PPC2 AF OPERATION AND MAINTENANCE MANUAL
© 1998 DH Instruments, Inc. Page 108
The PA/PM values used by the on-board calibration function and accessible under SPECIAL,
4Internal, 2Cal are the user PA/PM values. These values are set at the factory on a new
PPC2 AF to have no effect (PA = 0, PM = 1). Thus, their change over time can be used as a
measure of the evolution over time of the reference pressure transducer calibration. PA/PM
values are also available under SPECIAL, 4Internal, 5Diag, 2Calib. These are the factory
PA/PM values and should not be changed by the user.
As editing PA/PM values will change the calibration of the reference pressure transducers,
they should only be edited by qualified personnel as part of the calibration process. Care
should be taken to avoid accidental editing (see Section 2.4.2). For recalibration, only the
user PA/PM in SPECIAL, 4Internal, 2Cal menu should be used. The factory PA/PM in
SPECIAL, 4Internal, 5Diag, 2Calib should not be altered.
Setting PA(z)tare
Setting PA(z)tare is necessary for the AutoZ function that "rezeros" the reference transducers
between calibrations to function properly (see Section 5.2).
Setting PA(z)tare is procedurally identical to running the AutoZ function but the result is
changes to the PA(z)tare value rather than the PA(z)net value. The PA(z)tare setting
procedure occurs automatically as part of the on-board reference pressure transducer
calibration procedure. It can also be run separately under SPECIAL, 4Internal, 2Cal.
As the PA(z)tare must reflect the "natural" error between the reference transducer
reading and the zero reference pressure at the time the reference transducer is
calibrated, the PA(z)tare function should not be executed between calibrations. Only the
AutoZ function should be used to "rezero" the reference transducer between calibrations
(see Section 5.2).
Order of Operations
Given certain interdependence of reference pressure transducer measurements it is
important that the calibration and determination of PA(z)tare be performed in a certain order
as follows:
1. Calibrate the range or ranges to be calibrated on the Lo reference transducer.
2. Determine PA(z)tare of the Lo reference transducer.
3. Calibrate the range or ranges to be calibrated on the Hi reference transducer.
4. Determine PA(z)tare of the Hi reference transducer.
This order is required because a) the PA(z)tare value of a reference transducer must reflect
the "natural" error of the transducer after the transducer has been calibrated (see Section 5.2)
and b) the PA(z)tare of the Hi reference transducer is determined relative to the Lo reference
transducer.
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