Space-saving, 2-gas Sensors for Industrial Safety and Process Monitoring
Alphasense Dual Toxic Gas Sensors combine two independent electrochemical channels in a single compact package to reduce instrument footprint, simplify multi-gas designs, and support next-generation portable, wearable, and fixed safety monitors. This family includes CO + H2S and SO2 + H2S combinations, providing fast response, proven stability, and long operational life across industrial safety, portable gas detection, and process monitoring applications. They are designed for applications where CO or SO2 must be monitored alongside H2S, providing reliable discrimination of gases with overlapping industrial sources.
Sensor Portfolio Overview
The Alphasense dual-gas portfolio includes four primary models, available across the mechanical formats OEMs rely on for portable and miniature devices.
Portable Industrial Safety Monitors – A-Series 2-Gas Sensors
Full-height, robust sensors for 4-gas and 5-gas personal safety instruments used in oil & gas, chemical plants, wastewater, and general industrial monitoring.- COH-A2: Dual CO (0–1000 ppm) + H2S (0–100 ppm) sensor
- SOH-A2: Dual SO₂ (0–20 ppm) + H2S (0–100 ppm) sensor
Miniature Wearables & Clip-on Devices – D-Series and H-Series 2-Gas Sensors
Low-profile sensors designed for badge-style wearables and compact personal monitors where footprint and height are highly constrained.- COH-D2: Miniature dual CO + H2S sensor with high-capacity filtering for cross-sensitivity control
- COH-H2: Dual CO + H2S sensor using the same electrochemical platform as COH-D2,adapted to the H-Series mechanical footprint
Choosing the right 2-gas sensor by application
General Industrial Safety (Portable Multi-Gas Instruments)
Ideal for applications where workers may be exposed to both CO or SO2 plus H2S in oil &gas, wastewater, chemical processing, confined spaces, and emergency response.
- COH-A2 (A-Series): Best choice for standard 4- or 5-gas portables needing stable CO + H2S detection with reduced hydrogen interference.
- SOH-A2 (A-Series): Recommended for sites with corrosive sulphur sources, enabling SO₂ and H2S discrimination for asset protection and worker safety.
Space-Constrained, Clip-on, and Wearable Devices
Used in personal exposure badges, small format detectors, and lightweight wearable monitors.- COH-D2 (D-Series): Optimized for miniature instruments; high-capacity filtration eliminates H2S cross-sensitivity to CO, ensuring long-term field stability.
High-Volume, Compact OEM Platforms
Ideal for global portable platforms where mechanical compatibility and cost structure are critical.- COH-H2 (H-Series): Delivers COH-D2 performance in a Honeywell-format, enabling drop-in compatibility for high-volume OEM devices.
Key Benefits Across the 2-Gas Sensor Portfolio
Two gases in one footprint — reduces instrument size, weight, and BOM cost. Ideal when board space is limited.Independent electrochemical channels ensure accurate, stable readings for each gas even in mixed-gas environments.
Fast T90 response supports rapid alarm activation for worker safety.
High-capacity filtration & low cross-sensitivity designs derived from the CO and H2S sensor families.
Multiple mechanical formats (A, D, H) support portable, compact, and high-volume instrument architectures.
Shared electrochemical platforms with single-gas CO, H2S, and SO2 sensors enable predictable performance and simplified OEM engineering.
Optional IST versions (COH-A2-IST, SOH-A2-IST) provide digital output and calibration memory for plug-and-play integration.
Why OEMs Choose Alphasense
Alphasense sensors are widely adopted by instrument manufacturers because they offer:
- Reliable batch-to-batch consistency, essential for multi-gas instruments with tight factory calibration tolerances.
- Decades of field-proven electrochemical platforms, deployed globally across industrial safety and environmental monitoring markets.
- Long operational life and low drift, reducing maintenance and recalibration costs.
- Robust technical support, including application guidance, cross-sensitivity data, and integration best practices.
- Optional Integrated Smart Technology (IST) for digital output, onboard calibration memory, and simplified temperature compensation.
How Dual Gas Sensors Work
Dual gas sensors use two independent electrochemical cells within a single housing. Each cell contains its own working, reference, and counter electrodes, ensuring that the gas reactions do not interfere with each other.
Electrochemical Detection
- The working electrode oxidizes or reduces the target gas.
- The current produced is proportional to the gas concentration.
- An external potentiostat maintains electrode bias and measures the resulting signal.
- CO channels often include specialized filters to suppress H₂S interference (e.g., in COH-A2, COH-D2, COH-H2).
- H2S channels include electrode formulations and internal filters that reduce interference from CO, SO2, NO2, and other species.
- High-capacity filters in the CO path prevent false CO readings caused by H₂S.
- SO2 + H2S dual designs (SOH-A2) allow clear discrimination between two corrosive sulphur gases that often co-occur in industry.
Why Measure CO or SO2 with H2S Gas?
CO + H₂S
Industries such as oil & gas, mining, steel production, wastewater, and confined spaces frequently generate both CO and H2S from combustion processes, engine exhaust, anaerobic decay, and hydrocarbon cracking. Monitoring both:
- Protects workers against two acutely toxic gases with different exposure profiles.
- Simplifies 4-gas and 5-gas instrument design by combining two essential toxic channels.
Refineries, pulp & paper plants, wastewater facilities, and biogas systems often contain corrosive sulphur gases such as SO2, alongside toxic H2S. Measuring both:
- Provides corrosion risk insight for equipment, piping, and sensors.
- Helps distinguish SO2 (oxidized sulphur) from H2S (reduced sulphur), which informs process control and maintenance.
- Enables dual protection for workers and critical assets.