Absolute XMTR Using for Styrene Recovery

range is 0-100mmhg, it should comply with another 3 xmtr reading like 80to 60 in mmhg but it's not so we need to calibrate it

• There are two pressure gauges on a vessel showing different readings. Which one does one believe <rhetorical question - NNTR>?
• Has this plant been the subject of a HazOp Study?

Have the instruments recalibrated off-line by qualified instrumentation technicians. Rationalise the instrumentation installed so that only one set of readings is obtained, and go forward from there.

I'm stuck on a couple issues. 1 - I haven't used Foundation Fieldbus so I don't understand how it displays locally vs on the DCS; 2 - I don't know what a 'capillary pad' is or how it uses or connects to the transmitter.

It is my understanding that the value the transmitter measures is available to the DCS, the range is only established for display purposes. The measurement is not limited, like a 4-20mA is limited, the measurement covers the entire the span of the instrument. So, it isn't clear to me, what a 'range of 100mmHg' really means.

Some issues in general with absolute pressure measurements:

1) When an absolute pressure transmitter is open to the atmosphere,
it measures barometric pressure. The "standard" for sea level is 760mmHg A, but even a sea level measurment varies with the local weather. Elevation above or below seal level is evident in the measurement.

When you "deplug xmtr @ atmosphere and read 748mm at DCS" that's normal and typical of what it would read. It shows you're a little above sea level.

A reading this close to atmospheric barometric pressure indicates to me that the pressure transmitter is working properly.

2) Error:
The Druck 610 is an Intrinsically Safe portable pressure calibrator.
If it applies -100mmHg (gauge, with respect to atmosphere), then the 3051 TA should read

748mMHg A minus 100mmHG g = 648 mmHg

When the transmitter reads 657 mmHg A, there is an error of 9 mmHg

3) Mounting position (whether the transmitter is upright or on its side or at some angle from the vertical)
Mounting Position Effects, per Rosemount's spec:
"3051T Zero shifts up to 2.5 inH2O (6.22 mbar) (4.67mmHg), which can be calibrated out. No span effect."

If "calibrated out", then all measurements must be made with the transmitter in the same mounting attitude (like zero check at atmosphere).

The 4.7mmHg of mounting error could be a potential error contribution.

4) It isn't clear exactly what the transmitter reads in-situ, in its installed location.
If the reading is 100mmHg A, give or take, then one thing to look for is leaks. It doesn't take much of a leak to suck in atmosphere and get from 80 mmHg A to 100 mmHg A

5) Foundation Fieldbus has a bunch of function blocks, some of which that can be used to jigger the output value. Have you checked through the FB settings?

your issue no1-in FF ( fieldbus foundation) generaly use XD scale for output scale suppose your xmtr calibrated 0-100 mmhg & if you want use 25-75mmhg you no need to re-calibrated at set everything , just apply figure in XD scale output scale 0%=25mmhg & 100% =75mmhg so what you want it done by XD scale, now if incase if Process value will go below 25mmHg like 24,,,20,,15,,,1mmhg you can read at DCS same figure but it will come as alarm ,so means your 0-100mmHg you scale will give you reading this is speciality of XD but out of XD PV will in alarm condition,

your issue2-capillary pad means simple , capillary tube attach diagphram type xmtr,

would you like to give guidance how to calibrate Absolute xmtr for 0-100mmhg & specially if calibration range is 0-2 kg/cm2 ( absoute) ?............

it will greatfull

Which brand and model absolute transmitter?

What is the link to the FF version manual for the transmitter?

Is this what you call a capillary pad?

How close is the absolute reading to local barometric pressure when your seal's diaphragm is at atmospheric pressure? How much error is there?