FGD-4200 Fixed Infrared Methane Gas Detector Sapphire Window 100%LEL 4-20 mA Modbus

FGD-4200 Fixed Infrared Methane Gas Detector

The FGD-4200 is a fixed infrared gas detector for methane and general hydrocarbon monitoring where catalytic sensors are unsuitable, such as anaerobic digester areas, gas engine rooms and streams containing silicone or sulphide. The upgrade targets three weaknesses reported in the field: readings that shifted with humidity, optical windows that fogged and fouled, and a housing that did not survive coastal installations.

Higher Accuracy Than Previous Generation

• Accuracy improved from plus or minus 3% FS to plus or minus 2% FS with a dual beam measurement path that compensates source ageing and detector drift.
• Zero drift reduced to below 0.5% FS per 12 months, so annual calibration is realistic instead of a quarterly task.
• Humidity and temperature cross sensitivity minimised by a heated sapphire window and internal reference channel.
• Fail safe design: any optical blockage, lamp failure or signal loss drives the output to the fault state instead of silently under-reading.

Improved Detector Performance

• Response time T90 below 8 seconds, faster than the previous 20 second optical design, so leak events are caught earlier.
• Automatic optical path and lamp health check every 24 hours, with the result reported over Modbus for predictive maintenance.
• Three relays configurable as alarm, warning and fault, removing the need for an external alarm module.
• Modbus RTU registers expose concentration, sensor temperature and diagnostic counters for plant historians.
• Infrared measurement is unaffected by oxygen deficiency, unlike catalytic sensors, so readings stay valid in inert or enriched atmospheres.

Upgraded Materials and Construction

• 316L stainless steel housing with anti-corrosion coating replaces the previous aluminium body for offshore and coastal installations.
• Heated sapphire optical window resists scratching, chemical attack and condensation, the three most common causes of optical drift.
• 316L sensor chamber with PTFE seals resists sour gas and solvent vapour attack on internal components.
• Stainless steel sunshade and bracket supplied as standard, preventing UV degradation and bracket corrosion.

Technical Specifications

Typical Applications

• Wastewater digesters, gas holders and sludge treatment areas
• Gas engine rooms and biogas upgrading plants
• Landfill gas collection and flare systems
• Refinery and petrochemical hydrocarbon storage
• Marine and offshore process modules

Calibration and Maintenance

Infrared sensors are calibrated with methane or propane standards at mid span. Because the measurement is optical, bump testing every three months is usually sufficient, with a full calibration annually. Replacement sensor modules are pre-calibrated and can be exchanged on site.

Ordering and Support

Each detector is supplied with a calibration certificate, sensor cartridge, weatherproof sunshade, mounting bracket and operation manual. Optional items include a calibration cup, duct mounting kit, remote display and HART or Modbus gateway. Our technical team supports configuration, bump testing schedules and spare sensor supply.

Contact our sales team for a quotation, datasheet or sample evaluation unit.