Thermatel® Model TD1/TD2 flow/level/interface 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 TD1/TD2 the latest in thermal dispersion switches.

Operating Principle

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.


- Pump protection
- Cooling water/Cooling air
- Chemical feed pumps
- Relief valve monitoring
- Lubrication systems
- Exhaust flow monitoring
- Seal leakage
- Safety showers/Eyewash stations
- Leak detection
- Vacuum pumps seal fluid
- Paint flow
- Sampling systems
- Analyzer flow


- Temperature compensated to provide repeatable alarm under varying process temperatures
- Continuous diagnostics detect sensor fault
- Non-linear mA output signal can be used for trending, diagnostics and repeatable flow/level indication
- Detects minimum flow or presence / absence of flow
- Easy / fast calibration
- Excellent low flow sensitivity


- Hot tap retractable probe
- Hygienic design
- NACE construction
- Window to view alarm status
- Integral or remote electronics
- Flow body for very low flow detection


+ Product Catalog
+ Instruction & Operating Manual