Safety first! A dual-element is typically used as a back-up measurement in order to increase the reliability of the system. So, in the case one sensor fails, there is still the second sensor which provides a reliable outcome of the general measurement.
The two-wire RTD structure is the simplest among RTD circuit designs. In this construction, the single lead wires are welded to the ends of the RTD element. Because of resistance in lead wires, connectors as well as the RTD element, this construction always shows some degree of error.
The three-wire RTD construction is most common. In this construction, two wires are connected with the RTD element on one leg and the third wire links the other leg of the RTD element.
The four-wire RTD construction is the most complex of the three constructions.
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