How to Calibrate Offset Displacer Level Transmitter


*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
WARNING – If the process is hazardous, please unsure proper flushing is done to remove the entire hazard.
Remove isolation drain valve and open the vent flange
*Connect water pump to drain line and line up the reference tube
*Calculate the new measurement to get equivalent up trust force with S.G and length
*Mark on the chamber for reference calibration
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Apply water level until 0% marking on chamber
*Multimeter should show 4mA
*If not, do zero adjustment at transmitter using HART Communicator
Apply water level until 100% marking on chamber
Multimeter should show 20mA
*If not, do span adjustment at transmitter using HART Communicator
Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)

Example calculation:

Low S.G=0.802
High S.G= 0.992
A= 810mm (measurement length)
B= 410mm (off set)
C=A+B=1220mm (Displacer length)
0%    = (High S.G x off set length) + (low S.G x A)
= (0.992 x 410) + (0.802 x 810)
= 406.72 + 649.62
= 1056.34mm
100%     = (High S.G x C)
= (0.992 x 1220)
= 1210.24mm

Related post:

Calibration displacer type level transmitter
Calibration flow transmitter – DP type
Calibration Differential pressure transmitter

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