The SP-150 Thermal Flow Sensor is based on the principle of thermal dispersion. A typical configuration uses two detectors set within the tip of the sensor to detect the difference in temperature between two set positions within the probe. As the liquid flows over the tip of the sensor it disperses some of the heat and is converted by the internal circuit into an electronic signal to change the state of the enclosed collector.
Output is NPN/PNP and the working termperature -20 to +80 DegC. The sensor has a stainless steel housing and led indication of velocity.