Process signal (0-20mA) converter - input and output 2

[csgasbm]

Does anyone know if such a device exists. I'm looking for something which can read a 0-40mA (or greater) signal, convert the signal to digital and apply a formula to it. Then convert the result back to a 0-20mA analog output?

 

[itsmoked]

I do not, off hand, know of one. But check Omega.com

Also you could use a regular temp/etc controller. Drop a resistor across your 0-40mA which converts the 0-40mA to a voltage. Then using the linear input of a controller, scale the 0-40mA(now a voltage). The controller can sit there trying to control 'nothing'. Just make sure you get a controller that has a 0-20mA or the more normal 4-20mA output(option) to provide your 'converted' output.

You can use the resistor to do linear mods and also the controller. If you want some strange (non-linear) transformation...

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dbaird]

You could always use a small PLC to do this.

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[danw2]

To elablorate on Keith's suggestion:
Use a couple precision 250 ohm resistors in parallel (250 precision resistor are readily available from instrumentation suppliers) in order to convert the signal to 0-5Vdc.

Use a mid level PID controller or high level digital indicator with a re-transmitting output which can handle the 0-5Vdc input, do some conversion math on the input and re-output the input on its 4-20mA control output.

Mid level single loopers, like Honeywell UDCs have a Y=mx+b: multiply by a ratio factor, offset by a bias.

specsheet:

http://www.lesman.com/unleashd/catalog/control/control_udc2500.html

The high end UDC3500 one has an 8 point look up table capability or polynomial function:

- 8 Segment Characterizers – Two 8-segment characterizers are available that can be applied to any analog input, to Loop 1 Output or to Loop 2 Output. These can be linked together to produce a single 16-segment characterizer.

- Polynomial Curve Characterizer – A fifth order polynomial equation can be used on any one of the analog inputs.

spec sheet

http://www.lesman.com/unleashd/catalog/control/51-52-03-40.pdf

Precision Digital 690 has a look-up table and a 4-20 retransmit option
spec sheet:

http://www.lesman.com/unleashd/catalog/digital/digind_pd690.html