This insertion-style flow meter has no moving parts and is available in probe lengths for installation into pipe diameters from 2.5 inches to 24 inches [63 mm to 610 mm]. It is easily connected into the pipe via a ½ inch or ¾ inch NPT compression fitting. ST51 uses constant power thermal dispersion drive technology, with a slightly heated sensor, which uniquely provides a subtle drying effect on the sensors that results in effective measurement in moist gas applications.

The ST51 Series electronics are housed in rugged, IP67 rated enclosure with dual conduit ports in either NPT or M20 threading. The instrument comes standard with dual 4-20 mA, NAMUR NE43 complaint outputs and a 500 Hz pulse output. The model ST51A adds HART or Modbus, a higher process temperature service range, a SIL compliance rating and extended warranty. The transmitter/electronics can be integrally mounted with the flow element (probe) or be remote mounted to best match your installation situation. The complete instrument carries global Ex agency approvals for Division l/Zone 1 installations.

The ST51 flow sensing element features precision, platinum RTD in small diameter, “equal-mass,” all-metal thermowells to provide superior accuracy, repeatability, and fast response.


  • Landfill gas recovery (LMG)
  • Wastewater treatment plant digester
  • Coal mine methane recovery
  • Air/compressed air with totalized flow
  • Livestock and dairy farm on-farm biogas recovery
  • Biogas: biomass fermentation and recovery
  • Biomass gasification

Key Facts

  • No moving parts
  • Non-clogging
  • Small, compact design
  • Easy to install
  • Dual 4-20mA outputs
  • Dual line LCD readout
  • Ex hazardous location approvals

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