FST200-Series

Supported Applications

The Omega FST-200 Series thermal dispersion flow switches provide reliable low or no-flow detection for relatively clean, non-coating media. The series is designed to monitor liquids and gases in general-purpose applications where the sensing tip remains submerged and liquid temperature stays constant throughout the process.

• Liquid examples include deionized water and acetic acid
• Corrosive liquids and gases
• Pulsating flow from 10 to 100 pulses per minute

The sensors are not recommended for use with electrically charged application liquids; the liquid being measured may need to be electrically grounded for most reliable operation. These products are not designed for human applications and should not be used in hazardous locations.

Operating Conditions & Performance

The FST-200 Series operates within a process temperature range of 32° to 140°F (0° to 60°C) and an ambient operating temperature of -40° to 140°F (-40° to 60°C). The switches utilize thermal dispersion technology, incorporating two temperature probes where the flow reduces the temperature of a heated probe.

• Measurement Range (Liquids): .04 to 3 fps (.012 to .91 mps)
• Accuracy: ±5% of setpoint at constant temperature and flowrate; repeatability is ±.5% of set point @ fixed temp.
• Response Time: 1-10 seconds (data sheet notes 10 sec after initial 30 sec warm up)
• Pressure Rating: 150 psi (10 bar) @ 25°C, derated @ 1.667 psi (.113 bar) per °C above 25°C
• Fluid Properties: Fluids from 0.4 to 1.2 specific gravity, 1 to 300 cp

The series supports a maximum supply voltage of 36 VDC (power supply range: 12-36 Vdc @ 70 mA). The relay output is rated at 60 VA, 1A max.

Configuration Options

The FST-200 Series offers configurable dimensions and materials to accommodate various pipe sizes. Short sensors (3.0" / 76mm) are used in pipes or ducting from ½" to 1-1/2", while long sensors (4.5" / 114mm) are intended for 2" and up.

• Wetted Materials: PP-PPS (Polypropylene-Polyphenylsulfone) or PVDF
• Cable Material: Polypropylene or PFA, depending on the model configuration
• Process Connection: 3/4" NPT (or ¾" G/Rp metric threads)
• Output Signal: Selectable NO/NC states via a SPST relay output
• Cable Lengths: Standard length with options for extended lengths by adding “-25” (25') or “-50” (50') to the part number; maximum cable length is 305 m (1000')

The series includes specific fittings, such as FT-51 and FT-52, for use with 76 mm (3") sensors in pipe/tube IDs from ⅛ to ½". For metric threads, a 3/4" FKM gasket must be installed.

Key Product Differences

The series distinguishes between liquid and gas configurations through model numbering and sensor length options. The primary variations are defined by the body material (PP-PPS vs. PVDF) and insertion length (Short 3" vs. Long 4.5").

• Liquid Flow Switches: Models FST-211/-212 (Short, PP/PVDF body) and FST-221/-222 (Long, PP/PVDF body)
• Gas Flow Switches: Models FST-321/-322 (Short) and FST-323/-324 (Long), with measurement ranges of 1 to .90 fps (.3 to 27 mps) as noted in the family manual
• Fittings: FT-51 uses PP wetted material; FT-52 uses PVDF, both for use with the short sensor only.

All versions feature a probe diameter of 0.7" (19mm) or 26.7 mm depending on documentation source context, and an overall length of either 3.0" (76mm) or 4.5" (114mm). The series holds CE and RoHS certifications.