4-20mA schematic

Hi
I`m looking for schematic of a power supply that creates 4-20 mA current output adjustable.
I just want it to test analog cards of PLCs and simulate the transmitters for CPU in which the real transmitters have fault or dismissed.
I just want to volume the current from 4 to 20 mA
and its not important to know what is teh real current such as an indicator on the power supply .

Easy trick is to just use a potentiometer. Most cards have a 250 ohm input shunt to develop a 1-5 vdc signal on the DAC input, but some are 500 ohms. So a simple 5vdc supply and a pot from zero to 1.5K will do it. It's not exactly linear (OK, so it isn't even close to linear), but you said you don't care about accurate control, just swing the readings up and down, so this should work.

If you're uncomfortable with using a dinky little 5vdc because you may have cards with higher input impedances, then use a 24 vdc just like a loop and adjust the resistor values to suit.

Michael

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Michael Batchelor
www.IndustrialInformatics.com

Industrial Informatics, Inc.
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I'm not sure what industry you are in but back in the days when the MTL Application Notes were available on paper, our AN9003 "A User's Guide to Intrinsic Safety" had a circuit for a 4/20mA transmitter simulator that anyone could build, the current version which is only available in pdf format at present, doesn't have that circuit. If you would like a copy of the diagram, please send me an email offline and I will dig out an old copy and scan it for you.

Steve
www.mtl-inst.com
syates(AT)mtl-inst.com