Testing a 4-20mA output card.

Hi Guys,

this has got to be an easy one to answer, but I simply can't get it to work.

I've got a D/A card set up to output 4-20mA (I think) and I'm trying to work out how to wire it up with a resistor (again I think) so that I can confirm that its doing what I expect it to.

Now, the card has the following terminals on it.

Vout, Isink, AGND, 12V out

I though it would be a simple matter to connect a 100 ohm resister across Isink and AGND and then measure the voltage across the resister with a multi meter and see what's happening.

As you've probably already worked out nothing did.

I then tried 12V to Isink with the resistor, and I got a constant voltage drop.

I really am stuck now. There must be a way of testing this setup, but I can't figure it out.

Can anyone help please.


Peter Nunn.

Reply to
Peter Nunn
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Try 12V --- [ RESISTOR ] - Isink.

12V = I Source Isink= 4-30 ma Current Sink or other range

Reply to

If you mean a resistor from 12v to isink and you measure across the resistor then that sounds right.

A constant drop representing something in the 4..20mA range?

You say you are testing the card - maybe it is faulty or you are not driving it correctly.

Reply to

Not very helpful, are they. Firstly, most 4-20 mA signals are based on 24 VDC. As mentioned in an earlier discussion, the corresponding voltage is

1-5 Volts. For an output it doesn't really matter. A typical load is up to 600 Ohms. That would correspond to 12 V. Perhaps your system only has a 12 volt supply. That would be rather low and probably not acceptable in an industrial application. I'm guessing that you are expected to put your load resistor between the Vout terminal and the Isink. Vout provides the driving power and Isink regulates the amount of current through the load and down to the common neutral, AGND.

Try it and let me know. I would stick to resistors in excess of 200 Ohm so you don't short anything.


Reply to
Walter Driedger

I am not familiar with 12 volt 4-20ma loops, normally they are 24 volt. A 250 ohm resistor (249 is close enough) is used to make 1-5 volts.

Without more information on your card, I can make a lot of guesses, but it looks like 12V connects to Isink with the resistor, then Isink to AGND. Then, maybe the resistor goes between Isink and AGND.

We really need more >Hi Guys,

Reply to

Some cards also need software configuration to makes either reads Voltage or current. I know the terminals are there, but you might need to download some software to your card initially.

Reply to
Akheel Soltan


Siemens S7-300 6ES7331-7KF01. You don't load any software, but you do need to select your input type (V/mA) and range in STEP7. IIRC, some of the

*really* old input modules required configuration software.

Not sure, but Siemens, AB, ABB and Honeywell all seem to specialise in this area - and I'm sure there are others. ;-)


Reply to
Cameron Dorrough

Thanks for this information.

I'm still not having any luck with this card. Its an Advantech PCI-1720 and I'm begining to think that its faulty.

I can't even get it to output voltage at the moment.

If I hook up the 12 volts via a 100 ohm resister to Isink and from there tho ADGND via a 100 ohm resistor I get a bit over 20mA flowing.

Without the link to ADGND I get 4mA.

I simply can't get this to work anywhere between or under my control.

Any other ideas?



snipped-for-privacy@home.com wrote:

Reply to
Peter Nunn

Yokogawa CS3000 DCS, CARD AAM11 "Current/Voltage Module", The card is not Plug N play, it needs config software downloaded, you can either download the current input config or voltage input config. Why have a complex solution for a simple problem? because they can.



Reply to
Akheel Soltan


That's the info we needed. My catalog tells me that you have the following ranges available:

0 to +5V 0 to +10V +/-5V +/-10V 0 to 20mA (sink) 4 to 20mA (sink)

Voltage output is between "Vout" and "AGND" and needs no external connections, so you might like to get this going first. Check the jumper settings and make sure you disconnect *everything* else from the DB37 before trying it.

The card does *not* source voltage, but does have one on-board +12V (80mA) supply available on Pin 2. Since the max current loop voltage is 50V, I would suggest forgetting about the +12V and:

  1. Get hold of a 24VDC power supply and a 1k or 1.5k resistor (to act as the "load" - 100ohms is a bit small).
  2. Connect +24VDC to the "Isink" terminal via the 1k resistor.
  3. Connect -24VDC to the "AGND" terminal.
  4. Measure the voltage across the resistor as you change your output and use ohm's law to calculate the current flowing.

Good luck! Cameron:-)

Reply to
Cameron Dorrough

Thanks again Cameron,

turns out that the drivers that ship with the card are no good. Got the latest drivers from the web site, and away we go.

Quite a pa>Peter,

Reply to
Peter Nunn

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