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Converting 4-20ma output to 2-10 vdc??

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  • Converting 4-20ma output to 2-10 vdc??

    First, I知 fairly new to PLC's. My experience is in the building automation field, similar in many respects, not so in others. I'm a bit confused on how to convert a 4-20 output signal to 2-10 VDC in the PLC world? In the past (BAS Controller) I would add a 500 ohm resistor in parallel between the output and common of the controller to convert to VDC. The specific analog card I知 using is a T1F-08DA-1. When inserting a 500 ohm resistor in parallel with the actuator ( BELIMO AFB24-MFT) signal wire and common of the actuator power I see no voltage change on the output of the actuator. I did verify the card is working properly when reading milliamps with a meter. I have a feeling the PLC card is constructed different than what I知 accustom to working with? Thanks for any help in advance!
    Last edited by BASINT; 02-12-2018, 02:31 PM.


  • #2
    If you want to get out of the analog side of it, take the value being used by the PLC to produce the 4-20 ma output and scale it to a 2-10 v output.
    Then use a voltage output card instead of a ma output card.

    You could also use an signal conditioner module like the FC-33 and convert the 4-20 ma to 2-10 vdc.

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    • #3
      The resistor should be in series with the actuator to obtain a voltage proportional to current, if I am understanding correctly.

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      • #4
        500 ohm shunt (parallel) resistor is correct. Not sure why you are not seeing a voltage change. Probably a measurement error.

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        • #5
          I will verify wiring and meter readings and check back.
          A parallel resistor is also what the actuator cut-sheet indicates.
          I have a mix of 4-20ma(VFD's) and 0-10vdc(actuators) devices and was hoping
          to utilize the current output module to drive both types of analog devices.
          Last edited by BASINT; 02-12-2018, 05:52 PM.

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          • #6
            Originally posted by BASINT View Post
            I will verify wiring and meter readings and check back.
            A parallel resistor is also what the actuator cut-sheet indicates.
            I have a mix of 4-20ma(VFD's) and 0-10vdc(actuators) devices and was hoping
            to utilize the current output module to drive both types of analog devices.
            how many devices do you intend to drive on one 4-20ma output channel?

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            • #7
              how many devices do you intend to drive on one 4-20ma output channel?
              One per channel.

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              • #8
                Originally posted by BASINT View Post
                One per channel.
                shunt resistor arrangement 'should' work for 0-10v.
                Do you need 2-10v? fc-33 may help if this is a requirement it does have zero (0-25% fs) and span (80-102% fs) adjustments -- the docs say this, I cannot locate the zero/span pots in the docs.

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                • #9
                  I misspoke, I need 2-10 and 4-20, not 0-10vdc.
                  Hoping to get time to troubleshoot this morning.

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                  • #10
                    You might call tech support. Ask about details of FC-33 ZERO and SPAN. Ask if adjusting zero/span get you a linear scaling from 4-20 to 2-10V.
                    I do not have one, and have never used the FC-33.

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                    • #11
                      The 500 ohm should work just fine. Place the resister between a 24vdc+ PS and the output of the 08da. Make sure you also have power hooked up to the 08da (v0-v1?). Hook a volt meter across the resister. You should have 2-10v for a 4-20ma of the 08da. Test this before hooking to valve. The resister should be between the 1(common) and the 3 (y1 input) on the Belimo. 24vdc+ to 3 (y1 input). 1(common) to 80da output.

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                      • #12
                        Originally posted by bsinkovich View Post
                        The 500 ohm should work just fine. Place the resister between a 24vdc+ PS and the output of the 08da. Make sure you also have power hooked up to the 08da (v0-v1?). Hook a volt meter across the resister. You should have 2-10v for a 4-20ma of the 08da. Test this before hooking to valve. The resister should be between the 1(common) and the 3 (y1 input) on the Belimo. 24vdc+ to 3 (y1 input). 1(common) to 80da output.
                        Thanks man. The above wiring does give me my 2-10vdc signal, but the actuator still is not moving.
                        I may need to bite the bullet and look into the FC-33. I also tried the above wiring in a few configuration, no dice.
                        It's almost like the signal common and P.S. common need to be separate(4 wire)?
                        Last edited by BASINT; 02-13-2018, 04:26 PM.

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                        • #13
                          Originally posted by BASINT View Post

                          Thanks man. The above wiring does give me my 2-10vdc signal, but the actuator still is not moving.
                          I may need to bite the bullet and look into the FC-33. I also tried the above wiring in a few configuration, no dice.
                          It's almost like the signal common and P.S. common need to be separate(4 wire)?
                          Does the actuator work from another source?
                          I didn't mean for you to buy the FC-33, just check with techsupport , to see if one would help.

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                          • #14
                            This setup you describe should work. 24vdc+ to Wht (3). Note resister in drawing. Control Signal (-) to 08DA. What is the full model number of actuator? Maybe needs some other input or power voltage.

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                            • #15
                              A-ha! It's working!
                              Yesterday, while bench testing, I used the same DC power supply that powered the 08DA to power the actuator(Label Indicates AC/DC).
                              After bsinkovich post, I decided to power the actuator with 24VAC instead of DC and the actuator started working like a charm!
                              Good thing all devices in the field are powered by 24VAC. In theory, a 24VDC powered actuator should work also?

                              Thanks everyone for the Help!

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