Issue in Analog input in PIC16F877

Discussion in 'Embedded Systems and Microcontrollers' started by ecaits, May 20, 2014.

  1. ecaits

    Thread Starter Member

    Jan 6, 2014
    52
    0
    Dear Friends,

    I am working on PIC16F877 with hi-tech c compiler.
    I have used 0-5V analog input but in field, I am getting 4-20mA output.

    Can I use 4-20mA as analog input or I need to convert 4-20mA to equivalent 0-5V??? How can I use it???

    Plz suggest me.

    Nirav
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
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  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi.
    You could use a 250R resistor to terminate the current loop.
    For 20mA you will get a voltage of 5V across the 250R.
    At 4mA a voltage of 1V, which you could subtract within the program.

    Giving a span of 4Volts
    E
     
  4. paulfjujo

    New Member

    Mar 6, 2014
    20
    3
    hello,

    You just have to check:
    - if you can connect the Cold point of 4-20mA signal to your 0V PIC power supply, together.
    without galvanic insulation problem..
    - if you don't allready have other device in this 4-20mA loop
    - if your 4-20mA loop is an Active loop (deliver the current , so not a passive loop)
    - in case of 250R brocken, you can get all Voltage of the loop (12V or 24V!)
    on ADC input..
     
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