DH Instruments PPC2+, Руководство пользователя

Страница: 134 / 166

PPC2+™ Operation and Maintenance Manual
©2001 DH Instruments, Inc.
Page 126
5 . 2 C A L I B R A T I O N O F R E F E R E N C E P R E S S U R E
T R A N S D U C E R S
5.2.1 PRINCIPLE
PPC2+ has one or two reference pressure transducers (RPT) that are the source of accurate
pressure measurement for the system. Each transducer has three independent ranges.
To calibrate a range, pressures from a standard are applied to the RPT at ascending and
descending points over the range. The pressure defined by the standard and the
corresponding RPT readings are recorded at each point. After all of the pressures have been
applied and recorded, adjustments are made to fit the 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 transducer relative to the standard. The transducer readings are
adjusted by user settable coefficients: PA (an adder or offset) and PM (a multiplier or span
set) (see Section 5.2.1.1).
The calibration process is performed independently on each range of each RPT to arrive at
the optimal fit for each range. This technique allows improved accuracy for individual ranges
lower than the RPT’s maximum range by taking into account specific transducer performance
characteristics, in particular localized non-linearity and excursion dependent hysteresis.
Independent range calibration also makes it possible to calibrate only certain ranges if ranges
are on different calibration intervals or not all ranges are needed.
The normal calibration process for absolute RPTs has a second step which is the
determination of the value of ZNATERR (see Section 5.2.1.2). This added step is necessary
to get the full benefit of the autozero function between calibrations (see Section 3.4.1). It is
only needed if the RPT will be operated in absolute measure mode.
-KV>YYV PY\ <:>] ]YP^aK\O Z\Y`SNON aS^R ^RO ::- ]_ZZY\^] ^RO MKVSL\K^SYX Z\YMO]] YP
::-<:>]-KV>YYVKXNS^]NYM_WOX^K^SYXK\OZ\Y`SNONYXK1OXO\KV+MMO]]Y\SO].S]UaS^R
^ROXOa::-7Y]^_]O\]]RY_VN_]O-KV>YYV]YP^aK\O^YK]]S]^SX^ROMKVSL\K^SYXYP::-
PPC2+ is delivered with an interactive RPT calibration utility that steps the operator through
the complete reference transducer calibration procedure including applying the necessary
pressures to each range, collecting data automatically, calculating new PA/PM values,
previewing the results of the new calibration, determining ZNATERR and activating the results
of the new calibration (see the CalTool for RPTs manual on the General Accessories Disk).
PPC2+ also provides complete front panel and remote access to RPT calibration parameters
so that RPT calibrations can be performed without using CalTool software (see Section 5.2.7).
=OO ^RO ::- ,1 9ZO\K^SYX KXN 7KSX^OXKXMO 7KX_KV PY\ SXPY\WK^SYX ]ZOMSPSM ^Y
MKVSL\K^SYXYP^RO,1<:>