4-20 Ma

[licensed to chill]

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.

[absrbrtek]

Buy a Kele signal generator. Think mine was about $150 a few yrs ago.

[jcrank]

I also have one of the Kele signal generators. It works very well.

Here is a link with more information on it
http://www.kele.com/olcat/TE7/ASG.PDF

[twisted pair]

I have used one from ACT. It is in the same price range as the one from Kele.

http://www.act-solutions.com/ICC/pdfs/psg/psg_spec.pdf

[RandEngi]

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

[orion242]

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.

http://forums.parallax.com/forums/attach.aspx?a=3066