Fluke RPM4-AD, Руководство по эксплуатации и обслуживанию

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3. OPERATION
Page 59 © 2005-2007 DH Instruments, a Fluke Company
When gauge or negative gauge mode is first activated, the value of P
offset.G
subtracted
from the absolute pressure reading to achieve gauge pressure is standard atmosphere of
101.325 kPa. This can cause a large zero error when gauge mode is activated if
atmospheric pressure is significantly different from standard atmospheric pressure.
When gauge mode is activated, always press [AutoZ] to run AutoZ and obtain an actual
value of
P
offset.G
.
AutoZ in differential measurement mode
RPM4-AD supports differential measurement mode (see Section 3.2.6) in which the
measured pressure is the difference between the pressure measured by the Hi Q-RPT (Pt)
and the Lo Q-RPT (Ps) (Hi – Lo, Pt – Ps).
In differential measurement mode, the purpose of AutoZ is to compensate for the offset
between the Hi and Lo Q-RPT indications at the “line pressure” at which the differential
pressure is being measured. In differential measurement mode, when the active unit of
measure is an airspeed unit, the line pressure is altitude. The value of
P
std,0
is the pressure
measured by the Lo Q-RPT at the time of AutoZ.
In differential measurement mode, with AutoZ ON, differential pressure is calculated as:
P
differential
= P
Hi
- P
Lo
- P
offset,D
In differential measurement mode, AutoZ is run when initiated by the operator pressing
[AutoZ] . RPM4-AD’s differential mode AutoZ function connects both RPTs together
internally to the TEST (Ps) port to be sure they are exposed to the same pressure.
AutoZ ON/OFF
The AutoZ function can be turned ON and OFF, separately for gauge, absolute and
differential measurement modes and for each Q-RPT. Table 11 summarizes the effect of
AutoZ ON and OFF.
Table 11. AutoZ ON and OFF
MEASUREMENT
MODE
AutoZ
STATUS
P
offset
APPLIED
Δ P
atm
APPLIED
AutoZ
ROUTINE
RUNS
ON YES
When initiated
by operator
Absolute
OFF NO
Not Applicable
Not available
ON YES
Gauge or
negative gauge
OFF
YES
NO
When initiated
by operator
ON YES
When initiated
by operator
Differential
OFF NO
Not Applicable
Not available
Recommendations for the Use of the AutoZ Function
The AutoZ function provides a powerful and easy to use tool for improving the stability over
time of RPM4-AD Q-RPTs and maximizing the recalibration interval by compensating for zero
drift between full recalibrations. In differential measurement mode, it minimizes the
uncertainty in the differential pressure due to the offset between the Hi and Lo Q-RPTs at the
“line pressure” (altitude in air data measurement). The following simple recommendations
will help assure that you use the AutoZ feature to best advantage.
•
In gauge and differential measurement mode: Always leave AutoZ ON when operating.
•
In absolute measurement mode: Always leave AutoZ ON when operating if the AutoZ
routine has been run regularly using a valid atmospheric reference.