DH Instruments PPCK PLUS, Operation And Maintenance Manual

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PPCK+™ Operation and Maintenance Manual
Page 117
©2001 DH Instruments, Inc .
5.2.1.1 PA AND PM COEFFICIENTS
The coefficients used to adjust RPT readings are designated PA (an adder or offset)
and PM (a multiplier or span set). The coefficients affect the RPT reading following:
Corrected reading = (uncorrected reading • PM) + PA
PA is expressed in units of pressure (always the SI unit, Pascal).
PM is dimensionless.
There are individual PA and PM values for each of PPCK+'s three ranges.
The values of PA and PM currently in use can be viewed using the CAL function (see
Section 5.2.5). PA and PM values are automatically edited when CalTool software is
used and the results are activated. PA and PM values can also be edited manually
under the CAL function (see Section 5.2.5).
As editing PA and PM values will change RPT calibration, these should only be edited
by qualified personnel as part of the calibration process. Caution should be taken to
avoid accidental editing (see Section 3.4.4.6).
A new PPCK+ is delivered with PA and PM values set to 0 and 1 for all ranges.
This does not mean that the PPCK+ has not been calibrated. For the original factory
calibration, PA and PM are set to 0 and 1 and privileged factory coefficients are used
for calibration adjustment.
5.2.1.2 SETTING ZNATERR
Setting ZNATERR is necessary on RPTs that will be used in the absolute
measurement
mode. It is only needed if the AutoZ function that rezeros the
reference transducers between calibrations is to function properly (see Section 3.4.1)
in absolute measurement mode.
Setting ZNATERR is procedurally identical to running the AutoZ function (see
Section 5.2.1.2), but the result is changes to the ZNATERR value rather than the
ZOFFSET value. The ZNATERR setting procedure is prompted automatically by
CalTool software. It can also be run separately by pressing
[SPECIAL] and
selecting <4Internal> , <2Cal> .
Since ZNATERR is a measurement of the “natural” disagreement between the
PPCK+ range in absolute measurement mode and a barometric reference, the
PPCK+ range must be calibrated and new PA and PM applied BEFORE ZNATERR
is determined.
As ZNATERR must reflect the "natural" error between the RPT and ZSTD at the time
the reference transducer is calibrated, the run ZNATERR function should not be
executed between calibrations. Only the AutoZ function should be used to "rezero"
the reference transducer between calibrations (see Section 3.4.1).