Alphasense gas sensors

Technical selection of Alphasense gas sensors: O2-A2, O2-A3, O2-G2 oxygen sensors, CH-A3 methane pellistors, SO2-AF and CO-AF toxic sensors, PID detectors, NDIR sensors and 4–20 mA boards.

Galvanic oxygen sensors O2-A2, O2-A3, O2-G2

Alphasense O2-A2, O2-A3 and O2-G2 galvanic sensors measure 0–30% O2 with no bias voltage and a 2-pin interface. O2-A2 and O2-G2 are rated for 24 months, O2-A3 for 36 months. The G-Series half-height package suits wearable and compact instruments.

Range 0–30% O2
O2-A2 T90 under 8 s
O2-A3 lifetime 36 months
Operates from −30 to +55 °C

Catalytic pellistors CH-A3 for methane

The CH-A3 A-Series catalytic pellistor is calibrated to methane over 0–100% LEL and also responds to other hydrocarbons. Sensitivity is 15–22 mV per % CH4 with T90 under 15 s. It is designed for Ex d flameproof housings and an operating life over 24 months.

Range 0–100% LEL methane
Sensitivity 15–22 mV per % CH4
T90 under 15 s
Operating life over 24 months

Electrochemical toxic gas sensors CO-AF, SO2-AF, NH3-B1

Alphasense CO-AF, SO2-AF and NH3-B1 electrochemical sensors serve portable and fixed gas detectors. CO-AF covers 0–5,000 ppm with an internal filter against H2S, NO2, NO and SO2. SO2-AF covers 0–50 ppm, and NH3-B1 covers 0–100 ppm with a +200 mV bias.

CO-AF range 0–5,000 ppm
SO2-AF range 0–50 ppm
NH3-B1 bias +200 mV
SO2-AF T90 under 35 s

Four-electrode air quality sensors

NO2-B43F, H2S-A41 and CO-A4F sensors use a fourth electrode for baseline compensation and resolve gas at ppb level. NO2-B43F (B-Series) covers 0–20 ppm NO2, H2S-A41 covers 0–50 ppm and CO-A4F covers 0–500 ppm for air quality and fence-line monitors.

NO2-B43F range 0–20 ppm
H2S-A41 range 0–50 ppm
CO-A4F range 0–500 ppm
NO2-B43F T90 under 80 s

Photoionisation detectors PID-AH5

The PID-AH5 A-Series photoionisation detector measures volatile organic compounds over 0–40 ppm with a 3 ppb minimum detection level. Its 10.6 eV lamp is user-replaceable, and an on-board filter protects the ionisation chamber. It shares the 4-pin footprint of other A-Series PIDs.

VOC range 0–40 ppm
Minimum detection 3 ppb
Replaceable 10.6 eV UV lamp
Sensitivity 25–65 mV/ppm

NDIR sensors IRC-A1 for CO2 and IRM-AT for methane

The IRC-A1 pyroelectric NDIR sensor measures CO2 from 0–5,000 ppm up to 0–100% vol. The thermopile-based IRM-AT measures methane over 0–2.5% and 0–100% vol. Both reach T90 under 40 s at 20 °C; IRM-AT is mounted inside a suitable Ex-approved enclosure.

IRC-A1 CO2 up to 100% vol
IRM-AT CH4 range 0–2.5% vol
T90 under 40 s at 20 °C
IRC-A1 MTBF over 5 years

Optical particle counters OPC-N3

The OPC-N3 optical particle counter detects particles from 0.35 to 40 μm and sorts them into 24 size bins. It reports PM1, PM2.5 and PM10 mass concentrations at a 5.5 L/min total flow over an SPI interface. The laser is Class 1, and the operating range is −10 to +50 °C.

Particle size 0.35–40 μm
24 particle-size bins
Total flow 5.5 L/min
SPI interface, Class 1 laser

Transmitter boards 4–20 mA

Digital 4–20 mA boards work with all Alphasense toxic gas sensors; analogue boards suit most oxygen sensors and unbiased B-Series toxic sensors. The 2-wire loop output is linear from 4 mA at 0 ppm to 20 mA at the specified full scale. NDIR boards add a USB output.

4–20 mA current loop
2-wire loop connection
Typical 100 ohm load resistor
NDIR board: 4–20 mA and USB

Choosing an Alphasense sensor technology for the target gas

Alphasense manufactures gas sensors in several technologies: electrochemical cells for oxygen and toxic gases, catalytic pellistors for flammable gases, NDIR infrared sensors for CO2 and methane, PID detectors for volatile organic compounds, and optical particle counters.

Portable instruments typically use O2-A2 or the compact O2-G2 for oxygen, while O2-A3 offers a 36-month life for long deployments. Methane up to 100% LEL is measured by the CH-A3 pellistor, and volume concentrations up to 100% by the IRM-AT infrared sensor.

Sensors for portable and fixed gas detectors

The shared A-Series footprint lets one instrument combine oxygen, methane and toxic channels such as O2-A2, CH-A3, CO-AF and SO2-AF. The B-Series, with a larger electrolyte volume, targets fixed sites and humid environments, for example NH3-B1 in barns and greenhouses.

Four-electrode NO2-B43F, H2S-A41 and CO-A4F sensors resolve gas at ppb level and are used in air quality networks and fence-line monitoring around industrial sites.

Sensor integration: 4–20 mA boards and gas sampling

For fixed systems Alphasense offers digital and analogue 4–20 mA transmitter boards with a 2-wire loop; NDIR boards add a USB output. Boards supplied with sensors are pre-calibrated to the specified range.

In sampling systems the gas flows across the sensor face at about 0.5 L/min, the pump sits upstream of the sensor, and a particulate filter protects the inlet in dirty environments.

Alphasense and model names are trademarks of their respective owners and are used only to identify the equipment for which we source parts. SpareX is not an official dealer, distributor or representative of Alphasense and is not affiliated with the trademark owner. Origin, documents and warranty are stated for each item in the quotation.