signal converter

Discussion in 'General Electronics Chat' started by Ramasule, Nov 6, 2004.

  1. Ramasule

    Thread Starter Member

    Nov 6, 2004
    12
    0
    Greetings, my problem is this.
    I am interfacing a plc with a vfd. The problem I am having is that the vfd signal out is a 4-20ma loop and the plc card takes a 0-5 volt signal.

    What could I use to convert a 4-20ma signal to a 0-5 volt one.
    (I was thinking of a Fet and a battery and having the 4-20 control the voltage through put through the fet.)

    Any suggestions welcome
    Thank you,
    Derek
     
  2. Iodem_Asakura

    Senior Member

    Sep 14, 2004
    140
    0
    I think it easier and better for you to use an optocoupler.
     
  3. Ramasule

    Thread Starter Member

    Nov 6, 2004
    12
    0
    optocoupler hmm that sounds interesting, anything that i could use that you would find in basic electronics kit.
    (also scematic if you can include one pls thanks)
     
  4. Iodem_Asakura

    Senior Member

    Sep 14, 2004
    140
    0
    Well, here is a transistor optocoupler. Read it to see if it works for you.

    If the on current is higher than 20 mA, you must build an amplifier so it amplifies the 20 mA to a level that can make the optocoupler to turn on, but that amplifies the 4 mA to a level below that, so the optocoupler remain turned off.

    By the way, sorry for been late :p , i have been a little busy.
     
  5. Ramasule

    Thread Starter Member

    Nov 6, 2004
    12
    0
    No problem, can u check the file again though im reading it as corrupted.
    Thanks.
     
  6. Iodem_Asakura

    Senior Member

    Sep 14, 2004
    140
    0
    Try to download it again, 'cause i downloaded it from my post again, and it is ok.
     
  7. Ramasule

    Thread Starter Member

    Nov 6, 2004
    12
    0
    Must be my security settings.
     
  8. Iodem_Asakura

    Senior Member

    Sep 14, 2004
    140
    0
    Ok, tell me your mail, and i'll send you the file. :)
     
  9. dimas_lilik

    New Member

    Nov 10, 2008
    1
    0
    can you email scematic for to convert a 4-20ma signal to a 0-5 volt one
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    I'll make one in a bit. Basically an op amp current to voltage convertor along with a summer to set the 0 point.

    Here is the starting point.

    [​IMG]
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    OK, this will do it, you can use variables potentiometers to replace the odd resistances.

    [​IMG]

    Since most op amps do not go rail to rail you will need supply voltages that exceed your output range, as well as a plus and minus power supply.

    Have you really looked at the dates of the original posts? You really should have started a new thread, those guys are long gone.
     
    Last edited: Nov 10, 2008
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