Change a 2 wire RTD to a 3 or 4 wire

Discussion in 'General Electronics Chat' started by Gibson486, Mar 10, 2015.

  1. Gibson486

    Thread Starter Member

    Jul 20, 2012
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    12
    If I add my own resistors, could I theoretically turn a a two wire RTD into a 3 or 4 wire RTD? In the real world, it is probably not feasible to do this (just buy a 3 or 4 wire RTD?), so this question is purely academic.
     
  2. Reloadron

    Active Member

    Jan 15, 2015
    964
    232
    In a word yes. You may want to give this a read. The actual RTD itself is a 2 wire device. How you configure it can be 2, 3, or 4 wire.

    Ron
     
  3. Gibson486

    Thread Starter Member

    Jul 20, 2012
    199
    12
    Thanks! Maybe I am over thinking this. If this use of 4 wire and 3 wire only if you are making connections from beyond the pcb where it is located? If the RTD is on the PCB where the measurements are being converted, I am guessing that all these R values really become negligible?
     
  4. Reloadron

    Active Member

    Jan 15, 2015
    964
    232
    You would be guessing correctly. :)

    The RTD itself is no more than a leg in a bridge. If the bridge is nice and local so to speak you will have 3 fixed resistors and the RTD all comprising the bridge circuit. There is no lead resistance to speak of or compensate for. However, if I have my 3 fixed resistors on a board but my RTD (the sensor) some distance away then in some cases the lead resistance comes into play. This is where 3 and 4 wire measurements become important. This is especially true with low resistance RTDs.

    Ron
     
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  5. Gibson486

    Thread Starter Member

    Jul 20, 2012
    199
    12
    Thanks! Saved me about an hours worth of time! Many Thanks!
     
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