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I want to connect a 4 wire RTD PT100 in a wheatStone Bridge. I tried searching on internet but only up to 3 wire configurations in bridge are available or circuits using other ADS IC's are available. But I want to do it in a Bridge Configuration.

Can anyone suggest how I can do it?

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    \$\begingroup\$ Why do you want to do this? Are the other resistors co-located with the Pt100 or elsewhere? Are they normal resistors or something else? \$\endgroup\$ Feb 22, 2014 at 15:29
  • \$\begingroup\$ i want a way to connect a 4 wire RTD in one of the arm of the WheatStone Bridge. is it possible or no with 4wire RTD? \$\endgroup\$
    – Priyanka
    Feb 23, 2014 at 16:46

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It isn't a good idea to use resistive temperature sensors this way because of the large change in resistance will delinearize the bridge whether current fed or voltage fed. Devices like strain gauges bearly change their resistance at all and can be ok as a single active element in a bridge but not RTDs.

So, use the three wire connection and use a constant current feed. This is the most accurate method for RTDs. If you do a double measurement of the two wires feeding the sensor you can determine cable volt drop. If volt drop is minimal or constant use a two wire connection.

Because your RTD is four wire use an instrumentation amplifier or use it in 2-wire mode or 3-wire mode.

Your current source should be referenced to your ADC ref voltage if using an ADC with an inaccurate reference.

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  • \$\begingroup\$ how to use a 4 wire RTD in 2 or 3 wire mode? it needs a suppy through 2 of its wires right? \$\endgroup\$
    – Priyanka
    Feb 23, 2014 at 16:41
  • \$\begingroup\$ and is it possible to connect a 4 wire RTD in a WheatStone bridge ? or not possible? if not possible then which is the gud IC which can take input from 4 4-wire RTDs? ADS1246 can take only upto 3 RTDs..so can u suggest one with low cost but shoud take input from all the 4 RTDs \$\endgroup\$
    – Priyanka
    Feb 23, 2014 at 16:44
  • \$\begingroup\$ or is it possible to connect the 4 wire RTD in another bridge format like kelvin ? please suggest. I have to find a way of connecting a 4 wire RTD in a Bridge \$\endgroup\$
    – Priyanka
    Feb 23, 2014 at 16:48
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    \$\begingroup\$ You will have two errors in 2-wire mode and 1 error in 3-wire mode. The common error is due to progressive non-linearities of a bridge with large changes in one value (the RTD). You don't get this when more than two elements are active BTW. The other error is the cabling resistance so just use 1 connection for the excitation return wire and use the two connections on the other side of the gauge for (A) power feed and (B) return signal to instrumentation amplifier/differential amplifier. \$\endgroup\$
    – Andy aka
    Feb 23, 2014 at 18:07
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    \$\begingroup\$ ADS IC? Not sure what you mean but I'd consider using an instrumentation amplifier like an AD8221 - it needs to be massive input impedance to avoid another error and this will do the job but, it needs a neg power rail unless the mid point voltages of the brisge are above a couple of volts - check the data sheet. \$\endgroup\$
    – Andy aka
    Feb 23, 2014 at 18:09

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