SP Series Thermal Dispersion Flow Switch

SP Series is a thermal dispersion flow switch is a precise flow sensing device for liquids. The principle of operation is based on heat transfer. The SP thermal dispersion flow switch is offered with a variety of output types and materials of construction. No moving parts make the SP series a long lasting and high value flow switch.


The SP series is a thermal dispersion flow switch product line that responds to liquid flow and provides a switch output. Based on the principle of heat transfer, the SP thermal dispersion flow switch consists of two temperature sensors. One temperature sensor is the reference and measures the temperature of the fluid where the thermal dispersion flow switch probe is immersed. The second temperature sensor is heated by the SP using constant power. This creates a temperature difference between the two temperature sensors. As the flow rate of the fluid increases there is a cooling effect due to the fluid moving past the heated sensor. The more flow, the more the cooling. A reduction in temperature difference between the two temperature sensors indicates that the flow rate exceeds the user adjustable set point. When the flow rate drops there is less cooling, which causes an increase in the temperature difference. The SP series thermal dispersion flow switch is available in several versions with choices of lengths, materials of construction and output types to meet a wide range of application requirements..


  • No moving parts, solidstate performance and reliability
  • 1~59″ per second (150cm/s) measuring range for water; 1~118″ (300cm/s) range in oil
  • 304SS, 316SS, PVDF and polypropylene wetted parts
  • Maximum operating pressure up to 1,450psi (100bar)
  • Choice of NPN/PNP, N.O. or N.C. relay, or SPDT relay output
  • Standard and custom extended insertion lengths
  • Standard or high temperature, explosionproof units available
  • LED indication of flow status
  • Marine certified unit available



  • Detect positive flow to control downstream process
  • Ensure machinery safe operation with detection of coolant flow


  • HVAC
  • Petrochemical
  • Power
  • Food processing
  • Pharmaceutical
  • Many others

Datasheet: EN