Differential Pressure Transmitter Explained

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Simply put, a differential pressure transmitter is a device that measures two opposing pressures in a pipe or vessel.
To understand how a differential pressure transmitter works, we need to know some principles of pressure.
The pressure is the result of force applied onto a unit of area.
In the case of fluid and gas, this area would be the inside of a pipe, tank, vessel or other sealed housing.
Since pressure is a physical quantity, it can be measured.
The pressure is measured in one of the following five units.
- Pascal
- Bar
- Standard atmosphere or atm
- Torr
- Pounds per square inch or psi
The most commonly used measurements of pressure in an industrial fluid and gas processing environment are bar and psi.
One bar is the equivalent of the earth’s atmosphere at mean sea level.
A pound per square inch is the force of one pound on an area of one square inch.
You will most likely use these units of measurement in your work as they are commonly used and almost every manufacturer of pressure measurement devices calibrate them to these units of measurement.
Delta-P or DP is the industry-standard term for the measured differential pressure.
Delta, meaning change in, and P meaning pressure.
In addition, most people will simply call a differential pressure sensor a DP sensor or transmitter.
A DP transmitter is a pressure-measuring gauge or an electrical device that uses two elements to measure the differences of pressure in a sealed container such as a pipe.
DP transmitters will have
- A primary element
- A secondary element
- An electronics housing
The primary element will produce a difference in pressure as the flow in the pipe increases.
Different types of primary elements include
- Orifice plates
- Venturi tubes
- Pitot tubes
- Flow nozzles
- Laminar flow elements
- Wedge elements
The secondary element will measure the difference of pressure produced by the primary element as accurately as possible.
The primary element is sometimes called the high side, and the secondary element is called the low side.
The elements in a DP transmitter will have sealed diaphragms and one of several ways to convert the pressure applied onto the diaphragms into an electrical signal.
Sensors such as differential capacitance, vibrating wire or strain gauges are used to produce the electrical signal that will be sent to the electronics housing, where it is processed, converted and amplified into a current or voltage output that can be read by the control system.
The current output is commonly a 4-20 milliamp signal, or in some cases a 0 to 5 or a 0 to 10 volt signal.
The electrical output generated by the DP transmitter electronic module is linear and proportional to the actual measured Delta-P.
Depending on the range of measured pressure, a 4 milliamp signal would equal a measured Delta-P of 0 psi and a 20 milliamp signal would equal the maximum measurable value. In this case, we’ll say that the maximum Delta-P is 100 psi.
One very common way of measuring flow using a DP transmitter is for the primary element to introduce a constriction in the pipe.
Using a restrictive element on the primary side will create high and low pressure.
When the flow increases, more pressure drop is created.
As we remember, the secondary element will measure the difference in pressure created by the primary element.
These measurements are sent to the electronics housing where the signal processing is done.
By using Bernoulli’s equation, which states that the pressure drop across the constriction is proportional to the square of the flow rate, the Delta-P is then converted into units of flow.
These units of flow can be gallons per minute or cubic meters per hour. Using DP transmitters as a method to measure flow works best on fluids that are relatively clean and of low viscosity.
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#RealPars #PressureTransmitter #DPTransmitter

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[@glasslinesmadhes]

Very useful to understand the regulator principal in compressed cylinders

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Glad it was helpful!

[@mnada72]

I wished you have shown in the schematic at 6:00 how the piping connection is done to the secondary element (impulse lines)

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[@manikandanrasu4305]

Very useful video thanks lot

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[@asadabbas792]

This is great do you have courses for fluid flow analysis; control valves, tanks, orifice, pumps etc?

[@Fernando-fn2px]

@realpars Fluid stuff would be great!

[@serg.r4860]

The thing that always gets me on these transmitters is un screwing the housing to get to the wires. They are usually made of aluminum and gull & seize up.

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Very good

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That's amazing to hear, Ali! Thanks a lot for being such a champion for RealPars! Feel free to contact us if you ever have any questions. Happy learning!

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[@srinivasarohithnulu4566]

Thanks for upload.please do more videos on field instruments please please

[@realpars]

Hey! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

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great lecture

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Many thanks!

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Thanks again

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[@MBeracochea]

I have being watching many videos, they are great explanations. Could you make a video explaining the difference of an SCADA and a control through an HMI please

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Hi Mariano! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

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Supera explained... please do video on control valve and actuator types

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Hey! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

[@me_tales1406]

excellent teaching

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Glad you think so!

[@rboss9581]

Nice video!! Can you guys explain to me the formula how to calibrate a pressure transmitter and set up the value LRV and URV on a hart calibrator for a close vessel and a open vessel thanks.

[@realpars]

Hey! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

[@andrefrederickenmogne8899]

Very intresting

[@unfilteredwithprakash6970]

Detailing of manifold valve that connect at the bottom of the transmitter would be helpful.

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Thanks for sharing your feedback with us!

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Thank you

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You're welcome!

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Sir I'm learning lots of knowledge from u when u have 1000 subscribers I'm one of them 😘😘

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That's great! Thanks for your support, Amar

[@livewithnature6331]

can u kindly explain or share link, for the function of DPTransmitter connected to VFD of Pumps in Chilled Water Flow network (Closed Loop)

[@realpars]

Hi there, Thanks for the topic suggestion, I will definitely go ahead and forward this to our creator team. Happy learning!

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[@zainbsr5544]

The best educational channel, but I think the pressure transducer that you explained in the introduction to the video is the flow transformation, isn't it?

[@realpars]

Differential pressure transmitters can be used for flow measurement, level measurement, and differential pressure measurement. The masnifold shown on the pressure transmitters shown in the opening segment are most often associated with flow measurement, but can be used in all three applications.

[@rajkumarshete3638]

Good

[@kishornavin1278]

Sir, can you please provide the different types of valves and purpose in industry

[@realpars]

Hey Kishor! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

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Great videos. Explained in simple and professional manner. Keep up the good work 😇

[@realpars]

Thanks for your support, Parimal! Happy learning

[@mohammadash7072]

Would you please clarify what did you mean by " .....and one of several ways to convert the pressure applied onto the diaphragms into an electrical signal " ?

[@realpars]

The process pressure can be converted into an electrical signal through a detected change in capacitance, by sensing the pressure using compression of a special ceramic substrate, or by deflection of a piezoelectric bridge. These are all physical methods of converting pressure forces into electrical signals.

[@Guitarplayer724]

Does the paid subscription to your site offer more in-depth instruction of the topics offered here? Thanks.

[@realpars]

Hi Ono, Thanks for your comment! It indeed does, our free videos on KZbin do not follow a specific start to finish structure. Whereas our course library is specifically designed in a way where it provides all the tools needed for beginners to evolve into an advanced level through our hands-on courses. Feel free to have a browse through our course library to see which topics we cover at the moment. bit.ly/30ZrxWq Additionally, by subscribing you will have access to our Technical Team - consisting of high ranking engineers with a lifetime of experience - who are here to help you out with any questions you might have along the way! I hope this answers your question sufficiently. If you have any other questions or would like any further assistance, feel free to reach back out.

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[@realpars]

Thank you so much, Ali!

[@alejandrogl6218]

Great video thank you for uploading. Just one comment: around minute 3:14 when it says “the low increases” ... doesn’t that need disambiguating? When the flow’s speed increases, right? Because the flow’s mass rate stays constant.... Btw, if the goal was to measure dP across a strainer... wondering how it would work...

[@realpars]

There are many types of sensing elements that measure the fluid pressure upstream of the sensor (high side) and downstream of the element (low side). This differential pressure can be correlated to the flow, and the relationship is "flow is proportional the square root of the pressure differential". If I simply want to measure the pressure drop across a filter or strainer, for example, I just need to position the high-side sensing tap upstream of the filter housing or strainer and the low-side sensing tap downstream of the filter housing or strainer.

[@asadiqbal87]

upload please more videos like,ph meters,ultrasonic flow meters,rota meters,and dozzing pumps

[@realpars]

Hey Asad! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

[@punnamakhil6718]

Any measuring instrument for mean effective pressure sir

[@realpars]

If you are referring to mean effective pressure, which is the measure of an engine’s capacity to do work independent of engine displacement, then a very small pressure transducer is used that measures the cylinder pressure. Mean effective pressure determined by calculation over the entire cycle of the engine (compression, ignition, exhaust). These are typically small electromagnetic gauge pressure sensors. A good example can be found at: new.abb.com/products/measurement-products/diesel-engine-monitoring/pressure-transducer-pfpl203

[@TradefusionbySam]

Which type flow transmitter is most reliable and gives most correct values & why? please make a video

[@realpars]

Thanks for your topic suggestion, Samir! I will happily pass it on to our course library.

[@mohamedtaher3390]

Please make videos about : gas header pressure " upstream " , gas pressure " down stream ". Well head pressure and temperature .. and Riser and test Riser Pressure

[@realpars]

Hi Mohamed! Thanks for your comment and your suggestion. I will pass this on to our course developers! Thanks for sharing and happy learning!

[@AliVallil]

mmH2O is also a commonly used unit.

[@prashantgupta7923]

What is the working principle of DP transmitter

[@LouSaydus]

I really need to get back to work. I have never worked on piping in my life and will never use this information.

[@FahadAli-si5pl]

👍

[@hansajithchathuranga3307]

i want to learn DP transmitter programing.can u educate me.because i'm doing some boiler job most of the time i face problems with a DP transmitters about the programing.

[@realpars]

Hi Hansajith, Thanks for your comment and feedback! I will happily pass this on to our course developers for possible future video courses.

[@hansajithchathuranga3307]

@@realpars thanks i appreciate that 🙏

[@vundrukiran4494]

How the change in capacitence converted into electrical signal

[@realpars]

Hi Vundru, Thanks for your comment, and great suggestion! I will happily go ahead and pass this on to our course developers for a possible future video course.

[@milan6230]

What If DP is showing negative value?

[@realpars]

There are many instances where a negative value is quite normal. A common range for a DP cell is -150 inH2O to +150 inH2O. This allows for situations where the transmitter is installed what is called a zero elevation situation (wet leg, transmitter positioned below URL).

[@TheCicasica]

very nice video, but you are making a confusion between a DP transmitter and a DP Flow transmitter...and almost completely ignore DP Level transmitters :) appreciate the time and work though :)