Thermal Flow Switch

There are many applications where knowing whether there is flow or no-flow conditions of a fluid in a pipe is important.  A thermal flow switch is an option to consider to provide such positive indication of flow or no-flow conditions.  Detecting flow conditions also can be accomplished using a electromechanical paddle type flow switch.  However, a thermal flow switch operates without any moving parts and therefore is more reliable.

A thermal flow switch, also known as a thermal dispersion flow switch,  is a precise flow sensing device.  The principle sensing method is that of heat diffusion.  According to Wikipedia, “The operation of thermal dispersion flow sensing is attributed to L.V. King who, in 1914, published his famous King’s Law revealing how a heated wire immersed in a fluid flow measures the mass velocity at a point in the flow. King called his instrument a “hot-wire anemometer”. However, it was not until the 1960s and 1970s that industrial-grade thermal dispersion devices finally emerged.”

A typical thermal flow switch consists of two temperature sensors.  One sensor measures the temperature of the fluid when the sensor probe is immersed in the liquid.  The other temperature sensor is heated by a constant power.  This creates a temperature difference between the two sensors.  Temperature difference is an inverse ratio to the flow velocity.  Advantages of the thermal flow switch over the electromechanical paddle style flow switch includes:

  • Higher sensitivity,
  • Less installation restrictions,
  • No moving parts or wear and tear.

In addition, with a therm flow switch:

  • Different materials can be used for a wide range of fluids,
  • Probe length is easily made to a specific application,
  • Multiple types of output signals are available.

Application and use of the thermal flow switch can be found in water power plants, steel production, marine use, food processing, pharmaceutical manufacturing, semiconductor manufacturing and many industries where flow sensing in pipes is required.

For a further look at a thermal flow switch product line you can visit our SP series product page or download the SP series flow switch sales catalog.

For more information on the SP series thermal dispersion flow switch product line you can contact us at 815-632-3132.

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