The thermal switches are based on convective heat transfer. One sensor is at the process temperature and the other is being heated by a constant power. As the flow rate increases, the temperature difference between the sensors decreases. A set point is established so when that specific temperature difference is reached the relay changes state. This can be on either increasing or decreasing flow or flow/no flow. When used in a level or interface application it is primarily the thermal conductivity of the fluid that will provide the difference in heat transfer.
Thermal Dispersion Flow/Level/Interface Switch
The thermal switches provide a new level of performance and reliability not found in previous switches. Continuous diagnostics with fault indication, temperature compensation, narrow hysteresis and fast response time make the switches the latest in thermal dispersion switch technology.