Scientific Hanging Position and System Integration Guide for Mining Laser CO and Methane Sensors

In coal mine excavation, tunneling, transportation, and electromechanical chamber areas, carbon monoxide (CO) and methane (CH₄) are two main hazardous gases. Real-time monitoring of their concentrations is critical for ventilation efficiency, power-off interlock reliability, and personnel evacuation. The National Mine Safety Administration has repeatedly emphasized that improper sensor installation is a major cause of monitoring blind spots, data distortion, and potential accidents.

Nexisense mining laser CO and methane sensor series use tunable diode laser absorption spectroscopy (TDLAS) technology, offering high selectivity, fast response, low drift, and intrinsically safe explosion-proof features, specifically designed for complex underground environments. This guide outlines 2025-standard scientific hanging positions, key monitoring area layouts, system integration compatibility, project application experiences, and maintenance recommendations from a system integrator and project implementation perspective, helping B2B clients achieve high safety compliance and system stability throughout the project lifecycle.

Technical Features and Regulatory Basis of Mining Laser Gas Sensors

• GB 3836.1-2010 “Explosive Atmospheres – Part 1: Equipment General Requirements”

• MT/T 1134-2019 “Mining Laser Methane Sensors”

• AQ 6203-2020 “Mining Laser Methane Sensors”

• JJG 1136-2017 “Verification Regulation for Laser Methane Detectors”

• Coal Mine Safety Regulations (latest revision)

Core technical advantages include:

• TDLAS laser spectroscopy with high selectivity for CO and CH₄, minimally affected by H₂S, CO₂, dust, or humidity

• Range coverage: CO 0–1000 ppm, CH₄ 0–5%vol (or 0–100%LEL)

• Response time T90 ≤10 s

• Intrinsic safety explosion-proof mark: Ex ib Ⅰ Mb

• Wide temperature operation: -20℃–+50℃ (some models -40℃–+70℃)

• Built-in automatic compensation for temperature, humidity, and pressure

Hanging Position Standards for Mining Laser CO Sensors

Recommended Installation Height and Scientific Basis

Recommended hanging height: 1.5–1.8 m from floor (human breathing zone)
Scientific basis: CO density (1.25 kg/m³) is close to air (1.29 kg/m³); in micro airflow underground, it distributes evenly or with slight stratification. This height best represents actual exposure risk.

Key Monitoring Areas and Position Requirements

• Mining workface: 5–10 m from coal wall or working head, return air side preferred

• Return roadway: 10–15 m from return air inlet or airflow junction, straight section

• Transport roadway: near conveyor head/tail drive and transfer points

• Electromechanical chambers: transformer, switch, charging, hoist rooms, positioned on airflow side or above equipment

• Main haulage roadways: one monitoring point every 100–150 m

Installation Avoidance Principles

• Avoid direct airflow from local fans or ducts (may dilute readings)

• Maintain ≥300 mm from roof to prevent dripping onto optical window

• Avoid strong vibration equipment (e.g., shearer, transfer machine)

• Do not hang on moving equipment (monorail crane, track car)

  
  

Hanging Position Standards for Mining Laser Methane (CH₄) Sensors

Recommended Installation Height and Scientific Basis

Recommended hanging height: ≤300 mm from roof (prefer near roof)
Scientific basis: CH₄ density (0.717 kg/m³) is much lighter than air, tends to accumulate near roof in still or low-flow environments, reflecting gas accumulation risk most accurately.

Key Monitoring Areas and Position Requirements

• Coal face: ≤10 m from coal wall (high-gas mines ≤7 m), return air side preferred

• Tunneling face: ≤5 m from heading, return air side preferred

• Return roadway: 10–15 m downstream of airflow junction, straight section

• Goaf corners: independent installation, at roof-coal wall junction, sensor axis inclined 10–15° from horizontal

• Sealed goaf areas: 1–2 m outside sealed wall; add sensor at high points if needed

• Gas drainage pipelines and pump stations: sensor near pipeline entrance and surrounding pump area

Special Layout Considerations

• High outburst zones: add dedicated sensors at highest void points

• Old goaf sealed walls: 1–2 m outside, add inside if necessary

• Geological zones: increase density near faults/folds

System Integration and Compatibility Guidelines

• Communication interface: RS-485 Modbus RTU (standard), baud rate 9600/19200 selectable

• Analog output: 4–20 mA (2-wire/3-wire), linear mapping to range

• Alarm output: two-level dry contacts (Alarm 1/2)

• Power: 9–24 V DC, intrinsically safe supply

• Data: real-time concentration, percentage of range, alarm status, fault codes, optical intensity, internal temperature, compensation parameters

Integration recommendations:

• Connect to KJ series safety monitoring systems via Modbus RTU, clear device addressing, up to 32 per bus

• Critical interlock points: use both 4-20mA hardware and Modbus software alarms for redundancy

• Long-distance communication (>800 m) requires repeater or opto-isolation modules

• Recommended dual sensors per monitoring point (CO+CH₄ or redundant), for data comparison and fault detection

  
  

• Wireless expansion: mining LoRa or 4G/5G modules for retrofit or cableless areas

Installation, Calibration, and Maintenance

• Perform gas test (zero gas + standard sample) after installation to verify readings

• Mandatory verification: 1 year (legal metrology)

• Routine calibration: every 3 months for zero and span, record environment

• Clean optical window monthly with 75% medical alcohol; avoid organic solvents

• Protection: IP65+ dust/water shield to prevent coal dust and moisture

• Moving working face: reposition and calibrate when advancing 50 m or production requires

Typical Project Applications

High-gas coal mine longwall monitoring upgrade: Nexisense laser CH₄ (corner + return) and CO sensors (transport + electromechanical chambers), RS-485 to KJ725 system. Over 24 months, gas exceedances reduced ~79%, CO alarm response ~11 s.

Shaanxi large-scale tunneling gas protection: laser CH₄ near heading 5 m and return side; independent corner setup; transport road CO sensors every 120 m. Remote calibration and diagnostics, 3 years without safety incidents.

Metal mine underground diesel exhaust monitoring: CO sensors at 1.6 m in transport and electromechanical areas, integrated with ventilation interlock, compliant with safety inspection standards.

FAQ

1. Why hang CO sensors at 1.5–1.8 m? Density close to air, this height represents breathing zone exposure.

2. Must CH₄ sensors be near roof? Yes, ≤300 mm captures accumulation risk.

3. Can corner CH₄ sensors mount on hydraulic support? No, vibration affects optics; use independent bracket ≥500 mm away.

4. Can CO and CH₄ share same bus? Yes, via different Modbus addresses.

5. How to protect sensors in dripping areas? Use IP65+ shield and check drainage regularly.

6. Need frequent calibration? Mandatory once a year; routine every 3 months, drift minimal vs catalytic sensors.

7. How to achieve redundancy for interlock? Use both 4-20 mA hardware and Modbus software alarms.

8. Support remote diagnostics? Yes, check optical intensity, internal temp, compensation parameters remotely.

Conclusion

Scientific hanging positions of mining laser CO and CH₄ sensors are fundamental for effective underground gas monitoring, affecting blind spot coverage, data representativeness, and interlock response. Nexisense series offers high-selectivity laser detection, rigorous explosion-proof design, and broad interface compatibility, providing stable and reliable sensing solutions for high-gas mines, outburst-prone mines, tunneling faces, and electromechanical areas.

For coal mine safety monitoring upgrades, intelligent working face construction, tunneling gas protection design, or ventilation system retrofit, contact Nexisense technical team for layout drawings, protocol manuals, selection spreadsheets, on-site commissioning guidance, and regional project references to ensure safe, efficient, and compliant underground gas monitoring projects.