| 1 | Catalytic Bead Combustible Gas Tester | Catalytic oxidation increases the temperature of a heated bead, changing its electrical resistance. | Methane, propane, butane, hydrogen and other combustible gases or vapors. | Usually 0–100% LEL; some instruments offer a low-range percentage-volume display. | Mining, utilities, oil and gas, confined-space entry, industrial maintenance and leak surveys. | Broad combustible-gas response; established technology; suitable for personal safety monitoring. | Requires oxygen for combustion; catalyst can be poisoned by silicones, sulfur compounds or lead; gas response varies by substance. | Confirm the target-gas calibration, LEL reference values, hazardous-area approval, sensor-poisoning resistance, alarm settings and calibration-gas availability. |
| 2 | Electrochemical Gas Tester | A target gas produces an electrochemical reaction that generates a current proportional to concentration. | Oxygen, carbon monoxide, hydrogen sulfide, sulfur dioxide, chlorine, ammonia, nitrogen dioxide and other toxic gases. | Commonly ppm-level for toxic gases; oxygen sensors are often approximately 0–25% volume. | Personal monitors, workplace exposure assessment, wastewater treatment, chemical processing and emergency response. | Good sensitivity at low concentrations; low power consumption; compact and relatively economical. | Finite sensor life; cross-sensitivity, temperature effects and drying or contamination may affect accuracy. | Check sensor replacement intervals, cross-interference data, expected humidity and temperature, bump-test procedure, alarm standards and local occupational-exposure requirements. |
| 3 | Non-Dispersive Infrared (NDIR) Gas Tester | The instrument measures infrared absorption at characteristic wavelengths of the target gas. | Carbon dioxide, methane, propane, refrigerants and selected hydrocarbons. | Ranges vary widely, from ppm-level instruments to percentage-volume process analyzers. | Combustible-gas monitoring, emissions checks, greenhouse-gas measurement, fermentation and process control. | No oxygen requirement; long sensor life; generally resistant to catalyst poisons; good repeatability. | Water vapor, dust, pressure changes and overlapping absorption can influence readings; not every gas absorbs infrared radiation strongly. | Review target-gas selectivity, pressure and humidity compensation, response time, measurement uncertainty, sampling configuration and required emissions methodology. |
| 4 | Photoionization Detector (PID) Gas Tester | An ultraviolet lamp ionizes compounds with ionization potentials below the lamp energy; the resulting current is measured. | Volatile organic compounds such as solvents, fuels and aromatic hydrocarbons. | Common portable ranges are from sub-ppm levels to hundreds or thousands of ppm, depending on configuration. | Industrial hygiene, environmental surveys, spill response, tank entry and soil or vapor screening. | High sensitivity and fast response for many VOCs; useful for locating changing concentration zones. | Does not identify individual compounds without additional analysis; humidity and lamp contamination can affect readings; some VOCs are not ionized by the selected lamp. | Select the ultraviolet lamp energy, correction-factor library, lamp-cleaning method, humidity tolerance, calibration gas and occupational-exposure reporting capability. |
| 5 | Metal-Oxide Semiconductor (MOS) Gas Tester | Adsorption of gas on a heated semiconductor surface changes its electrical resistance. | Combustible gases, VOCs, carbon monoxide and selected industrial gases, depending on the sensing material. | Often designed for broad relative detection rather than precise compound-specific measurement; ranges are sensor-dependent. | Low-cost alarms, indoor-air monitoring, appliance checks and preliminary leak indication. | Low purchase cost; durable sensing element; can respond to a wide range of gases. | Limited selectivity; strong humidity, temperature and background-gas effects; typically less suitable for regulatory quantitative measurements. | Verify whether the instrument provides concentration data or only an alarm index, and request repeatability, drift, environmental compensation and calibration documentation. |
| 6 | Thermal Conductivity Gas Tester | The change in thermal conductivity of a gas mixture alters heat transfer from a heated element. | Hydrogen, helium, carbon dioxide, methane and binary or high-concentration gas mixtures. | Often percentage-volume or high-concentration ranges; exact performance depends on the background gas. | Gas blending, inerting, hydrogen systems, industrial furnaces and process monitoring. | No oxygen requirement; can measure gases that are difficult for electrochemical sensors; suitable for high concentrations. | Poor selectivity in complex mixtures; pressure, flow and temperature changes can cause errors. | Confirm the background-gas composition, calibration method, sample pressure and flow requirements, allowable ambient conditions and suitability for hazardous locations. |
| 7 | Paramagnetic Oxygen Analyzer | Oxygen is attracted into a magnetic field, and the resulting force or movement is measured. | Oxygen in process gases, combustion systems, medical-gas production and laboratory applications. | Commonly percentage-volume oxygen ranges, including low-percentage and near-atmospheric measurements. | Continuous process analysis, combustion optimization, inerting verification and gas-quality control. | Good selectivity for oxygen; no consumable electrochemical cell; suitable for continuous measurement. | Usually more sensitive to vibration, installation quality and sample conditioning than simple portable sensors. | Evaluate sample filtration and drying, pressure regulation, response time, vibration conditions, calibration gases and continuous-monitoring compliance requirements. |
| 8 | Zirconia Oxygen Analyzer | A heated zirconium-oxide electrolyte generates a voltage related to the oxygen partial-pressure difference. | Oxygen in flue gas, combustion exhaust, furnaces and industrial process streams. | Commonly used from low oxygen concentrations to percentage-volume oxygen, depending on the probe and design. | Boiler and furnace control, combustion-efficiency monitoring and oxygen-deficiency measurement in process gas. | Fast response; suitable for hot gas measurement; does not require a reference-gas cylinder in many designs. | Requires high operating temperature; combustible gases in certain oxygen-rich conditions can affect readings; dust and corrosive components may damage the probe. | Check probe temperature, insertion length, flue-gas dust and acid-dew-point conditions, maintenance access, calibration procedure and replacement-probe cost. |
| 9 | Tunable Diode Laser Absorption (TDLAS) Gas Tester | A tunable laser scans a gas-specific absorption line and calculates concentration from the absorbed light. | Methane, hydrogen sulfide, ammonia, water vapor, carbon monoxide and other gases with suitable absorption lines. | Application-specific ranges from trace levels to percentage-volume concentrations. | Open-path leak detection, pipeline inspection, emissions monitoring and demanding process applications. | High selectivity; fast response; can measure remotely or across long optical paths; minimal contact with the sample. | Higher purchase cost; optical alignment, dust, rain, fog and line-of-sight obstructions can reduce performance. | Assess open-path distance, weather protection, optical-path availability, hazardous-area certification, data logging, false-alarm behavior and local service capability. |
| 10 | Ultrasonic Gas Leak Detector | Detects high-frequency airborne sound generated by pressurized-gas leakage rather than measuring gas concentration directly. | Pressurized air, natural gas, hydrogen and other compressed gases that create detectable ultrasonic emissions. | Reported as sound level or leak indication; it does not normally provide ppm or percentage-volume concentration. | Compressed-air audits, process plants, gas-cylinder systems and outdoor leak detection. | Fast response; works without gas sampling; useful in windy or ventilated areas where gas-cloud detection is difficult. | Needs sufficient pressure differential; background ultrasonic noise can interfere; cannot confirm toxic exposure or oxygen deficiency. | Use it as a leak-location tool rather than a personal exposure monitor, and compare detection distance, minimum leak rate, noise filtering, weather resistance and hazardous-area approvals. |
