Abstract: A constant power thermal property sensor compensates for changes in the temperature of the medium into which the sensor is disposed. The sensor has two side-by-side probes mounted in the medium with resistances that vary with temperature. A constant power source produces a current through the first probe and a current source applies a current to the second probe at a fixed ratio of the current in the first probe. The voltages across the probes are monitored and compared, and a signal is produced which is divided by current through the first probe. The resulting signal is representative of the heat transfer between the probes and the medium. The signal does not appreciably vary with changes in the temperature of the medium, and the medium may be a liquid, a gas, a liquid flow, a gas flow, or a combination of media. In this construction, two principal applications for the sensor are liquid level detectors and flow monitors.