A resistor temperature device (RTD) trip unit is described. The RTD monitors thermal conditions at an industrial process location, such as in a nuclear reactor. Resistance of the RTD varies in accordance with temperature at the monitored process location. An amplifier circuit produces an output signal, corresponding to the variations in RTD resistance, which signal operates a plurality of relay circuits. The relay circuits variously report process conditions such as failure, the obtaining of a preselected level, etc. Additionally, metering provides a continuous analog indication of thermal conditions at the monitored process locations. To correct for non-linearity inherent in the RTD resistance slope, a recursive feedback path is coupled between the RTD amplifier stage and an RTD current source, such that a decreasing resistance slope produces a complementary increase in current supply to the RTD. The result is a linear output signal from the RTD amplifier.