Series-ST51

Supported Applications

The FCI ST51 Series is a thermal dispersion mass flow meter designed for the measurement of biogas, digester gas, methane, natural gas, flue gas, and other hydrocarbon mixed gases. The series also supports air, compressed air, and nitrogen applications.

• Wastewater treatment plant digester systems
• Biogas production and recovery
• Landfill gas recovery
• Cogeneration power systems
• Coal mine methane recovery

Operating Conditions & Performance

The ST51 series measures mass flow with a standard accuracy of ± 2% reading ± 0.5% full scale, or an optional high-accuracy calibration of ± 1% reading ± 0.5% full scale. Repeatability is specified as ±0.5% reading.

• Measurement Range: 0.3 SFPS to 400 SFPS (0.08 mps to 122 mps)
• Ambient Temperature: 0 °F to 140 °F [-18 °C to 60 °C]
• Process Operating Temperature:

The standard ST51 model supports process temperatures up to 250°F [121°C]. The ST51A variant extends this capability to 350°F [177°C]. Specific ferrule and packing materials impose lower limits: Teflon ferrules are rated to 200°F [93°C], while stainless steel ferrules support up to 500°F [260°C] in specific configurations.

• Pressure Ratings:

Ratings depend on the connection type and material. Compression fittings with Teflon ferrules are rated to 150 psig [10 barg]. Stainless steel ferrule compression fittings and retractable packing glands (with graphite or Teflon) support up to 500 psig [34 barg]. Optional ball valves offer ratings of 1000 psi [70 bar] max for standard-duty models and 1440 psi [99 bar] max for heavy-duty models.

• Response Time: 50 ms or greater

Configuration Options

Housing, Mounting, and Electrical Connections

The series offers integral or remote transmitter configurations with blind housings or local digital displays. Housing materials include standard aluminum (epoxy coated) or optional 316 stainless steel.

• Enclosure Rating: NEMA 4X [IP67] / IP66
• Electrical Connection: Dual conduit ports available with either 1/2" Female NPT or M20x1.5 entries

Process Connections and Insertion Lengths

The meter is designed for insertion into pipes ranging from 2" to 24" (51 mm to 610 mm) diameter.

• Compression Fittings: 1/2" MNPT or 3/4" MNPT with Stainless Steel or Teflon ferrule
• Packing Glands: Retractable packing gland options in 1/2" MNPT or 3/4" MNPT with Graphite or Teflon packing material
• Insertion Lengths: Adjustable from 1" to 18" (25 mm to 457 mm)

Sensor and Output Options

The flow element utilizes a -FPC type with FCI patent-pending flow conditioner. Wetted materials include 316L stainless steel body with Hastelloy-C22 thermowell sensors.

• Outputs: Dual 4-20 mA (configurable for flow rate and/or temperature), Pulse output for total flow, RS-232C Communication Port
• Communication Protocols: HART (v7) I/O, Modbus (485 RTU/ASCII)

Approvals and Special Options

The series supports various hazardous location approvals including FM/FMc Class I Div 1 Groups B,C,D; ATEX/UKEX II 2 G Ex db IIC T6...T1 Gb, II 2 D Ex tb IIC T85°C...T300°C Db; and IECEx. Additional certifications include EAC/TR CU, NEPSI, CRN No.: 0F0303, and SIL 1 compliance (ST51A only).

• Options: Vortab flow conditioners, AVAL application modeling software

Key Product Differences

The ST51 series includes the standard ST51 model and the extended-temperature ST51A variant. The primary distinction is process operating temperature capability (ST51 to 250°F [121°C] vs. ST51A to 350°F [177°C]) and maximum remote distance for integral configurations (ST51 up to 50' [15 m], ST51A up to 100' [30 m]). The ST51A also carries a SIL 1 compliant rating with a Safe Failure Fraction of 78.5% to 81.1%, whereas the standard ST51 does not list this compliance.

Model configurations are defined by an ordering code structure specifying transmitter type (blind vs. display, integral vs. remote), power supply voltage range (DC or AC), pipe installation orientation, process connection style, insertion length, gas media calibration conditions, and agency approvals.