Meriam M203 Altimeter Indicated Air Speed Tester - Manual (Page 23)

20
Re-Calibration
The Manometer can be re-calibrated in the field for zero, span, and linearity. The
proper primary standards must be available prior to calibrating the
Manometer. These standards should meet the accuracy requirements for your
company or industry. Meriam Process Technologies follows the guidelines
established by ANSI / NCSL Z540- 1-1994 which requires that the primary
standard be four times more accurate than the unit under test.
The re-calibration is not intended to replace the Factory Laboratory Calibration
Procedure. It is intended to correct the curve fit if the actual sensor
characteristics change slightly over time.
For sensors up to 200 PSI, Meriam recommends a ±0.0015% of reading
deadweight tester. If calibrating using inches or millimeters of mercury, be sure
to match the reference temperature of mercury in both the M203 and the
deadweight tester. The reference temperature for these units in the M203 is
0º C.
1-point (within upper 50% of Full Scale), 5-point (nominal values of 0%,
25%, 50%, 75% & 100% of Full Scale), and restore factory default re- calibration
options are offered. For the 5-Point re-calibration, points 2, 3 and 4 can be
adjusted within 1% of reading around the nominal values. Point #5 can be
adjusted within -1% of reading around nominal. Point #1 is fixed at zero.
For example: for a 900 mm Hg Abs sensor (nominal 17 PSIA), Point # 2
(25%) can be edited form 216 to 234 mm Hg Abs. Point #5 (100%) can be
edited from 891 to 900 mm Hg Abs.
The unit can only be re-calibrated if the calibration points are within 5 times the
accuracy of the original factory calibration (e.g., @ 0.05% accuracy, the point
limit is 0.25% of Full Scale). If the re-calibration procedure generates a new
value outside this limit the procedure will fail. In this case the unit would need to
be returned to the factory for service.
Once a re-calibration has been performed (either 1-point or 5- point) the unit will
continue to allow future re-calibrations only with that type of re-calibration. In
order to enable the other re- calibration type, the user must first restore the re-
calibration data to the factory defaults.