Need Help

Discussion in 'The Projects Forum' started by sirish, Apr 5, 2006.

  1. sirish

    Thread Starter New Member

    Apr 5, 2006
    Hi Friends,

    I am using a temperature transmitter connceted to my heat exchanger.
    The temperature transmitter gives me current output in 4-20 ma current range.
    I want to convert this 4-20 ma current signal to voltage in the 1-5 volt range.
    for which i will use the circuit :

    I need to convert this voltage in the range of 1 to 5 volt so that i can perform data acquisition on pc.
    But i need a adc circuit which will take this input vtg and then interfacing it to the pc at the parallel port.
    Plzzzzzzzzzz i need help in designing the adc circuit for the same.
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    You'll find that resistors are also current-to-voltage converters. Use a small enough value so the measuring device doesn't have to develop too many volts for the 20 mills current.

    A dual op amp will finish the conversion. Use the first with a pot on the non-inverting input to take the 4 mill level down to zero. The voltage will, of course, be inverted, so the second op amp will re-invert and add any necessary gain/cut to the signal level.

    As for the A to D, why reinvent the wheel? There must be over 1000 different ones on the market. Or just use a microcomputer with the little bugger built in. Anything over 10 bits will do.