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Thermatel® TG1/TG2 flow/level/interface switches with din rail

Thermatel® TG1/TG2 provides a two-wire, intrinsically safe circuit between the probe and remote din rail enclosure. The flow/level/interface switches provide a new level of performance and reliability not found in previous switches. Continuous diagnostics with fault indication, narrow hysteresis and fast response time make the TG1/TG2 the latest in thermal dispersion switch technology.

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The product

Thermal dispersion switch 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.


  • Easy field calibration – pre-calibration fro factory on request
  • Variable flow or flow / no flow detection of gases and liquids
  • Excellent low flow sensitivity
  • Continuous diagnostics detect sensor fault
  • mA output provides repeatable indication of flow rate and fault detection
  • Process conditions up to +850 °F (+450 °C) and 6000 psi (413 bar)


  • Low flow body for very low flow rate detection
  • Hygienic design
  • NACE construction

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.


ATEX Ex ia
EAC (GOST) Ex ia
SIL SIL 1 (1oo1)

Other approvals are available. Consult factory for more details.

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