DH Instruments ADCS-601, Operation And Maintenance Manual

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7. MAINTENANCE OF TRACEABILITY AND RECALIBRATION
Page 135 © 2005 DH Instruments, Inc.
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M
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A
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7.1 PRINCIPLES OF ADCS-601 TRACEABILITY MAINTENANCE
The ADCS-601 system is designed to provide state of the art measurement uncertainty specifications
with a very high degree of confidence over time whle minimizing maintenance requirements.
The maintenance of traceability and associated recalibration of the ADCS-601 system requires
metrological maintenance procedures that are performed locally at regular intervals (see Section 7.2) and
the regular recalibration of certain system elements (see Section 7.3).
ADCS-601 is made up of two pressure standards, a PG7601 piston gauge for the majority of the range
and an FPG8601 force balanced piston gauge for the low end. The fact that ADCS-601 includes two
independent pressure standards is exploited to reduce recalibration requirements. The two standards
have ranges that overlap between 10 and 15 kPa (3 and 4.5 inHg).
The PG7601 measurement uncertainty is predominantly dependent upon the uncertainty in the effective
area of its piston-cylinder and the value of the masses that are loaded on the piston-cylinder (see Section
2.2.1). The FPG8601 measurement uncertainty is predominantly dependent upon the effective area of its
piston-cylinder, the value of its internal calibration mass and the linearity and repeatability of its force
balanced load cell (see Section 2.2.2).
In the air data range of 1 to 15 kPa (0.3 to 4.5 inHg) that is covered by the FPG8601 in the ADCS-601
system, the typical pressure measurement uncertainty of the FPG8601 (see the most recent revision of
DHI Technical Note 2090TN05) is much lower than is required to maintain an adequate uncertainty ratio
with modern Air Data Test Sets (ADTS). For use in the ADCS-601 system, the FPG8601 measurement
uncertainty specification is significantly expanded from its typical measurement uncertainty to allow it to
be validated within the ADCS-601 system and its calibration interval to be indefinite. When the internal
ADCS-601 validation procedures determine a possible out of tolerance condition of the FPG8601 it is
considered to have failed and to require repair.
7.2 LOCAL METROLOGY MAINTENANCE BETWEEN
RECALIBRATIONS
7.2.1 OVERVIEW
To assure that the ADCS-601 operates within pressure measurement uncertainty limits between
recalibrations, certain metrology maintenance functions are required. These are summarized in
Table 21, including cross-reference to manual sections detailing each procedure.