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Not Getting Measurement on 4-20mA Outputs

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  • Not Getting Measurement on 4-20mA Outputs

    I currently have a C0-12DRE-D PLC and I'm trying to get a measurement from the Analog outputs. I have configured by outputs as follows(apologies for the pictures if they don't size properly. I have uploaded them also):


    Click image for larger version  Name:	4-20_Output_1.jpg Views:	0 Size:	153.7 KB ID:	123374

    Now I have wired two ammeters as follows:


    Click image for larger version  Name:	diagram1.jpg Views:	0 Size:	56.9 KB ID:	123375

    I'm not getting any readings on the ammeters. My suspicion is that I need to connect 24V similar to what is found on page 3 in the manual for this PLC:

    https://cdn.automationdirect.com/sta...s/c012dred.pdf

    I don't want to blow anything up, so I figure it's better to ask before I do so.
    Attached Files
    Last edited by DavidH; 06-12-2019, 10:02 PM.


  • #2
    Yes, you will need an external supply
    thePLCguy

    Bernie

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    • #3
      Originally posted by bcarlton View Post
      Yes, you will need an external supply

      Thanks for the response.

      Now this raises a second question with regards to the 4-20mA analog inputs. In the manual on the same page it shows a device wired in a 3 wire configuartion. Now what happens if I have a device that has a 4-wire configuration and it has it's own independent power supply(if you look at the attached picture this paints a clear picture with regards to what I mean). Can I just connect my two signal wires straight into an input pin and the ACOM pin?

      I'm concerned about having a device that has 4-wire configuration for the input, while at the same time using the analog outputs(that have to utilize a three wire configuration according to the manual). I'm concerned that this might cause issues, since all inputs and outputs use the same ACOM pin.
      Attached Files

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      • #4
        The analog current outputs on the CLCIK CPU brick are weird (though the add-on current output modules are "normal") I think you will be ok with respect to sharing the common (which will be at "ground" potential anyway) but the weird sinking output is not always compatible with other devices.
        If you budget can stand it I'd get one of the add-on modules, or possibly a signal conditioner (or personally, switch to a Do-More BRX, though that is a big hit to the budget).
        Last edited by Tinker; 06-14-2019, 03:00 PM.

        Comment



        • #5
          The electrical connection youíve made is wrong.
          The analog output requires a ( resistive) load of usually 500ohms.
          The only load you have is the resistance offered by the ammeter. Your schematic shows a short-circuit of the analog output via the ammeter.
          You need an electrical resistor of 500ohms series with the ammeter.
          As for the built-in analog outputs, I recommend you read the plc documentation. Out of the top of my head, I believe those outputs do not require external power and use low voltage (0-5v), which means lower load resistance, so you could probably use a 100ohms instead of 500. All this is to be found in documentation.

          Comment



          • #6
            Originally posted by bcarlton View Post
            Yes, you will need an external supply
            Thanks for your advice. I just did this and it worked with the advice also recommended below.


            Originally posted by Alexandru View Post
            The electrical connection youíve made is wrong.
            The analog output requires a ( resistive) load of usually 500ohms.
            The only load you have is the resistance offered by the ammeter. Your schematic shows a short-circuit of the analog output via the ammeter.
            You need an electrical resistor of 500ohms series with the ammeter.
            As for the built-in analog outputs, I recommend you read the plc documentation. Out of the top of my head, I believe those outputs do not require external power and use low voltage (0-5v), which means lower load resistance, so you could probably use a 100ohms instead of 500. All this is to be found in documentation.
            So here is what I did. I connected 24VDC in series with a 250 ohm resistor and fed that into ammeter. From there I went to DA1I(Analog Output 1) I connected the ACOM port to ground. It now works nicely and I even managed to feed the signal into a 4-20mA signal isolator with no problems.

            Definitely a strange setup, but I guess if it works it works.

            Thanks for all your help guys!

            Comment



            • #7
              Didnít know you need external power. Thank you for sharing that. Also good job to get it going.

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