Fluke Calibration RPM4, Руководство по эксплуатации и обслуживанию

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3. OPERATION
Page 19
In differential measurement mode (see Section 3.3.3.1), the LED Ready/Not Ready
indication applies to the differential pressures.
In parallel measurement mode (see Section 3.2.4), the LED Ready/Not Ready indication
applies to the average pressure read by the <HL> Q-RPT.
When RPM4 is being used as an external measurement reference of a PPC3 pressure
controller, the Ready/Not Ready indication is still based on the RPM4 stability and
stability limit only. The RPM4’s Ready/Not Ready LED does not indicate whether the
PPC3 pressure control is Ready.
3.2.2 GAUGE AND NEGATIVE GAUGE MODES WITH AN AXXX
(ABSOLUTE) Q-RPT, DYNAMIC COMPENSATION FOR
ATMOSPHERIC PRESSURE
Q-RPTs with the designation Axxx are intrinsically absolute but they are also used for gauge and
negative gauge measurement modes (see Section 3.3.3,
 PRINCIPLE). Gauge measurement
modes are achieved by subtracting the value of atmospheric pressure, P
offset,G
, from the
Q-RPT’s absolute reading using AutoZ (see Section 3.2.2). The AutoZ routine that measures
P
offset,G
, is run by pressing [AutoZ] whenever RPM4 is in the vented condition. This assures
the continuous updating of the P
offset,G
value corresponding to atmospheric pressure. Gauge
pressure is the measured absolute pressure, P
u
, minus the atmospheric offset.
P
gauge
= P
u
- P
offset,G
However, atmospheric pressure may change between opportunities to run AutoZ and update
the value of
P
offset,G
, for example when running an extended test without venting. RPM4 uses
dynamic compensation for atmospheric pressure to correct for changes in atmospheric
pressure between opportunities to run AutoZ and update P
offset,G
. When AutoZ runs, and
P
offset,G
is determined, the reading of RPM4’s on board barometer, P
atm,0
, is also recorded.
Later, when no longer vented, the change in atmospheric pressure, ∆ P
atm
, since P
offset,G
was
updated, is the difference between the current barometer reading, P
atm
, and the barometer
reading at the time of AutoZ execution, P
atm,0
:
∆ P
atm
= P
atm
- P
atm,0
Dynamic compensation for atmospheric pressure uses ∆ P
atm
to correct the value of P
offset,G
,
thus always compensating real time for changes in atmospheric pressure:
P
gauge
= P
u
- P
offset,G
- ∆ P
atm
Gauge pressure measurement on an Axxx (absolute) Q-RPT allows instantaneous switching
between gauge and absolute measurements modes. The additional uncertainty in gauge
pressure mode due to the dynamic compensation for atmospheric pressure technique is a
function of the resolution and short term stability of the on-board barometer, not its absolute
measurement uncertainty. This additional uncertainty is ± 1 Pa (0.00015 psi).
3.2.3 MULTIPE RANGES (Q-RPTS, AUTORANGE AND INFINITE
RANGING)
An RPM4 may have one or two Q-RPTs. Position indication of the currently active Q-RPT is
continuously displayed in the upper right hand corner of the MAIN RUN screen and most other
screens. See Table 3 for position designation protocol for the Q-RPTs in an RPM4.
See Table 1 for a complete listing of RPM4/RPM4 Q-RPT choices and their default ranges.