The Thermal Flow Switch Monitor is based on the principle of thermal dispersion. A typical configuration uses two Temperature Detectors set within the tip of the sensor. One Temperature Detector is heated a few degrees above the other one. As the process medium flows over the tip of the sensor it disperses some of the heat from the heated Temperature Detector. The delta temperature is a function of flow velocity and converted into electronic signal. The open collector changes state once the set point has been reached.