Calibration - Siemens 7MF4333 User Manual

Calibration and Maintenance

7.1 CALIBRATION

Calibration can involve adjusting zero to eliminate any position-induced zero shift, setting zero on-line,
and trimming the digital to analog converter. Transmitter calibration should be checked annually and a
calibration performed only if the transmitter is found to be out of tolerance. Trimming the D/A converter
should not be necessary and should be performed only after all other options have been exhausted.
Zero Shift Explanation
Zero shift can be predicted. Transmitters are calibrated at the factory in a vertical position (enclosure
directly over sensor). If a transmitter is installed (or will be installed) in another orientation, it may need
re-zeroing to eliminate position-induced zero shift, depending upon transmitter type and direction of
rotation. Maximum zero shift is 1.2 inches H
•
There is no zero shift with transmitter rotation as long as diaphragm orientation with respect to the
earth does not change.
For example, in the drawings below, rotating the transmitter from the vertical (center drawing) either
90° clockwise (right drawing) or counterclockwise (left drawing) will not cause a zero shift because
diaphragm orientation with respect to earth has not changed.
Diaphragm Plane for
these three orientations
•
Maximum zero shift occurs when rotating the transmitter causes diaphragm orientation with respect
to the earth to be changed 90°.
For example, in the drawings below, rotating the transmitter from the vertical (center drawing) either 90° clockwise
7-2
O (299 Pa).
2
+
(right drawing) or counterclockwise (left drawing) will cause
maximum zero shift because the diaphragm orientation
changes from vertical to horizontal.
Diaphragm Plane
+
Diaphragm Plane
Diaphragm Plane
UMSITRPSD3-1
MG00362a
MG00362a
November 2010