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5. MAINTENANCE, ADJUSTMENTS AND CALIBRATIONS
Page 115 © 2004-2007 DH Instruments, a Fluke Company
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5.1 OVERVIEW
RPM4 was designed for maintenance free operation. No maintenance is required other than:
• Regular AutoZeroing of quartz reference pressure transducer(s) (Q-RPT) (see Section 3.5.1).
• Periodic calibration of Q-RPT(s) (see Section 5.2).
• Adjustment of the on-board barometer, if present (see Sections 5.3).
This section provides information on maintenance, adjustment and calibration procedures, and recommended
overhaul procedures.
RPM4 is a sophisticated pressure measuring instrument with advanced on-board features and
functions. Before assuming that unexpected behavior is caused by a system defect or breakdown, use
this manual and other training facilities to become thoroughly familiar with RPM4 operation.
For rapid assistance in specific situations see Chapter 6 for troubleshooting information.
RPM4 is covered by a limited one (1) year warranty. Unauthorized service or repair during the warranty
period is undertaken at the owner’s risk and may cause damage that is not covered under warranty
and/or may void the warranty. For warranty service, contact a DHI Authorized Service Provide (see
Table 29).
5.2 CALIBRATION OF QUARTZ REFERENCE PRESSURE
TRANSDUCERS (Q-RPTS)
5.2.1 PRINCIPLE
RPM4 is equipped with one or two quartz reference pressure transducers (Q-RPTs)
used for low uncertainty pressure measurement.
To calibrate a Q-RPT, pressures from a reference standard are applied to the Q-RPT at
ascending and descending pressure increments over the range. The recommended
pressure sequence for a calibration varies depending on whether the Q-RPT is of Standard or
Premium class (see Section 1.2.2.1). 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 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 5.2.1.1).