Answer / prince

RTD's work on the principle of RESISTANCE. The two working
wires might have different lengths, so different resistance.
Third wire is used for compensating the extra resistance so as
to get accurate o/p. Third wire is in parallel connection with
one of the wire. In 4 wire RTD, the compensation is more.

Answer / carl_ellis

It is correct that an RTD indicates a change in temperature
by a change in resistance of an element.

The change in resistance must be monitored electronically
and any circuit connected to an RTD will include copper lead
wires which will add resistance to the circuit.

The problem is not that the lead wires will have different
lengths, the problem is that any copper lead wire has some
resistance which will contribute to a voltage drop from the
source current and appear to be the resistance of the RTD
element. Any contribution of resistance to the measurement
is an error.

Two lead wires connect to the RTD element and a 3rd lead
wire is used to compensate for the added lead wire
resistance so that the lead wire resistance is eliminated
and only the RTD resistance is measured and used to
calculate temperature.

Carl Ellis
Measure First

Answer / rathod mukesh r

If 2 Wire rtd use , The distance is more between remote location (Rtd) And dcs panle then error occur in reading of temperature. Means if wire length is increases then its own resistance also increase so proper reading is not transmited via 2 Wire. In 3 Wire rtd these error is remove using compensasion lead.

Answer / yugesh shah

3rd wire is called compensation wire , when RTD is installed
far away from control room or where we get indication then 2
wire RTD fails to send appropriate sign al due to
temperature effect or atmospheric changes so 3rd wire is
helpful to send error free signals or resistance

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