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Example of 3-15 psi to 4-20mA Conversion

A current-to-pressure transducer is  used  to  convert  a  4-20 mA  electronic  signal  into  a  3-15 PSI pneumatic signal.

This particular transducer is configured  for  reverse action instead  of direct, meaning that its pressure output at 4 mA should be 15 PSI  and its pressure  output  at 20 mA should be 3 PSI.

Calculate the necessary current signal value to produce  an output  pressure  of 12.7 PSI.

3-15 psi to 4-20mA Conversion

We are solving this problem using standard 4-20mA conversion Formula. Click here for formula

Reverse-acting  instruments  are  still  linear,  and  therefore  still  follow the slope-intercept  line formula y = mx + b, albeit with a negative slope:

3-15 psi to 4-20mA

Calculating and substituting the slope (m)  value for this equation, using the full rise-over-run  of the linear function.

Note how the “rise” is actually  a “fall” from 20 milliamps  down to 4 milliamps, yielding a negative value for m:

Formula 3-15 psi to 4-20mA Conversion

Therefore,  a current signal of 7.07 mA is necessary to drive the output of this reverse-acting I/P transducer to a pressure  of 12.7 PSI.

Also See: Instrumentation online Tools

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9 comments

Sathish Kumar November 11, 2015 at 3:41 am

Super

Reply
Syed Muddassir December 5, 2015 at 11:56 am

How to calculate the same for direct acting i/p transducer?

Reply
karan bansal January 23, 2016 at 9:52 am

Highly beneficial knowledge

Reply
GIRISH T. January 30, 2016 at 2:50 pm

Dear Sir,
Please explain in detail about P & ID diagrams.
Thanks,
Girish T.

Reply
Jonathan Bornales June 23, 2016 at 3:29 am

the given value of 4.5 mA is 0 psi and the 19.5 mA is 100 psi . how about if 40 psi how many mA ?

Reply
Jose December 23, 2016 at 5:21 pm

Maybe we can use algebra here 19/100=x/40… X=7.6 maybe????correct me

Reply
Krishna April 21, 2018 at 12:00 pm

Super sir

Reply
Rohith December 23, 2018 at 5:46 pm

Hello Sir,
I am facing a problem as you provided formula,if it’s any mistake from my side please correct me.
My question is 15 PSI should be 20MA
Hence =(-16÷12)= -1.3333
=(-1.3333×15PSI)= -19.9999
=(-19.9999)+24= 4.0 MA
Why I get 4MA?
If any mistake please correct me

Thanks
Rohith

Reply
S Bharadwaj Reddy December 26, 2018 at 2:17 pm

Hi,
Please check the question again, the calculation provided for Reverse action, 15psi = 4mA and 3psi = 20mA.
You can use this formula for linear action > Click here

Reply

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