I have a problem with a differential transmitter DPT (measurement of LPG flow by a flat orifice of the Column to storage through pumps) which transmits the measurement to the regulator on DCS as shown in the diagram.

The problem is that the PDT does not follow the setpoint (Manual or Auto). the valve closed and the flow rate remains displayed, once 10t/h or more. If I open the valve for example: 40%, the flow rate indicates more than 70℅.
I did the calibration of the PDT on site and we coordinated with the flow rate indication on DCS. I adjusted it precisely. and once it was placed, the problem persists.
I tried to isolate the Auto valve completely, but the flow rate remains indicated 5 or 6t/h !!
knowing that:
Pdt scale: 0 to 2500mmH2O
Regulator tag: FIC4204 from 0 to 100t/h (see diagram).
Valve tag: FV4204.

 

What is the pipe size, details of your orifice plate, and the vendors meter calculation, and piping layout

 

Here u are datasheet of the orifice plate

 

Make sure all air is flushed out of the instrument tubing using the bleed vents at the transmitter, to insure stable zero setting.

5% to 6% error at low flow conditions is not uncommon in operating plants.

 

you need to zero trim on a constant pressure with no flow...

 

I would re-phrase that to, "you need to zero trim at no flow to eliminate the differential offset at no flow".

To my knowledge all industrial DP transmitters have a HART function to call the output zero (4.000mA) at whatever pressure 'remains' at zero flow.

The offset can be due to a tilted, non-vertical installation that puts more pressure on one diaphragm than the other.
-

 

you need to zero trim on a constant pressure with no flow...

What I said here should still be valid...