Diff. Pressure Transmitter

I can really try help you in this regard.Kindly try provide a more legible and bigger pic

There's not enough information in the drawing unfortunately.

Normally, a transmitter is ranged so that normal flow or pressure is at the half-range point. For example: if the transmitter is reading 10psi at normal flow, the range of the transmitter should probably be 0 to 20psi. Note the word "probably".

Alternatively, I'd just take the transmitter's range as is. In our case, we usually purchase the transmitter with the range specified for that particular loop already.

Ok.Let me assume you are looking for basic guidelines in this aspect.

I recently worked for designing and commisioning a differential pressure setup for the govt. sector rail industry.It basicallly consisted of 2 heavy duty pressure sensors which give current output and a differential amplifier.

We calibrated it to give 4mA at 0 bar and 20 mA at 4 bar.And the amplifier was configured accordingly.And linear increase for corresponding values.

What does the instrument schedule and the instrument specification sheet say?

What you exactly want to measure through this set up is not clear...Please mention thing you want to measure if you want to measure pressure drop across stainer/filter it will be in mmWC (depends on type of fluid and mesh) first collect all data and what you want to measure

then see with another view you will have your answer..

regards

sanjiv

I Guess you want the know the pressure drop at the strainer/filter. In this case, please provide the flow philosophy. From the diagram, it seems you have a by pass line, can you elaborate if this two valve are normally open or one line is open and the other would be closed and viz a viz..

The diff pressure transmitter would a low pressure range to measure the buildup across the strainer... the data for the pressure build up you should be able to get from the straiinner manfacurer... the transmitter should be able to withstand the maximum working pressure of the system.. 125 bar (i think the drawing said) not just the the 45 bar operating range. But if you have the instrument installed... then calibrate it the correct range of the purchased instrument... unless you brought the incorrect range. You may find your desired range is outside the limits of the instrument, then you would have to purchase a new instrument. It may be better to install a pressure tansmitter and wither use trip amps or the DCS / PLC sysemts if it goes back to them to set the switching alarm setpoint.

Dear Optimusprime

As suggested in some of the above replies the calibration of Diff Pressure Transmitter is done for the range of differential pressure to be measured or for the differential pressure range of the transmitter(Both not mentioned in your querry). The line pressure indicated as 125psig in your drawing will only ensures the protection of transmitter in case there is no pressure on one side of the line which for example, is the case when purging valve of one side of the transmitter is open. It may be noted that the differential pressure transmitters are prone to damage in such conditions if not rated for the full line pressure.

Now coming to your calibration querry, if you are not sure about the calibration range, ie the differential pressure across your process, you may calibrate the transmitter for full range of differential pressure. That is, keep the line pressure of your process on one side that is 125psig and on other side the pressure can the varied from 0 to 125Psig. Repeat the similar calibration for other side also. You will get two sets of calibration results. For one set of data assign negative sign. Fitting the curve between these datas will give you the calibration factor.

The factor obtained this way may not be accurate to laboratory grade, but is surely accurate to industrial grade application.

In any case please do reply whether the above suggestion is of any worth to you.

Thanks

Calibrate the transmitter to 0-10 PSID.

A clean strainer should have pressure drop in the range of 1 -3 psi.

You can alarm in the dcs when the differential pressure goes high say 6 psi and use the standby strainer to replace the plugged one.

I agree with srini.

0~ 10 PSID is the most appropriate range for measuring the DP across a strainer.

Just make sure that if you buy a transmitter for this service,it will cover the 125 psig design pressure.

I agree, that is probably a good range in which to calibrate the differential pressure transmitter for a strainer. However, focusing this much attention on a differential pressure transmitter for a gas strainer is going a bit overboard. A quick 2 second question to the designer of the system would have taken less time and been more productive. Also, in my experience, unless you have some very dirty gas, you shouldn't really have any trouble with a gas strainer. We have quite a few gas strainers and about the only maintenance we do is open them up once a year to make sure they aren't dirty. They never have been dirty. In my opinion, unless this is life critical piece of equipment it is feeding, or required by law, the whole pressure transmitter is a waste of time and money on a strainer.

hi guys!

Got a ord from our process department.

Maximum Differential pressure is 10psi. I think that would do.

Thanks for the suggestions anyway.

Ciao.......