RTD Current Source

Discussion in 'General Electronics Chat' started by pdunc, Mar 23, 2010.

  1. pdunc

    Thread Starter New Member

    Feb 26, 2010
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    0
    Good morning,

    I am currently in the process of building a circuit to excite an PRT (100 ohm @ 0 degC) with a constant current.

    This current should be < 1mA and remain constant regardless of load resistance.

    I have found two circuit designs;
    • I've seen the use of a LM317 but this seems to have a minimum current output of around 2 mA - do current regulators go lower than this?
    • Otherwise I found a design which used two op-amps with a precision referance voltage (so a voltage regulator would be used instead) to generate the constant current.
    My question is really should I use an integrated current regulator with a low output current or regulate a voltage (~ 2.5 V) and convert this to constant current?

    The common method of using a bridge circuit will not provide adequete accuracy for the scope of the measurements.


    Thanks in advance,


    Peter
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    What kind of accuracy do you require?
     
  3. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Take a look at an LM334 -- that might suit your needs.
     
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  4. pdunc

    Thread Starter New Member

    Feb 26, 2010
    8
    0
    It's really just to satisfy my project requirements, I need the transducer to be as linear as possible over a 0 - 100 deg C range.

    I am performing dynamic compensation on the circuit to try to negate the delay in heat transfer through a thermowell. The more linear the response, the less error in my estimations.

    I expect it to be non-linear to some extent; ways of correcting that error will be discussed, but they do not really come under the scope of the project.

    Hope that makes sense :rolleyes:

    @ someonesdad - Thank you for the suggestion, I am reading through the data sheet at the moment.

    Thanks again,

    Peter
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    pdunc likes this.
  6. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    A current regulator diode might work for you. There are lots below 1mA such as 1N5283 to 1N5296. You will still need to provide a voltage to bias everything.

    Regards,
    Ifixit
     
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  7. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Thanks for the note, ifixit -- I had never heard of one of these. Here's a link where you can see the i-V curve.
     
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