DH Instruments PPCK PLUS, Operation And Maintenance Manual

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PPCK+™ Operation and Maintenance Manual
Page 119
©2001 DH Instruments, Inc .
5.2.2 EQUIPMENT REQUIRED
The following specific items, in addition to a normally equipped pressure calibration
laboratory, are required to calibrate a PPCK+:
1. Gas operated piston gauge (deadweight tester) , with the following characteristics:
•
Measurement uncertainty of ± 0.005 % of reading or better , if best PPCK+
measurement uncertainty is to be obtained. A standard with higher measurement
uncertainty may be used but PPCK+ measurement uncertainty will be degraded
proportionally from published specifications.
•
Able to apply absolute pressures if the RPT will be used in the absolute
measure mode:
Absolute pressures in the range of PPCK+ are usually defined by
applying gauge (relative) pressures with a piston gauge and adding atmospheric
pressure measured by a precision barometer. If the PPCK+ RPT will
not be used in
absolute measure mode (as is often the case for high pressure RPTs), absolute
pressures are not required for calibration and the calibration may be performed by
applying gauge pressures only.
The measurement uncertainty in absolute measurement mode is unknown when a
PPCK+ RPT is calibrated in gauge mode. A PPCK+ calibrated in gauge mode should
not be used to make accurate measurement in absolute mode.
•
Able to apply pressures at 20 % increments in the range to be calibrated: It is
not necessary that the calibration pressure standard used apply precisely the
nominal pressure value requested for a calibration point as long as the exact value
of the applied pressure is known. Best results will be obtained if the pressure
actually applied is within ± 2 % of FS of the range being calibrated from the
nominal increment. For the zero point on absolute ranges, use the lowest point the
piston gauge can define accurately or atmospheric pressure if a barometer with
appropriate measurement uncertainty is available.
Contact DHI for additional information on calibration standards available to
calibrate PPCK+.
2. Precision barometer: Needed only if the PPCK+ RPT is to be calibrated in absolute
mode for absolute operation. The barometer is used to obtain absolute pressure by
adding atmospheric pressure to gauge pressure defined by a piston gauge. It is also
used to set ZNATERR to allow the use of the autozero function between calibrations (see
Section 3.4.1). Barometer measurement uncertainty should be
±
350 Pa (0.05 psi)
or better.
A recommended source for measuring atmospheric pressure to set ZNATERR and for
subsequent autozeroing is a DHI RPM3 reference pressure monitor. Contact DHI for
additional information.