DH Instruments PPC3 - Pa and Pm Coefficients; As Received and as Left Data

PPC3™ OPERATION AND MAINTENANCE MANUAL
© 2002-2007 DH Instruments, a Fluke Company Page 122
When running calibrations, collecting as received data and calculating PA and PM
adjustments, whether AutoZ is normally used, whether it is ON or OFF and what the value of
Zoffset is should be considered (see Section 3.5.1,  PRINCIPLE).
CalTool for RPTs software provided with the PPC3 supports the calibration process of
PPC3 Q-RPTs. CalTool and its documentation are provided on a General Accessories Disk
with the new PPC3. Most users should use CalTool software to assist in the calibration of
PPC3.
PPC3 is delivered with an interactive Q-RPT calibration utility 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 (see the CalTool for RPTs
manual on the General Accessories Disk). PPC3 also provides complete front panel and
remote access to Q-RPT calibration parameters so that Q-RPT calibrations can be performed
without using CalTool software (see Section 5.2.8).
PPC3 may also use external Q-RPTs mounted in RPM4 Reference Pressure Monitors. RPM4 Q-RPTs
are calibrated independently of PPC3 (see the RPM4 Operation and Maintenance Manual).
5.2.1.1 PA AND PM COEFFICIENTS
The coefficients used to adjust Q-RPT readings are designated PA (an adder or
offset) and PM (a multiplier or span set). The coefficients affect the Q-RPT
reading following:
Corrected reading = (uncorrected reading • PM) + PA
PA is expressed in units of pressure (always the SI unit, Pascal).
PM is dimensionless.
Each Q-RPT has its own unique PA and PM values. The PA and PM values
currently in use can be viewed and edited in the CAL function (see Section
5.2.7). PA and PM values are automatically edited when CalTool software is
used and the results are activated.
As editing PA and PM values will change Q-RPT calibration, they should only
be edited by qualified personnel as part of the calibration process. Caution
should be taken to avoid accidental editing and a security system is
available to prevent access (see Section 3.5.5.5). Incorrect editing of PA
and PM values can cause out of tolerance measurements.
A new PPC3 is delivered with PA and PM values set to zero and 1 for all
ranges. This does not mean that the PPC3 has not been calibrated. In the original
factory calibration, privileged factory coefficients are used for calibration
with the user PA and PM set to zero and 1.
5.2.1.2 AS RECEIVED AND AS LEFT DATA
Frequently, calibration procedures require that as received and as left data be
reported. The necessary information to report as received and as left data on the
calibration of PPC3 Q-RPTs can be obtained in several ways.