Meriam M1 – Series Digital Manometer - Manual (Page 10)

M1 Series - DM Instruction Manual 9R000034-IR
E.O. 6409 JAN 2008
www.meriam.com
Page 10 of 17
Field Recalibration
The M1 can be recalibrated in the field for zero and span. The
proper primary standards must be available prior to calibrating the
unit. These standards should meet the accuracy requirements for
your company or industry. Meriam Process Technologies follows
the guidelines established by ANSI/NCSL Z540 which requires
that the primary standard be 4 times more accurate than the unit
under test.
The field recalibration is not intended to replace the Factory
calibration procedure. It is intended to trim the factory calibration
curve fit to accommodate slight changes in sensor characteristics
over time.
ZERO
To Zero the M1, first turn off pressure sources and vent pressure
ports to atmosphere. Then simultaneously press and hold the F
and U keys until “F.CAL” is displayed. The process is complete
when the display changes from “----” to a “zero” reading.
Note: The M1 can only be zeroed if the measured zero is within
±2.5% (of FS) of the factory calibrated zero.
At this point, the M1 can be zeroed.
The above process applies only to gauge and differential
pressure instruments. To recalibrate the zero on an absolute
pressure instrument, the applied pressure must be within 10
times the full scale accuracy term of the original factory
calibrated zero. 200 microns is Meriam’s standard vacuum
reference for all absolute pressure sensors.
Note: It should be noted that if the zero reference source used to
recalibrate any pressure instrument is not accurate, the M1
zero can be recalibrated to a maximum discrepancy of
2.5% of the original factory zero. This can create a 2.5%
offset in all pressure measurements after the recalibration
of zero.
If this procedure generates a new value outside this limit,
the red backlight will flash to indicate the procedure failed
and the previous value was retained.