Differential pressure transmitter used to measure flow

One of the common applications for differential pressure sensors is to infer the flow rate of a fluid moving through a pipe, by passing that fluid through a restriction (called an "orifice"). The pressure drop across that restriction then becomes a representation of the flow rate. By measuring that pressure drop and applying the necessary characterization to the signal, a measurement of flow may be obtained.

Category:

Education

Tags:

• instrumentation
• DP
• cell
• differential
• pressure
• transmitter
• flow
• orifice
• plate

[rpm750]

Hi Tony, since you are flowing a liquid through this orifice plate I'd like to see how a U tube Manometer could be used to measure the differential pressures. I work in Water-Wastewater and we have many orifice, venturis along with DP transmitters(Rosemount) to calculate flow. As a calibration check I'd like to use a manometer to verify the DPs. Thanks so much, have your study guide and love your teaching technique. I wish I could attend your class but we are on opposite ends of the us.

[BTCInstrumentation]

@rpm750 Using a liquid manometer to measure DP in a liquid process is challenging. Your manometer would need to use a liquid substantially denser than the process liquid (e.g. mercury), and then its calibration would be skewed by the weight of the process liquid on top of the manometer liquid columns. Better to use a manometer with air pressure to validate the calibration of a diaphragm-style DP sensor, then apply the DP sensor to the process application.

[SuperLex6]

Is the square root function stored in the instrument memory?

[BTCInstrumentation]

@SuperLex6 Yes, the square-root function is performed in the transmitter (instrument) itself, and the configuration for that function is stored in its memory.

[BTCInstrumentation]

@njmfzl Go to Google and search for "Socratic Instrumentation". On that site you will find links to my free textbook, which provides complete derivations of the square-root function for flow measurement, as well as many other formulae you may find helpful.

[SuperLex6]

Are you sure that it is "memory?" Or is this function done by analog solid-state components such as adders, op-amps.

Or is there in fact a processor or EPROM in the 1151 that performs a square root function. Thank you!

[SuperLex6]

I would like to speak with you about this, would that be possible? Thank you

[njmfzl]

@BTCInstrumentation can you please provide me the derivation for the formula DP = (Flow)^2 or you can provide me any link where i can find such information. Many Thanks

[BTCInstrumentation]

That's correct: triple the flow rate, you get 9 times the pressure drop. Quadruple the flow rate, you get 16 times the pressure drop. Pressure drop is proportional to the *square* of the flow rate.

[nomisme]

just curious.. correct me if i am wrong. you said if you power triple the flow rate you will get pressure increase by a factor of 9 , not by 6?