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Need help with my transmitter

Discussion in 'General Electronics Discussion' started by kodomo, Jun 22, 2013.

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  1. kodomo


    Jun 22, 2013
    I have some problems with device in my work,
    the device read analog input 4-20mA with voltage transmitter about 24V.
    But my transmitter signal output is 4-20mA with voltage transmitter below the device requirement so my device can't read it. so I must amplified the voltage transmitter without change the current.
    actually it's not transmitter, it's a sensor that connected to 0-5 V to 4-20mA converter, the converter is IC that has 5V VCC.
    what can i do to make the transmitter connected to the device? The device has 24V VCC

    I really keen to get some helps with it

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Sorry, your description is a bit confuse.
    Can you show a diagram how the devices and suppply voltages are connected? What kind of transmitter do you actually use? 4-20mA or voltage output?

    A 4-20mA transmitters output should be re<d by an ammeter, not as a voltage. You can convert the curent to a voltage by adding a series resistor into the current loop and measuring the voltage (V=I*R) across the resistor, but I'm not quite sure that is your concern.
    Last edited: Jun 22, 2013
  3. kodomo


    Jun 22, 2013
    Thanks for answering Harald, sorry my description is a bit confuse.

    The transmitter use 4-20mA output signal, the analog input from my device also read 4-20mA signal. But it will read the output signal from transmitter as long as the signal have around 14-28V voltage, and my transmitter voltage is below that requirement. So I need to amplified the voltage without change the current.
  4. davenn

    davenn Moderator

    Sep 5, 2009
    hi komodo,

    you still didnt really answer Harald's question

    what is the transmitter RF, IR Laser, RS232 something totally different ????

    if RF what frequency?

    show the circuit diagram as its really next to impossible to understand what you are talking about without a diagram :)

  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    @dave: I think he's talking about a 20mA current loop, the "transmitter" is his current source. No RF or light involved.

    I still don't get it: the transmitter's output signal and the input of your device match perfectly (both are 4-20mA).
    Do you realize that the output voltage of a 4-20mA transmitter is completely irrelevant? The transmitter is a current source (within limits) and as such forces the current regardless of the burden (resistor). Therefore if you hav a low burden (low resistance), you will see low voltage. If you have a high burden (high resistance), you will see a high voltage. The voltage is limited only by the max. output voltageo f the transmitter (compliance voltage).
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