Meriam M1 – Series Pressure Calibrator - Manual (Page 11)

M1 Series – PC Instruction Manual 9R000035-IR
E.O. 6409 JAN 2008
www.meriam.com
Page 11 of 18
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
Z540-1-1994 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 original factory
calibration. 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 applied pressure is within 1% of the
full scale range.
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 1.0% of the original factory
zero. This can create a 1.0% 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.