Riken Keiki SD-705RID Explosion Proof Gas Detector

Riken Keiki Model SD-705RID Explosion-Proof Infrared Gas Detector (ExdIIBT4X)

The Riken Keiki Model SD-705RID is a diffusion-sampling infrared (NDIR) gas detector engineered for continuous monitoring of combustible hydrocarbon gases in hazardous Zone 1 and Zone 2 maritime and offshore environments. Housed in a heavy-duty, flameproof cast aluminum enclosure rated to ExdIIBT4X, this unit eliminates the sensor poisoning and zero-drift issues common to traditional catalytic bead sensors in oxygen-deficient or silicone-rich marine cargo spaces.

The SD-705RID utilizes a dual-wavelength non-dispersive infrared optical bench to deliver a linear 4–20 mA DC analog output proportional to the Lower Explosive Limit (% LEL) or volume concentration (% vol) of target hydrocarbons such as methane, propane, and butane.

Model Details

• Manufacturer: Riken Keiki Co., Ltd. (Tokyo, Japan)
• Model Series: SD-705 Series
• Exact Model Number: SD-705RID
• Manufacturer Part Number (MPN): SD-705RID (Specific sensor range suffix applies per target gas configuration, e.g., CH4 0–100% LEL or HC 0–100% LEL)
• Explosion-Proof Rating: ExdIIBT4X (TIIS / Japanese Industrial Standard Flameproof Enclosure)
• Sensor Principle: Non-Dispersive Infrared Absorption (NDIR)
• Sampling Method: Natural Diffusion

Terminal Allocations & Wiring Interface

• Terminal 1 (+24V): 24V DC Power Supply Positive Input
• Terminal 2 (0V / GND): 24V DC Power Supply Common / Negative Return
• Terminal 3 (4–20mA +): Analog Signal Output Positive (4 mA = 0% LEL, 20 mA = 100% LEL)
• Terminal 4 (COM / Shield): Signal Common / Cable Shield Drain Wire Termination
• Internal/External Earth Lug: M4 Brass/Stainless Steel Grounding Screw

Compatibility

• Riken Keiki Indicator & Alarm Racks: RM-580 Series, RM-585 Series, RM-5000 Series, and GP-88 / GD-K88 legacy conversion panels (via 4–20 mA input cards).
• Universal Marine Safety Systems: Compatible with any standard 24V DC, 3-wire 4–20 mA PLC, DCS, or Integrated Automation System (IAS) including Kongsberg K-Chief, Wärtsilä NACOS, and Consilium Salwico gas control modules.
• Calibration Accessories: Riken Keiki Calibration Cap (Model: CAL-CAP-705) and Magnetic Calibration Key (allows non-intrusive zero/span adjustment without opening the flameproof cover).

Features

1. Poison-Immune NDIR Optics: Dual-wavelength infrared sensing eliminates sensor degradation caused by silicones, lead compounds, hydrogen sulfide H2S , and halogenated hydrocarbons frequently encountered in engine rooms and cargo pump rooms.
2. Operates in Inerted Environments: Unlike catalytic pellistor sensors that require at least 10–12% oxygen to oxidize gas, the SD-705RID accurately measures hydrocarbons inside nitrogen-purged ballast tanks, double-hull spaces, and inert gas (IG) blanketed cargo tanks.
3. Non-Intrusive Magnetic Calibration: Equipped with an external magnetic switch interface, enabling engineers to execute zero-air and span-gas calibrations in hazardous Zone 1 areas without obtaining a hot-work permit to unbolt the flameproof housing.
4. Fail-Safe Optical Diagnostics: Built-in microprocessor continuously monitors infrared source intensity and optical path contamination, dropping the loop current below 2.0 mA to trigger an immediate fault alarm at the bridge or cargo control room (CCR).
5. Heavy-Duty Marine Construction: Flameproof ExdIIBT4X aluminum housing with IP65 ingress protection withstands high-vibration pump rooms, salt-spray exposure, and extreme ambient temperature swings.

Applications

• LNG / LPG Carriers & Chemical Tankers: Continuous hydrocarbon monitoring in compressor rooms, cargo pump rooms, void spaces, and cofferdams.
• FPSO & Offshore Oil/Gas Platforms: Perimeter and process skid gas leak detection in Zone 1 hazardous locations.
• Dual-Fuel & LNG-Powered Vessels: Gas Valve Unit (GVU) enclosures, double-walled fuel gas supply piping, and engine room ventilation exhaust ducts.
• Petrochemical Refineries & Tank Farms: Storage tank dike areas, loading gantries, and solvent recovery units.

Frequently Asked Questions

What is the difference between the Riken Keiki SD-705 and the SD-705RID?

The standard SD-705 utilizes a catalytic combustion (pellistor) sensor, which requires oxygen to operate and is susceptible to sensor poisoning from silicones and sulfur compounds. The SD-705RID uses a Non-Dispersive Infrared (NDIR) optical sensor, making it immune to catalyst poisons and capable of detecting hydrocarbons accurately in oxygen-deficient or nitrogen-inerted spaces.

What does the ExdIIBT4X certification on the SD-705RID mean?

ExdIIBT4X designates a flameproof enclosure (Exd) certified for Group IIB gas atmospheres (such as ethylene, propane, and general hydrocarbons) with a T4 temperature class (maximum surface temperature will not exceed 135°C). The X suffix indicates specific conditions for safe use, such as adhering to certified flameproof cable gland requirements and ambient temperature limits (-20°C to +50°C).

How is the 4–20 mA output wired on the SD-705RID?

The SD-705RID uses a 3-wire (or 4-wire isolated) configuration. Connect +24V DC to Terminal 1, 0V DC common to Terminal 2, and the 4–20 mA signal return to Terminal 3 (with Terminal 4 acting as the signal common/shield). An output of 4 mA corresponds to 0% LEL, 20 mA corresponds to 100% LEL, and a current below 2.0 mA indicates a transmitter fault.

What gas flow rate is required when calibrating the SD-705RID?

During zero and span calibration using the Riken Keiki calibration cap, apply zero air (or 99.99% Nitrogen) and span calibration gas (typically 50% LEL Methane or Isobutane) at a steady flow rate of 0.5 liters per minute (L/min). Over-pressurizing the optical cell with higher flow rates will skew the infrared absorption reading and cause inaccurate span calibration.