Requirement:-
Data sheet
Pressure calibrator
Multimeter
Hart communicator
Procedure:-
1) Put the controller in manual mode for control loop.
2) Connect HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
3) Isolate the instrument from the process.
4) Release both pressure and drain low and high side liquid throughout manifold drain.
5) Open both plug at seal pot
6) Top up seal liquid for low side until half of seal pot.
7) Remove tubing at high side of manifold
8) Hook up pressure calibrator at high side and isolate the vent valve
9) Hook up a multimeter in series with the signal to the DCS to measure current signal.
10) Apply pressure as per calculation when level equivalent to zero
11) Multimeter should show 4mA
12) If not, do zero adjustment at transmitter using HART Communicator
13) Apply pressure as per calculation when level equivalent to 100%Multimeter should show 20mA
If not, do span adjustment at transmitter using HART Communicator
14) After completion of the job ask panel operator to put loops back in normal mode.
15) Fill the calibration form and file it for future reference.
Note:There is many way to perform calibration for DP level but the important thing is the DP reading at HART communicator should same with the LRV and URV
Example:-
Product S.G=0.89
Glycol S.G = 1.02
A= 2000mm (measurement length)
B= 100mm (off set)
C=A+B=2100mm
Dp = pressure at high side – pressure at low side
LRV= (B x Product S.G) – (A x Glycol S.G)
= (100mm x 0.89) – (2000 x 1.02)
= 89 – 2040
= -1951 mmH2O
URV = (C x Product S.G) – (A x Glycol S.G)
= (2100mm x 0.89) – (2000 x 1.02)
= 1869 – 2040
= -171 mmH2O
Note:
Calculation for apply pressure at high side manifold transmitter
0% = (B x Product S.G)
= (100mm x 0.89)
= 89 mmH2O
100%= (C x Product S.G)
= (2100mm x 0.89)
= 1869 mmH2O
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