Meriam M2 – Series Smart Manometer - Manual (Page 24)

18
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
4 times more accurate than the unit under test.
The re-calibration is not intended to replace the Factory Lab
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. For sensors 200 PSI and above, a
±0.0030% of reading deadweight tester is recommended. If
calibrating using inches of water units, be sure to match the
reference temperature of water in both the unit under test and the
M2. Note that AI type M200 manometers require Absolute
referenced dead weight testers or standards for field recalibration.
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.
For example: for a 2000 inH2O sensor, Point # 2 (25%) can be
edited from 495 to 505 inH2O. Point #5 (100%) can be edited
from 1980 to 2000 inH2O.
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 ty
pe, the user must first “Restore Factory Defaults” and
then choose the desired re-calibration method.