Measuring principle of a resistance sensor

The resistance sensor (RTD element) is normally evaluated by measuring the voltage drop across the sensor through which a measuring current flows. The voltage change ΔU_t measured in the EL3204-0162 is proportional to the resistance change ΔR_t.

In the ratiometric measurement, a constant voltage is applied to the resistor R_ref and R_t (Fig. Ratiometric measurement). More important, however, is the temperature stability of the reference resistor R_ref. In general, therefore, a ratiometric measurement as the quotient of two quantities with the same disturbance overlapping does not affect the measurement. The ratiometric value is therefore independent of the supply voltage. The measured value R_t is determined here via the ratio of the voltage drop at U_ref and U_t and the reference resistance R_ref.

R_t = R_ref x U_t / U_ref

In general, a ratiometric measurement as the quotient of two values with the same disturbance overlapping does not affect the measurement. A ratiometric value is therefore independent of the supply voltage.

The voltage change is proportional to the resistance change and hence also to the temperature change.

Wiring of the RTD input channels Due to this measuring principle (resistive temperature sensor), a sensor may not be connected in parallel to two or more input channels!