selection of Pressure trasnducers! 1

[Ali768]

Hello

I am designing a vertcial test rig i.e. vertcial pipe with shor horizontal run before the air-water enters in vertcial pipe to see the flow patterns (rig will work at atmospheric pressure). I am intertested in measuring the pressure along the pipe . any suggestion about the pressure measurment with transducers what type? reference gauge or abs? out supply?

 

[btrueblood]

Are you trying to measure pressure transients/fluctuations, or the mean/average pressure? I.e. why are you measuring pressure, what is your experiment or apparatus being used for? How will you be recording the transducer output, and at what speed or sample frequency? If you can give us a bit more info., we can help you much more effectively. Generally, you should use the most accurate transducer your budget will allow for.

 

[Ali768]

Thankyou btrueblood .....for your response.

Yes your are right i will be measuring fluctuations and mean average pressure along the test section.Apart from usual two phase flow variables I will be looking at the flow pattern identification through pressure fluctuations.I intend to do with LabView rest is still at planning stage.

Your help will be appreciated in this regard.

Ali768

 

[btrueblood]

Okay, so you don't need super-high freq. response, but some (say a few hundred Hz) would be nice. Stainless steel diaphragm for water service.

My preference lately for doing water flow testing has been the MSI transducers, that are available from

http://www.digikey.com.

These are stainless steel diaphragm, piezoresistive sensors (silicon bonded to backside of diaphragm). Because of laser trimming and all the usual neat silicon foundry tricks, they offer as good as 1/4% accuracy at very reasonable prices. They have these down to 25 psig range, and lower pressures to 1% accuracy.

I would just get gage (atmosphere-referenced) pressure xducrs, and measure barometric pressure if that is important to you. If you need more precision for differential measurements, use a differential transducer.

As long as you use shielded cable and good shielding practice (follow your DAQ board mfg's advice), a voltage-output transducer works fine, even around the usual "noisy" equipment like pumps/compressors. Use 4-20mA output if it's a really noisy shop (welding, RF noise), but realize your calibration will vary depending on the tempco of the current measuring resistor. If precision/accuracy are important, buy, borrow, or build a good deadweight prover for doing your own calibration (end-to-end) of your pressure instrumentation.