reversing 4-20ma logic 1

[archibaldtuttle]

thanks for the help on an analyzer in previous post. i now find i have another difficulty coupling the sensors i'm considering and the equipment i want to control. the equipment expects a directly propotional 4-20 man signal but the sensor will yield an inversely proportion signal.

this is a pressure application 0-28" water column.

so 4ma on the sensor represents 0 pressure and 20ma represents 28". I need to reverse that logic so that 20ma represents 0 pressure and 4 ma represents 28". Is there a "reverser" that i can put in the current loop or that sets up its own current loop and then can output the inverse of the result onto the operating loop.

thanks

 

[btrueblood]

Double check that your pressure transmitter can't be re-calibrated to do what you want, or alternatively the controller can't be reconfigured to invert the control logic.

If you really are stuck, then look for devices like this one:

http://www.prelectronics.com/pdf/4104-2271-US.pdf

 

[IRstuff]

?? What you're describing is directly proportional? What you're asking for is the inversely proportional.

TTFN
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