Transmitter indication problem

What position are the isolation and bleed valves in?

Hi, MKashi

to resolve your issue, need this details

What is the range of the dp xtmrs, elevation, and the type of measurement is it dp level, dp flow, dp pressure.

Regard's

>have checked the under pressure zero their was a difference of +2" H2O

What does "the under pressure zero" mean ? What state are your various valves in to get zero pressure?

How could there be zero pressure at both ports if you have not yet blocked both line valves and opened the equalizer valve, (which appears to be your next step)?

>but when depressurized it, found -2" H2O.

The 3 valve manifolds typically used with DP transmitters do not 'depressurize'. The equalizer valve equalizes the pressure between the high side and the low side so that there is no differential pressure, hence the zero (under those conditions) should be 0.00" differential. There might well be static pressure on both ports at that time.

When you say 'depressurize', is some port open to atmosphere, or is 'depressureize' your word for 'equalized' pressure?

>Apply zero Trim, but when checked the under pressure zero that was 9" H2O.

That sounds like you used a HART or keypad function to correct the -2" H2O to 0.0" H2O.

What isn't clear is what state the transmitter and valves are in when you 'checked the under pressure zero'. What steps do you take to achieve conditions of 'under pressure zero'?

>Checked the static pressure of transmitter while it is depressurized it was Reading 4 PSi.

It is somewhat disconcerting to change engineering units from inches water column to PSI. Are you re-configuring the transmitter to read its local display in two different eng units? Or how does it work to get both inches water and PSI ?

do a calibration on the transmitter, by following your cal. procedure you will understand your transmitter better and hopefully you can fix your problem