Thermatel® TD1/TD2 Thermal Dispersion Switches

The Thermatel^® Model TD1/TD2 switch is utilized in flow, level and interface applications.

The TD1/TD2 is popular for pump protection, specifically low flow detection with the unique spherical tip design, to prevent pumps from running dry.

Continuous diagnostics with fault indication, temperature compensation and fast response time make the TD1/TD2 the latest in thermal dispersion technology.

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.

The THERMATEL sensor consists of two RTD elements. One is the reference and the second is heated to a temperature above the process temperature.

The electronics detect the temperature difference between the two elements. The temperature difference is greatest in air, then decreases when cooling occurs due to a change in media.

An increase in the flow rate further decreases the temperature difference.

The set point is adjusted for the switch to alarm at the desired temperature difference. Once the set point is reached, the relay will change state.