E-DWT-10000-AF OPERATION AND MAINTENANCE MANUAL
© 2008 DH Instruments, a Fluke Company
Page 64
3.9.7.1
<1BARO>
PURPOSE
To view the value of atmospheric pressure as measured by the RPM4-E-DWT
on-board barometer.
PRINCIPLE
RPM4-E-DWT A70M/A7M-AF is equipped with an on-board barometer. The
atmospheric pressure measurements made by the on-board barometer are used
for dynamic compensation of atmospheric pressure when making gauge pressure
measurements (see Sections 3.9.1).
See Section 5.5.4 Figure 14 and Section 5.5.6, Figure 15 for a photo and
schematics showing the position of the on-board barometer in RPM4-E-DWT.
The on-board barometer is a low accuracy sensor used only for measuring
small changes in atmospheric pressure over short periods of time (see Section 3.9.1).
RPM4-E-DWT measurement uncertainty does not depend on the measurement
uncertainty of the on-board barometer.
OPERATION
To view the current reading of the on-board barometer press
[SPECIAL]
,
<7intern>
,
<1baro>
. The display is in the active pressure unit of measure
(see Section 3.7.3). The display resolution is fixed to 0.1 Pa, or its equivalent.
3.9.7.2
<2R
EAD
R
T
>
PURPOSE
To turn ON and OFF RPM4-E-DWT’s automated, rate of change dependent,
reading integration and display rate feature.
PRINCIPLE
To obtain maximum resolution from RPM4-E-DWT Q-RPT pressure
measurements, an integration time of about 1.2 second per reading is used. In
most situations, maximum precision is needed when pressures are stable so a
relatively slow display update rate presents no disadvantage. However, when
pressure is changing quickly, more rapid pressure updates are usually more
important than obtaining maximum precision on individual readings. The
RPM4-E-DWT read rate function automatically adjusts pressure measurement
integration time depending on the rate of change of pressure. When pressure is
changing rapidly, reading rate is increased. When pressure is evolving slowly,
reading rate is decreased and maximum precision is obtained.
When the automated read rate function is ON, three pressure rate of change
dependent read rates are used. The result is three display update rates:
Table 7.
READRT – display update rates
PRESSURE
RATE OF CHANGE
DISPLAY
UPDATE
> 3 % of range span/s
≈
0.2 s
> 0.5 and < 3 % of range span/s
≈
0.6 s
< 0.5 % of range span/s
≈
1.2 s
