Rtd Wiring Configuration - Advantech iDAQ-815 User Manual

3.3.2

RTD Wiring Configuration

RTDs are offered with 2-wire, 3-wire, or 4-wire configuration.
Figure 3.5 RTD wiring configuration.
Because the RTD input actually measures the resistance of the RTD, any lead-wire
resistance will contribute to the measurement errors. However, measurement errors
can be reduced by using different excitation and circuit topology for each configura-
tion shown above.
In 2-wire configuration, the lead-wire resistances cannot be separated from the RTD
resistance. Therefore, 2-wire RTDs have the least accurate measurement result, but
are the least expensive solution.
In 3-wire configuration, the lead-wire resistances can be compensated if their values
match for each lead. With 3-wire RTDs, a much more accurate result can be obtained
compared to 2-wire RTDs with a little more cost.
In 4-wire configuration, the lead-wire resistances can be compensated completely
and yield the best accuracy, but 4-wire RTDs are the most expensive ones.
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