Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Resistance Temperature Detectors

  1. Nov 13, 2015 #1
    Can someone explain three wire and four wire RTD circuits in terms of how the lead resistances affect the voltage output

    ##V_o = \frac{R_3 V_s}{R_2 + R_3} - \frac{R_4 V_s}{R_1 + R_4}##

    Also, in the case of a three wire, what is the purpose of Lead C?

    Attached Files:

    • 3,4.png
      File size:
      26.4 KB
  2. jcsd
  3. Nov 14, 2015 #2


    User Avatar
    Gold Member

    First you need to understand Kelvin Contacts:

    Then,the Kelvin Bridge.

    Then either you will have your answers or more questions. :smile:

    The whole goal is to eliminate errors caused by measuring the voltage drop across the current carrying wires that are feeding the sensors.

    Maybe you understand that already, but I think you just need to work through the math of the two circuits to see how the errors cancel.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook