3 RTD temperature probe
16
3.5 Circuit types
3.5.1 Two-wire circuit
The two-wire circuit is the simplest circuit type for RTD temperature probes.
Three and four-wire circuits are also used to enable more accurate measurements.
With two-wire circuits, the line resistance influences the measurement result. This means that to obtain
accurate measurement results, the line resistance must be deducted or needs to be corrected at the
evaluation electronics; please see chapter 5.1.1 "Correcting line resistances", Page 22.
Minor deviations in the line resistance may occur due to fluctuations in temperature and the production
process.
3.5.2 Three-wire circuit
With three-wire circuits, it is possible to partially compensate the influence of the line resistances as a
result of temperature fluctuations. An additional measuring circuit is formed, which can be used as a ref-
erence. For this to work, the wire features must be identical.
3.5.3 Four-wire circuit
With a four-wire circuit, two measuring circuits are formed. The deviations (temperature-dependent sup-
ply line resistances, differing line resistances, etc.) can be fully compensated.
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