Abstract: In a temperature measurement region, a thermocouple and a reference voltage source in turn supply voltages via solid state switches to the center-tapped primary winding of a transformer. The output voltages of the transformer secondary winding are applied via an analogue-to-digital converter to a crystal-clock-regulated digital processing unit that obtains the difference of positive and negative voltages derived from the thermocouple signal, the positive and negative voltages derived from the reference voltage, for subsequent ratiometric processing. The switches are operated by a switch control unit that responds to signals arriving via electrically-isolating transducers from switch control latches that receive switch control outputs from the digital processing unit.