DH Instruments E-DWT-H, Руководство по эксплуатации и обслуживанию

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E-DWT-H OPERATION AND MAINTENANCE MANUAL
© 2009 DH Instruments, a Fluke Company Page 98
5.2.2 Adjustment of the On-Board Barometer
 PURPOSE
To adjust the output of the on-board barometer (see Section 3.9.7.1).

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).
Note
The on-board barometer is used only for measuring changes in
atmospheric pressure over short periods of time (see Section 3.9.1).
RPM4-E-DWT measurement uncertainty 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-E-DWT’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.
Note
•
To view the current output of the on-board barometer, press
[SPECIAL], <7intern>, <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-E-DWT rear panel
Q-RPT modules (10-32 UNF). The operating span of the barometer is
10 psi (70 kPa) to 16 psi (110 kPa).
•
Never apply a pressure greater than 110 kPa (16 psi) to the barometer
port. Overpressure and possible damage may result.
5.3 RPM4-E-DWT Q-RPT Calibration
5.3.1 Principle
RPM4-E-DWT has one or two quartz reference pressure transducers (Q-RPTs) that are the
source of low pressure measurement uncertainty for the system.
To adjust a Q-RPT, pressures from a reference standard are applied to the Q-RPT at
ascending and descending pressure increments over the range. The pressure defined by the
standard and the corresponding Q-RPT readings are recorded at each point. After all of the
pressures have been applied and recorded, adjustments are made to fit the Q-RPT pressure
readings to the standard. Fitting the readings means performing a least squares linear
regression to arrive at the lowest value of the residuals of errors of the Q-RPT relative to the
standard. The Q-RPT output is adjusted by user settable coefficients: PA (an adder or offset)
and PM (a multiplier or span set) (see Section 5.3.1.1).
The calibration process is performed independently on each Q-RPT to arrive at its optimal fit.
RPM4-E-DWT is delivered with an interactive Q-RPT calibration utility (CalTool for RPTs) that
steps the operator through the complete Q-RPT calibration procedure including applying the
necessary pressures, collecting data automatically, calculating new PA and PM values,
previewing the results of the new calibration and activating the results of the new calibration.