A common technique used to provide signal conditioning and measurement of the RTD is shown in the simplified block diagram on this slide, with a three wire RTD. The circuit requires a reference voltage, which does not have to be as precise as is required for thermocouples, because RTD measurement techniques are ratiometric. An external reference resistor, typically a precision element, is used to generate the reference voltage for the ADC. In the ideal case with no cable resistance, RTD resistance measurement is simply the ratio of its voltage and that of the reference. In practice, however, cable resistance drops will introduce an error in the RTD measurement, requiring the designer to use a pair of matched current sources. If the current sources are perfectly matched and the resistance in each sense conductor identical, then the effects of the cable resistance in the positive and negative sense cables will cancel each other out. While this circuit is effective in measuring RTD resistance, it does pose challenges to the designer. As will be shown next, mismatches in the current sources can introduce significant temperature measurement errors. Also, it is often desirable for the circuit to detect and report RTD shorts or opens, and protect the ADC inputs from beyond-the-rails overvoltage conditions.