamic compensation for atmospheric pressure changes between
offsets using an on-board barometer (see Section 3.2.3). Access to absolute and
negative gauge operation can be turned OFF if these modes are not used (see
Section 5.2.5).
Gxxx Q-RPTs with designators starting with “G” measure positive pressure relative to the
TEST(-) port that is connected to atmosphere. Gxxx Q-RPTs support
measurement in gauge mode only.
BGxxx Q-RPTs with designators starting with “BG” measure positive and negative
pressure relative to the TEST(-) port that is connected to atmosphere. BGxxx
Q-RPTs support measurement in gauge and negative gauge modes.
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