Alphasense CL2-D4 Miniature Electrochemical Chlorine (Cl₂) Gas Sensor
| Brand | Alphasense |
|---|---|
| Origin | UK |
| Model | CL2-D4 |
| Sensitivity | −150 to −350 nA/ppm |
| Response Time (t₉₀) | <35 s |
| Linear Range | 0–10 ppm |
| Full-Scale Linearity Error | ±0.5 ppm |
| Overload Limit | 60 ppm |
| Resolution | <0.1 ppm |
| Dimensions | Ø14.5 × 8.3 mm |
| Expected Operational Life | 24 months |
| Storage Stability | 6 months |
| Operating Temperature | −20 to +50 °C |
| Operating Humidity | 15–90 % RH (non-condensing) |
| Load Resistance | 33 Ω |
Overview
The Alphasense CL2-D4 is a miniature, diffusion-controlled electrochemical gas sensor engineered for selective and stable detection of chlorine (Cl₂) in ambient air. Based on a three-electrode electrochemical cell architecture—comprising a working electrode (WE), counter electrode (CE), and reference electrode (RE)—the sensor operates via the controlled oxidation of Cl₂ at the catalytic WE surface, generating a current proportional to gas concentration. This amperometric principle ensures high specificity to chlorine while minimizing cross-sensitivity to common interferents such as NO₂, SO₂, and ozone under typical environmental conditions. The CL2-D4 is optimized for low-power, embedded applications where space constraints, long-term stability, and repeatable calibration intervals are critical—particularly in fixed gas detection systems, portable safety monitors, and process control instrumentation deployed in municipal water treatment, chemical manufacturing, and industrial hygiene environments.
Key Features
- Miniaturized cylindrical form factor (Ø14.5 × 8.3 mm) enabling integration into compact, battery-operated devices
- Stable baseline and low zero-current drift (<2 nA/month), supporting extended calibration intervals per ISO 12032 and IEC 60079-29-1 guidelines
- Linear output over 0–10 ppm Cl₂ with full-scale linearity error ≤±0.5 ppm, validated per EN 45544-2 test protocols
- Fast t₉₀ response time <35 seconds across the operating temperature range (−20 to +50 °C)
- Optimized electrolyte formulation providing consistent performance at 15–90 % RH (non-condensing)
- Integrated PTFE hydrophobic membrane preventing liquid ingress and particulate fouling
- Rated operational life of 24 months when operated within specified environmental limits; storage stability up to 6 months at 20 °C and <60 % RH
Sample Compatibility & Compliance
The CL2-D4 is designed for direct sampling of ambient or extracted air streams containing chlorine gas at trace to low-concentration levels (sub-ppm to 10 ppm). It is incompatible with reducing atmospheres containing high concentrations of H₂S or NH₃, which may temporarily suppress response or accelerate electrode poisoning. The sensor complies with key international standards for electrochemical gas sensors, including EN 45544-2 (performance requirements for toxic gas detectors), IEC 60079-29-1 (explosive atmospheres – gas detectors), and meets RoHS 2011/65/EU material restrictions. While not intrinsically safe by itself, it is routinely integrated into ATEX- and IECEx-certified transmitters when paired with appropriate barrier circuits and housing designs.
Software & Data Management
As a raw analog current-output device (typically −150 to −350 nA/ppm), the CL2-D4 requires external signal conditioning—including precision low-noise amplification, temperature compensation (via integrated NTC thermistor), and analog-to-digital conversion—to yield calibrated concentration values. Alphasense provides comprehensive technical documentation, including linearization coefficients, temperature compensation algorithms, and recommended filter time constants for digital firmware implementation. When deployed in regulated environments (e.g., drinking water facilities subject to EPA Method 301 or EU Directive 2000/60/EC), the sensor supports audit-ready data logging when interfaced with controllers compliant with FDA 21 CFR Part 11 (electronic records/signatures) and GLP/GMP data integrity requirements.
Applications
- Continuous chlorine monitoring in potable water disinfection systems and wastewater effluent channels
- Leak detection and area monitoring in chlorine storage, dosing, and handling facilities
- Personal and portable gas detectors for occupational health and safety (OEL compliance with OSHA PEL = 0.5 ppm, TLV-TWA = 0.4 ppm)
- Process control feedback loops in pulp & paper bleaching, pharmaceutical synthesis, and semiconductor etching lines
- Environmental air quality stations measuring industrial fence-line emissions near chlor-alkali plants
FAQ
What is the recommended load resistance for the CL2-D4?
The sensor is optimized for a 33 Ω load resistor to ensure proper biasing and maximize signal-to-noise ratio during current-to-voltage conversion.
Does the CL2-D4 require external temperature compensation?
Yes—while an integrated NTC thermistor is provided, accurate concentration reporting requires firmware-based temperature compensation using Alphasense’s published polynomial coefficients.
Can the CL2-D4 be exposed to condensing humidity?
No—operation outside the 15–90 % RH non-condensing range may cause electrolyte dilution or membrane saturation, leading to irreversible sensitivity loss.
Is factory calibration traceable to national standards?
Each CL2-D4 is individually tested against NIST-traceable chlorine gas standards at 2 ppm and 5 ppm; calibration certificates are available upon request.
How should the sensor be stored prior to installation?
Store upright in original sealed packaging at 20 °C and <60 % RH for no longer than 6 months; avoid freezing or exposure to solvents or ozone-rich environments.
