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why to use 3 wire at RTD ?
what's the reason for
common wire ?
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Answer Posted / 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
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