Industrial Gas Detection: Choosing Sensors for CO, H₂S, H₂, and O₂

A practical guide for OEM designers building fixed, portable, and connected safety instruments

IN BRIEF  Choose the sensing element around the hazard, concentration range, response requirement, environment, and interfering gases—then validate the complete instrument under representative conditions.

Industrial plants rarely face a single gas risk. A wastewater facility may need to detect hydrogen sulfide around sludge handling, oxygen deficiency in confined spaces, carbon monoxide near combustion equipment, and hydrogen near electrolysis or energy systems. The challenge is not simply to “add a gas sensor.” It is to match each hazard with the right sensing channel and engineer the detector around it.

This guide examines four SensorsX electrochemical sensor families and the design decisions that turn a sensing element into a dependable monitoring instrument.

Why industrial gas monitoring is a multi-variable problem

Gas behavior, site conditions, and instrument architecture all affect detection performance. Four issues deserve attention early in the design cycle:

Multiple hazards. Toxic exposure, flammability, and oxygen displacement may coexist in the same facility. A multi-gas design is often more appropriate than a universal-sensor assumption.

Fast concentration changes. Leaks from valves, seals, pipelines, batteries, or process equipment can develop quickly. Sensor response must support the system-level alarm and mitigation timeline.

Cross-sensitivity. Electrochemical cells can respond to gases other than their target. Interference must be assessed against the actual process-gas mix, not only a laboratory table.

Environmental variation. Temperature, humidity, condensation, contamination, pressure, and airflow can shift baseline, sensitivity, or gas transport. Enclosure and compensation design matter.

Four SensorsX sensing options

The following product families cover common toxic-gas, flammable-gas, and oxygen-monitoring requirements. Values shown are the supplied standard specifications; confirm the exact ordering code and current datasheet before freezing a design.

Table 1. Standard configurations summarized from the supplied SensorsX product information. “Response” values are specification limits, not comparative test results.

Carbon monoxide: SX-GCOTSA

CO is produced by incomplete combustion and can accumulate around boilers, furnaces, generators, engine-test areas, garages, and enclosed industrial spaces.

The SX-GCOTSA is a three-electrode potentiostatic cell with a standard 0–1000 ppm range, 1 ppm resolution, and a specified response time below 25 seconds. The supplied data states a linear regression coefficient of R² = 0.999.

Typical integration targets

• Combustion-safety monitors
• Fixed and portable CO alarms
• Exhaust and ventilation controls

Hydrogen sulfide: SX-GH2STSA-320

H₂S is associated with wastewater and sludge processing, sewer systems, petroleum refining, pulp and paper, mining, and other sulfur-bearing processes.

With a standard 0–100 ppm range and high nominal sensitivity, the SX-GH2STSA-320 is suited to compact H₂S instruments where low-power continuous monitoring is required.

Typical integration targets

• Wastewater and sludge areas
• Sewer and underground infrastructure
• Petroleum, petrochemical, and mining sites

Hydrogen: SX-GH2TSA-2A0

Hydrogen may be present in electrolysis, chemical processing, battery production, energy systems, laboratories, storage, and gas-handling operations. Because it is highly flammable, accumulation in a poorly ventilated area requires prompt detection and control.

The SX-GH2TSA-2A0 provides a 0–1000 ppm standard range and a proportional electrical response for integration with signal conditioning, compensation, display, and alarm electronics.

Typical integration targets

• Electrolysis and hydrogen handling
• Battery and energy systems
• Chemical and metal-processing equipment

Oxygen: SX-GO2EGA-110

Oxygen monitoring addresses both deficiency and enrichment. Deficiency can occur when another gas displaces air or when oxygen is consumed; enrichment can increase combustion severity.

The two-electrode galvanic SX-GO2EGA-110 is self-powered at the cell level and covers 0–25% vol. Its specified output is 100 ± 20 µA at 20.9% oxygen, with 0.1% vol. resolution.

Typical integration targets

• Confined-space instruments
• Mining and petrochemical safety systems
• Oxygen-deficiency and air-quality monitors
  

Figure 1. Upper response-time limits from the supplied standard specifications. A lower limit can support a faster system response, but detector design, gas delivery, calibration, and alarm logic also affect end-to-end performance.

A five-step sensor-selection framework

1. Define the hazard — Identify the target gas and whether the primary concern is toxicity, flammability, oxygen deficiency, oxygen enrichment, or a combination.

2. Set the measurement envelope — Establish the expected background, normal operating range, alarm region, credible peak concentration, and required resolution.

3. Map the environment — Document temperature, humidity, condensation risk, pressure, airflow, dust, chemicals, and likely interfering gases.

4. Match the dynamics — Relate sensor response and recovery to gas transport, sampling path, firmware filtering, alarm delay, and the required protective action.

5. Plan validation and maintenance — Define calibration gas, bump-test approach, acceptance limits, replacement criteria, diagnostics, and service intervals for the complete instrument.

Integration: the sensor is one layer of the detector

An electrochemical cell typically produces a small current or voltage related to gas concentration. Reliable monitoring depends on how the rest of the instrument preserves, interprets, and acts on that signal.

Figure 2. The sensing cell, electronics, firmware, enclosure, calibration, and protective actions must be engineered and validated as one system.

Electronics and firmware

• Confirm sensor bias requirements and use a low-noise analog front end appropriate to the cell output.
• Budget for amplifier offset, leakage current, electromagnetic interference, ADC resolution, and power-supply noise.
• Implement temperature compensation, baseline management, range checks, open/short detection, and sensor end-of-life diagnostics where appropriate.
• Treat filtering and alarm persistence carefully: excessive smoothing can hide a rapid concentration rise.

Mechanical design and placement

The enclosure must allow representative gas diffusion while protecting the cell from water, condensation, dust, oils, paints, solvents, silicone-containing materials, adhesives, and prolonged corrosive exposure. Membranes, splash barriers, condensation control, suitable materials, and an engineered sampling path may be required.

Detector location should follow a facility risk assessment that considers leak sources, gas behavior, airflow, ventilation, equipment layout, access, and maintenance—not gas density alone. Candidate locations include valves, pumps, compressors, seals, process equipment, tanks, dosing rooms, battery rooms, combustion equipment, confined spaces, and exhaust paths.

Calibration, cross-sensitivity, and field validation

Calibrate with the actual target gas and an appropriate background gas. For positive-output electrochemical CO and H₂S cells, oxygen participates in the reaction, so calibration gas balanced in air is generally preferred when consistent with the product instructions. Apply gas at a stable, controlled flow compatible with the fixture and sensor datasheet; a concentrated jet can distort the result or damage the sensing element.

Cross-interference data describes typical laboratory behavior, not a universal correction factor. Validate the complete instrument under representative mixtures, temperatures, humidity, exposure history, and aging conditions. Establish production calibration and field maintenance around the performance of the finished detector—not the cell in isolation.

SAFETY NOTE  A sensor component does not by itself make a certified safety instrument. Alarm thresholds, functional safety, explosion protection, EMC, environmental qualification, installation, and maintenance must comply with the requirements applicable to the final product and site.

Example: a wastewater treatment monitoring strategy

A wastewater facility illustrates why multi-gas architecture matters. A practical risk-based design might combine:

• H₂S channels around sludge handling, anaerobic treatment, wet wells, and sewer-gas pathways.
• O₂ channels for confined-space entry and areas where gases can displace air.
• CO channels near boilers, generators, furnaces, or other combustion sources.
• H₂ channels only where electrolysis, battery, chemical, or energy processes create a credible hydrogen hazard.

The connected control system can then support local audible/visual alarms, remote notification, ventilation control, interlocked shutdown, event logging, centralized monitoring, and maintenance records. Alarm thresholds and actions should be established from the process risk assessment and applicable regulations or standards.

Key takeaways for OEM teams

• Select by hazard and application conditions—not by gas name alone.
• Use separate sensing channels when toxic, flammable, and oxygen-related risks coexist.
• Compare response specifications in the context of the full detector response chain.
• Design the analog front end, enclosure, sampling path, compensation, diagnostics, and alarm logic around the chosen cell.
• Validate cross-sensitivity, calibration, environmental performance, and maintenance on the finished instrument.

Talk to SensorsX about your application

To identify a suitable configuration, share the target gas, measuring range, operating environment, potential interfering gases, instrument architecture, certification context, and expected annual volume. SensorsX can help evaluate the SX-GCOTSA, SX-GH2STSA, SX-GH2TSA, and SX-GO2EGA families for your detector design.