View Full Version : 4-20 Ma
licensed to chill
06-29-2008, 06:07 PM
How can i convert a 12 vdc power supply to produce 4-20 ma?
Need something simple to test actuators and vfd signal inputs.
I don't really want to spend the money on a fluke process meter because i don't do controls all the time.
06-29-2008, 06:16 PM
Buy a Kele signal generator. Think mine was about $150 a few yrs ago.
06-29-2008, 06:52 PM
I also have one of the Kele signal generators. It works very well.
Here is a link with more information on it
06-29-2008, 07:28 PM
I have used one from ACT. It is in the same price range as the one from Kele.
07-01-2008, 02:17 AM
Volts / Resistance = Current
Volts / Current = Resistance
12V / 0.004A = 3000 ohms
12V / 0.02A = 600 ohms
Use a potentiometer with range 600 to 3000 ohms in serial to produce the wanted current. Tho it would probably be easier to just buy the one from Kele or ACT
07-01-2008, 08:14 PM
You have to also take into account the impedance of the input on the device you’re testing, which will vary between devices.
If you’re willing to whip out a soldering iron, the AD694 is a cheap IC that can do exactly what you want. With a few parts and a DC power supply (ie battery) it will drive a 4-20ma signal that will be consistent with different devices attached to it.
Here is a diagram.
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