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0 - 2.5V to 4-20mA Transmitter

Joze Gerdenc
Prodigy 30 points
Other Parts Discussed in Thread: XTR111

Dear Mr. Collin Wells
I'm a new member here and I hope you can help me :)
I would like to transform input voltage 0 - 2,5V to 4 to 20mA. I tried to change Rset to 1,5k but it's not ok.
Results when Rset = 1,5k:
Uin = 2,5V -> Iout = 20mA
Uin = 1,25V -> Iout = 13,33mA
Uin = 0V -> Iout = 6,67mA

Can you give me some advice which elements on the schema above do I have to change (new values)?

Thank you!
Best regards
Joc
  • 0
    TI__Guru 64125 points

    Hello Joc,

    I suggest you use the XTR111 in the configuration shown below:

    Here's the simulation file:
    XTR111_2p5V_to_4-20mA.TSC

     

  • 0 in reply to Collin Wells
    Prodigy 30 points

    Mr, Collin

    Thank you for your quick reply and for useful solution. What kind of resistors should I use? Metal film resistors with small tolerance? Is it possible to design circuit with zero and span trimmer potentiometer (in the case of adjustment)? Can you check and comment the circuit (zero, span trim pot. - schema below)?

    Best regards!

    Joc

    XTR111_2p5V_to_4-20mA_span_zero_joc.TSC

  • 0 in reply to Joze Gerdenc
    TI__Guru 64125 points

    Hi Joc,

    The trim circuitry you've included is correct and will be useful to calibrate each system. 

    You should choose resistors based on your application's requirements.  If you need a high accuracy system, then you'll likely have to buy more expensive resistors and trim potentiometers.  If the application needs to maintain high accuracy over temperature then you'll need to purchase low-drift resistors and trim potentiometers.

  • 0 in reply to Collin Wells
    Prodigy 30 points
    Mr. Collin,
    Thank you for your advises about choosing appropriate resistors.
    I found out that I have to paying attention on the Rload too (the power supply have also influence on Rload_max). If the power supply is 12V then resistance of Rload can be a maximum of 500 ohms.


    Now I have to draw the PCB :)


    Thank you very much!
    Best regards
    Joc