Describe the importance of three wire and four wire configuration for RTD with suitable circuit diagram.
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Three wire RTD:

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Four wire RTD:

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Three wire configurations is used to help the circuit compensate for lead wire resistance, and thus provide a truer indication of the measured temperature.

Four wire RTDs provide slightly better compensation, but are generally found only in laboratory equipment and other areas where high accuracy is required. When used in conjunction with a 3-wire instrument, a 4 wire RTD will not provide any better accuracy. If the fourth wire is not connected, the device is only as good as the 3 wire RTD; if the fourth wire is connected, new errors will be introduced.. A 2 wire RTD can be used with either a 3-4 wire instrument by jumping the appropriate terminals, although this defeats the purpose and reintroduces the uncompensated resistance of the leads. To get the optimum performance, it is generally best to specify the RTD configuration. 

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