#WishIKnew – What’s a differential pressure transmitter?


When you have a question about process automation that needs a short answer, let us know with #WishIknew and #Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.

I wish I knew what a differential pressure transmitter is!

A differential pressure transmitter or other (DP) devices get a lot of use because of their flexibility and simplicity. Even though you can find better options in the market today, many field engineers still stick to the good old DP.

A differential pressure transmitter is composed of a sensing cell and a transmitter. The cell has two pressure chambers separated by a diaphragm. We call one chamber the high-pressure side and the other the low-pressure side, but you don’t have to take that literally. It just tells you the direction of the impact that pressure will have on the output signal.

courtesy of Wolf Process Automation

So imagine you have a process with -20 bar to 20 bar and no pressure in either chamber. At that point, the signal will read 12 milliamps (mA), representing 0 bar, 50 percent of the range. If you apply pressure on the high-pressure side of the differential pressure transmitter, then the value will rise towards 20 mA, giving you a positive reading. On the other hand, if you apply pressure to the low-pressure side, then that drives the signal towards 4 mA and a negative reading.

You can find several options for converting the pressure in the sensing cell to an electronic signal – piezoresistive (strain gauge), piezoelectric, resonant, and capacitive methods all will get you there. And that’s it for now, all you need to know about a differential pressure transmitter!

This video will tell you more about differential pressure transmitters:


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