Abstract: A temperature sensing device is disclosed in which the temperature sensing element is a semiconductor diode. The reference supply current for the diode is derived from an offset voltage regulator in such a way that power source fluctuations appear as common mode inputs to an operational amplifier. The operational amplifier controls a voltage controlled oscillator. The output pulses of the oscillator are counted over periodic time intervals of predetermined length to produce periodic counts which correlate to temperature. The device is designed in the preferred embodiment for use on commercial alternating current power lines where the length of timing for temperature sensing, the interval between readings and switching between multiple sensors is controlled by the power line frequency.