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RPM4/HPMS A70M/A20M-AF OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company Page 106
If the RPM4 is used only in gauge mode, Autozeroing in absolute mode is not
necessary and vice-versa. Gauge and absolute mode Autozeroing are
completely independent one from the other.
See Section 3.5.1 for complete information on Autozeroing of RPTs.
5.2.1.2 ABSOLUTE MODE AUTOZERO
When operated in absolute mode, a Q-RPT should be Autozeroed about once a
month or when the RPM4 has been exposed to a temperature change exceeding
15 ºC (36 ºF). Whether or not AutoZeroing is necessary can also be evaluated by
comparing the reading of the RPM4 Q-RPT to the reading of a barometer when
the RPM4 is vented at atmospheric pressure. The barometer should have
measurement uncertainty of 0.04 psi (0.28 kPa) or better. For the Lo Q-RPT, if
the disagreement is greater than 0.05 psi (0.35 kPa), the Q-RPT should be
rezeroed against the barometer. For the Hi Q-RPT, if the disagreement is
greater than 0.15 psi (1 kPa), it should be rezeroed against the Lo Q-RPT or
against the barometer.
Follow the procedures described in Section 3.3.9.2 to perform absolute mode
Autozeroing.
5.2.2 ADJUSTMENT OF THE ON-BOARD BAROMETER
PURPOSE
To adjust the output of the on-board barometer (see Section 3.5.7.1).
PRINCIPLE
The on-board barometer output can be adjusted using PA and PM values following the same
principles as for the Q-RPTs (see Section 5.3.1.1).
Since the on-board barometer is not a source of traceable pressure values, it does not have
to be formally calibrated. It should be offset to agree with a reference barometer. To offset
the barometer, change the barometer pressure adder (PA).
The on-board barometer is used only for measuring changes in atmospheric pressure over
short periods of time (see Section 3.2.3. RPM4 measurement accuracy does NOT depend on the
absolute accuracy of the on-board barometer.
OPERATION
To view or edit the values of PA and PM for RPM4’s on-board barometer, press [SPECIAL],
<8cal>, <3barometer>. Pressing [ENT] steps through displays of the calibration date
[YYYYMMDD] and PA and PM. In edit mode, the values can be edited. Pressing [ENT]
after the last screen activates the edited values.
To view the current output of the on-board barometer, press [SPECIAL], <7Internal>,
<3baro> from the main run screen.
A pressure standard may be connected to the on-board barometer by connecting to one of
the ATM ports on the RPM4 rear panel Q-RPT modules (10-32 UNF). The operating span of the
barometer is 10 psi (70 kPa) to 16 psi (110 kPa).