Nexisense Electrochemical Sensor: Integrated Solution for Toxic and Hazardous Gas and Oxygen Monitoring in the Chemical Industry

Chemical production involves a large number of toxic and hazardous gases and flammable substances, with leakage risks running through raw material storage, reaction processes, pipeline transportation, and waste gas treatment. Building a reliable online gas monitoring system has become an engineering necessity to meet the requirements of GB/T 50493, AQ/T 9006, and SIL functional safety.

The Nexisense electrochemical sensor series targets industrial toxic gas and oxygen monitoring, providing low-power, high-selectivity, and long-term stability solutions. Through three-electrode/four-electrode design and modular output, it supports deployment from single-point fixed installation to plant-wide grid monitoring, seamlessly connecting with DCS/PLC/SCADA to achieve real-time concentration acquisition, threshold alarming, and interlock control.

Typical Gas Monitoring Application Scenarios in the Chemical Industry

Common monitoring targets in chemical parks and process units include CO, H₂S, NH₃, Cl₂, SO₂, PH₃, NO₂, and O₂. Fixed electrochemical detectors are deployed at high-risk locations such as reactor areas, storage tank bunds, pump rooms, sumps, loading/unloading stations, and wastewater treatment stations.

Within process units, sensors are arranged 0.5-1.5 m downwind of leakage sources to form a concentration field grid, achieving ppm-level continuous monitoring and leak source localization. Combined with wind direction and speed data, it supports diffusion simulation and emergency response.

Oxygen monitoring is applied in nitrogen blanketing, inerting, and confined spaces to ensure O₂ concentration remains within 19.5-23.5% vol, preventing fire/explosion risks caused by oxygen deficiency or enrichment.

After system integration, data preprocessing is performed via edge gateways. Exceeding thresholds (e.g., H₂S >10 ppm) triggers multi-level alarms, forced ventilation, feed cutoff, or ESD interlock, forming a layered defense mechanism.

Working Principle of Electrochemical Sensors and Advantages of Nexisense Series

Electrochemical sensors are based on a three-electrode (working electrode, reference electrode, counter electrode) or four-electrode (with auxiliary electrode) structure. The target gas undergoes oxidation/reduction at the working electrode, generating a microcurrent signal proportional to concentration, which is amplified via transimpedance and converted by A/D.

The Nexisense series includes:

• Three-electrode ME3 series: suitable for conventional industrial sites, lifetime >2 years, wide linear range, resolution up to 0.1 ppm.

• Four-electrode ME4 series: targeted at complex background gas interference scenarios, offering higher selectivity and poisoning resistance.

• Module series: integrated calibration circuit, signal conditioning, and RS485/4-20mA output, plug-and-play.

Core advantages:

• Low power consumption: typical<1 mW, suitable for long-term online and wireless deployment.

• High selectivity: cross-interference<5%, optimized electrolyte and catalyst for specific gases.

• Fast response: T90<30 s, supports real-time trend judgment.

• Stability: zero drift

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Compared to catalytic combustion or infrared sensors, electrochemical sensors offer higher accuracy in the ppb-ppm range for toxic gases, particularly suitable for chemical toxic gas monitoring.

Sensor Selection Guide and System Integration Considerations

Selection matches gas type and site conditions:

• Target gas: dedicated three/four-electrode for CO/H₂S/NH₃/Cl₂/SO₂/PH₃/NO₂; prioritize electrochemical oxygen sensor for O₂ (0-30% vol).

• Range and resolution: process areas prioritize 0-100/500 ppm, plant boundaries 0-10/50 ppm; resolution ≤1% FS.

• Environmental adaptability: operating temperature -20~50℃, built-in temperature/humidity compensation; explosion-proof Ex d IIC T6/Ex ia.

• Output form: modules prioritize RS485 Modbus RTU/TCP for easy networking.

Integration considerations:

• Unified communication protocol: 4-20mA, RS485 Modbus, HART, ensuring compatibility with existing control systems.

• Installation specification: sensors placed downwind of leakage source, avoid dead zones; protective cover against rain and dust, sampling point height per specification.

• Redundancy design: high-risk points use dual-sensor configuration, automatic fault switching and self-diagnosis.

• Calibration cycle: recommend 6-month field standard gas calibration (zero/span), record drift trends; use NIST-traceable standard gas.

• Data processing: access edge computing or cloud platform to achieve concentration heat maps, historical trends, and anomaly diagnosis.

Nexisense sensors have passed third-party explosion-proof/EMC certification, are compatible with mainstream protocols, and shorten integration and commissioning time.

Project Application Cases

A large fine chemical park deployed the Nexisense electrochemical grid system, covering over 30 monitoring points including chlorination workshops, ammonia areas, and storage tank zones. The system was integrated into the existing DCS, achieving real-time multi-gas monitoring of H₂S/Cl₂/CO and automatic ventilation interlock for exceedances. After commissioning, leak response time was shortened to<1 min, no poisoning incidents occurred, and annual maintenance costs were significantly reduced.

In another petrochemical unit renovation project, Nexisense oxygen and hydrogen sulfide sensors were embedded in the central control system and linked with ESD. Abnormal O₂ concentration triggers nitrogen blanketing replenishment, and H₂S exceedance directly cuts off feed. The project meets SIL2 requirements, enhancing the inherent safety level of the unit.

These applications validate the reliability and cost-effectiveness of electrochemical sensors in continuous chemical monitoring.

Nexisense OEM/Customization and Bulk Supply Advantages

Nexisense supports OEM labeling and customized development:

• Sensor housing/interface/range customization to match specific detectors or analyzers.

• Protocol extension: OPC UA, wireless LoRa/4G transmission.

• Bulk supply lead time<8 weeks, stable supply chain.

• Provides complete technical documentation, SDK, calibration guidance, and on-site support, reducing engineering workload for integrators.

Suitable for standardized procurement by gas detector manufacturers, EPC contractors, and chemical groups.

Frequently Asked Questions (FAQ)

1. How is cross-interference controlled for electrochemical sensors in high-humidity chemical environments?
      Nexisense uses dedicated filter membranes and built-in temperature/humidity compensation algorithms; at 90% relative humidity, cross-interference<5%, indication error maintained within ±10%.

2. What specific improvements does the four-electrode ME4 series offer over three-electrode in poisoning resistance?
      Additional auxiliary electrode compensates background current and electrolyte consumption; four-electrode sensors extend lifetime by 30-50% under organic solvents or high-concentration interference, with zero drift reduced by approximately 40%.

3. How is data integrity and real-time performance ensured for Modbus RTU communication during system integration?
      Supports CRC check and timeout retransmission, polling cycle<1 s; critical alarms use priority interrupt, ensuring response delay <200 ms.

4. How is sensor installation position optimized based on leakage source and wind field?
      Referencing GB/T 50493, 0.5-1.5 m downwind, combined with CFD simulation and wind rose diagram, avoiding vortex zones and dead corners to ensure coverage of main diffusion paths.

5. How are zero/span drift monitored and corrected during long-term operation?
      Perform two-point calibration with standard gas every 6 months, record drift trends; modules support automatic zero tracking, triggering maintenance alarm when drift exceeds ±5%.

6. How do sensors and wiring meet safety requirements in Ex d explosion-proof zones?
      Nexisense complies with Ex d IIC T6 Gb, cables use shielded twisted pair with grounding to prevent electromagnetic interference; junction boxes require same-grade explosion-proof to prevent spark escape.

7. What calibration and spare parts support does Nexisense provide during bulk procurement?
      Provides 3-5 year spare parts inventory commitment, on-site/mail calibration services, and annual maintenance contracts to ensure uninterrupted continuous operation.

8. What key regulatory indicators must the electrochemical gas monitoring system meet during project acceptance?
      Compliant with GB/T 50493 (design specification for toxic/combustible gas detection and alarming), AQ/T 9006 (safety instrumented system for chemical enterprises), SIL2 functional safety; Nexisense provides third-party certification reports and performance test data.

Conclusion

Chemical industry gas safety monitoring is evolving toward intelligence, grid-based, and predictive directions. Electrochemical sensors, with their low power consumption, high selectivity, and long-term stability, have become the mainstream technology for online monitoring of toxic gases and oxygen. Nexisense, through engineered integration solutions, provides reliable support from sensors to complete early warning systems, helping enterprises build proactive risk prevention mechanisms to meet increasingly stringent regulations and inherent safety requirements.

In the context of compressed project cycles and increased compliance pressure, selecting a partner with system compatibility and supply chain assurance will directly impact the lifecycle efficiency of monitoring systems and accident prevention capabilities.

If system integrators, instrument manufacturers, or chemical enterprises need to evaluate sensor configurations, verify prototypes, or discuss bulk solutions for specific units, welcome to contact the Nexisense technical team to jointly explore optimal deployment strategies.