Chlorine Gas Sensors
Select Cl₂ sensors for portable safety, fixed industrial detection, water-treatment chlorine rooms, chemical facilities and environmental monitoring. Compare electrochemical cells, modules, response time, humidity behavior and reactive-gas sampling requirements.
Chlorine gas in air is not residual chlorine in water
The word “chlorine sensor” is used for two different measurements. Gas Nose treats this page as an airborne Cl₂ gas-sensor page because it sits inside the gas-sensor library.
| Measurement | Target | Typical unit | Sensor format | Typical application |
|---|---|---|---|---|
| Chlorine gas | Cl₂ in air / process gas | ppm | Electrochemical gas cell or module | Industrial safety, chlorine rooms, chemical plants, ambient monitoring |
| Residual chlorine in water | Free / residual chlorine in solution | mg/L | Water-quality probe or module | Water works, pools, wastewater, disinfection control |
Airborne Cl₂ sensor
The sensing face stays in the gas phase. The design is built around gas diffusion, ppm response, enclosure flow and toxic-gas alarm behavior.
Residual-chlorine water sensor
The sensing interface is designed for liquid contact. Measurement chemistry, units, calibration and maintenance are different from a Cl₂ gas cell.
Choose the chlorine sensor around the hazard and sampling method
Most dedicated Cl₂ safety sensors use electrochemical technology, so selection usually comes down to package size, range, T90, environmental stability, sampling arrangement and interference behavior.
0–20 ppm class
Compact electrochemical cells are used for industrial hygiene, confined-space and emergency-response instruments.
- Fast T90
- Miniature package and low noise
0–20 ppm class
Larger cells can provide more electrolyte volume and stronger environmental stability for fixed transmitters.
- Humidity tolerance
- Long-term baseline stability
Airborne leak detection
The gas sensor monitors Cl₂ released into the room or ventilation path. It does not measure disinfectant residual in the water stream.
- Place near credible release zones
- Account for airflow
10–50 ppm class
Fixed detection may need a wider range or stronger overload tolerance where process releases can exceed personal-monitor concentrations.
- Review maximum exposure
- Check corrosive environment
Low ppm
Stable zero, low-noise electronics and controlled humidity become more important when monitoring below alarm-level concentrations.
- High sensitivity
- Temperature/humidity compensation
Pumped system
Pumps can move the sensing point away from the sensor, but tubing and fittings create Cl₂ loss and delay.
- Use compatible materials
- Keep the path short
How electrochemical chlorine sensors work
Dedicated Cl₂ gas sensors are commonly amperometric electrochemical cells. Chlorine diffuses to the working electrode and participates in a reduction reaction. The resulting current is proportional to gas concentration over the sensor's specified linear range.
Working electrode
Chlorine reacts at the sensing electrode and generates the measurement current.
Controls sensitivity and target-gas response.Reference electrode
Keeps the working-electrode potential stable so the cell can operate at the intended electrochemical condition.
Common in 3-electrode Cl₂ cells.Diffusion path
Controls how Cl₂ reaches the catalyst. Filters, membranes and enclosure openings directly affect system response.
Critical for reactive gas.Signal electronics
The sensor current is converted to voltage or digital concentration by the analog front end and calibration algorithm.
Modules can integrate this stage.Chlorine gas sensors for different OEM requirements
The products below cover compact portable, fixed high-humidity, standard industrial, wider-range and conditioned-module routes. Compare them within the application they are designed to serve.
| OEM need | Manufacturer | Model | Type | Published range | Key engineering point | Official source |
|---|---|---|---|---|---|---|
| Standard industrial Cl₂ cell | Winsen | ME4-Cl₂ | Electrochemical | 0–20 ppm | 32 mm package, 0.1 ppm resolution, T90 ≤60 s, 2-year published life; chemical, pharmaceutical and environmental applications. | Official ↗ |
| Smaller industrial Cl₂ cell | Winsen | ME3-Cl₂ | Electrochemical | 0–10 ppm | 0.1 ppm resolution, T90 <60 s, 2-year published life; designed for industrial and environmental detection. | Official ↗ |
| Portable / fixed safety | Alphasense | CL2-A1 | A-Series electrochemical | 0–20 ppm | High output sensitivity, T90 <60 s and 24-month warranted life for industrial hygiene and water-treatment safety. | Official ↗ |
| Miniature personal monitor | Alphasense | CL2-D4 | D-Series electrochemical | 0–20 ppm | Miniature package, T90 <35 s, designed for clip-on and lightweight portable instruments. | Official ↗ |
| Fixed / high-humidity installation | Alphasense | CL2-B1 | B-Series electrochemical | 0–20 ppm | Larger electrolyte volume, high sensitivity and fixed-installation positioning for humid water-treatment and scrubber environments. | Official ↗ |
| Fast portable / fixed integration | SENKO | SS2168 | Electrochemical | 0–20 ppm max overload 50 ppm | T90 <30 s, <0.1 ppm typical resolution and >24-month operating life in air. | Official ↗ |
| Low-range Sensoric route | Honeywell | Cl2 3E 10 | 3-electrode electrochemical | 0–10 ppm | <0.05 ppm published resolution, T90 <60 s and applications including water-treatment plants, pools and chemical industry. | Datasheet ↗ |
| Wider-range Sensoric route | Honeywell | Cl2 3E 50 | 3-electrode electrochemical | 0–50 ppm | Higher dynamic range, <0.05 ppm published resolution and >24-month life expectancy in air. | Datasheet ↗ |
| Conditioned OEM module | Winsen | ZE03-Cl₂ configuration | Electrochemical module | Gas-specific manual | UART + analog voltage output, DC 5 V, <5 mA; Cl₂ is listed among the supported gases. | Official ↗ |
| Extended-range Cl₂ | Membrapor | Cl2/C family | Compact electrochemical | 20 / 200 / 2,000 / 5,000 ppm classes | Multiple range options allow the sensor range to be matched to safety or process concentration instead of overloading a low-range cell. | Official ↗ |
Manufacturer ranges are component specifications. Confirm the latest datasheet, cross-sensitivity, gas-delivery method and finished detector requirements before design freeze.
Chlorine sensor priorities change with the installation
Portable worker-safety instruments
For personal exposure monitoring, compact size and alarm response usually matter more than a wide process range.
| Model | Range | T90 | Engineering point |
|---|---|---|---|
| Alphasense CL2-D4 | 0–20 ppm | <35 s | Miniature clip-on route with a small D-Series footprint. |
| SENKO SS2168 | 0–20 ppm | <30 s | Fast standard electrochemical route with published low cross-sensitivity to several reducing gases. |
| Alphasense CL2-A1 | 0–20 ppm | <60 s | Standard A-Series package for portable and fixed industrial hygiene instruments. |
Fixed chlorine rooms and water-treatment plants
These systems monitor chlorine released into room air from cylinders, dosing systems, valves or process equipment. High humidity, ventilation and corrosion affect the installation.
| Route | Range | Why it fits | Design check |
|---|---|---|---|
| Alphasense CL2-B1 | 0–20 ppm | Larger fixed-installation package and high-humidity positioning. | Condensation, splash protection and room airflow. |
| Winsen ME4-Cl₂ | 0–20 ppm | 32 mm industrial electrochemical cell with 0.1 ppm resolution. | Use non-condensing enclosure and validate the gas path. |
| Honeywell Cl2 3E 10 | 0–10 ppm | Low-range Sensoric cell with water-treatment application history. | NO₂ / O₃ / ClO₂ cross-response and detector calibration. |
Chemical and process facilities
Process areas can see concentrations beyond a personal-monitor full scale. Wider-range sensors help avoid saturation where the instrument needs to follow a larger release.
| Model / family | Range class | Engineering point | Official source |
|---|---|---|---|
| Honeywell Cl2 3E 50 | 0–50 ppm | Higher dynamic range while retaining sub-0.1 ppm sensor resolution. | Datasheet ↗ |
| Membrapor Cl2/C-200 | 200 ppm | Wider process range in compact electrochemical format. | Official ↗ |
| Membrapor Cl2/C-2000 | 2,000 ppm | Extended range for high-concentration gas streams. | Official ↗ |
| Membrapor Cl2/C-5000 | 5,000 ppm | Very high-range route; compare against dedicated process analyzers where continuous accuracy is critical. | Official ↗ |
What usually causes chlorine gas measurement problems
Reactive-gas sampling loss
Cl₂ can be lost between the sampling point and the sensor. Surface chemistry, tubing length, filters, moisture and dead volume can all reduce or delay the delivered concentration.
- Keep pumped sample paths as short as practical.
- Use tubing, regulators and fittings suitable for chlorine service.
- Validate the complete gas path with target gas, not just the sensor on a bench.
Humidity and condensation
Many electrochemical Cl₂ cells specify operation at high relative humidity but explicitly exclude condensation. Water on filters or diffusion openings changes transport and can damage electronics.
- Use splash protection without blocking gas diffusion.
- Do not place the cell where washdown or condensate can collect on the inlet.
- For water-treatment rooms, review ventilation and wet-process sources together.
Oxidizing-gas interference
NO₂, ozone and chlorine dioxide can create positive readings on some chlorine electrochemical sensors. The exact response depends on electrode chemistry and filter design.
- Use the exact model cross-sensitivity table.
- Do not assume a Cl₂ sensor is a ClO₂ or O₃ sensor because it responds to them.
- Where multiple oxidants are present, use selective channels or a validated compensation strategy.
Corrosive installation
Chlorine leaks can attack connectors, electronics and enclosure materials even when the sensing cell itself survives the exposure.
- Select enclosure and connector materials for the actual plant environment.
- Keep electronics out of direct condensate and chemical splash zones.
- Inspect fixed detectors after significant chlorine releases.
Keep chlorine close to the sensor when possible
Diffusion detectors place the sensing element at the measurement point. Pumped systems move gas through tubing to a remote sensor. Both can work, but reactive-gas losses make pumped Cl₂ systems more demanding than a simple CO sample line.
Diffusion measurement
- Shortest gas path.
- No pump delay or sample-line adsorption.
- Good choice for room or area monitoring when the detector can be installed near the hazard.
- Enclosure diffusion and mounting location still need validation.
Pumped measurement
- Useful for ducts, remote points and inaccessible equipment spaces.
- Adds tubing residence time and surface loss.
- Needs chlorine-compatible wetted materials.
- Calibration gas should pass through the same sample path where practical.
Chlorine Cl₂ and chlorine dioxide ClO₂ need separate sensor decisions
Both are oxidizing disinfectant gases, but they are different compounds. A Cl₂ sensor may respond to ClO₂ as an interference, and a ClO₂ sensor may have its own response to chlorine. Select the sensor for the actual target gas.
| Target gas | Formula | Typical sensor | Design implication |
|---|---|---|---|
| Chlorine | Cl₂ | Cl₂ electrochemical gas sensor | This page covers this target. |
| Chlorine dioxide | ClO₂ | Dedicated ClO₂ electrochemical sensor | Use a ClO₂-specific sensor or validated multi-gas system. |
Winsen chlorine gas elements and module
Winsen's current chlorine gas offering is smaller than its CO or NH₃ range, but it does include raw electrochemical Cl₂ cells and a configurable toxic-gas module.
ME3-Cl₂
0–10 ppm measurement range, 100 ppm maximum detecting concentration, 0.1 ppm resolution, T90 <60 s and 2-year anticipated life.
ME4-Cl₂
0–20 ppm, 0.1 ppm resolution, T90 ≤60 s, -20 to 50°C and 15–90%RH non-condensing. Used in chemical, pharmaceutical and environmental detection.
ZE03-Cl₂ configuration
ZE03 supports Cl₂ among multiple toxic gases and provides UART plus analog voltage output. The gas-specific measurement range should be taken from the current configuration manual.
Residual chlorine requires a water-quality sensor
Winsen ZW-RCl101 and MW-RCl101 are water-quality products, not airborne Cl₂ gas sensors. They belong in residual-chlorine / water-treatment instrumentation rather than the gas-sensor shortlist above.
ZW-RCl101 module
- Measures residual chlorine in solution.
- 0.01 mg/L minimum graduation.
- RS485 output and <90 s published response.
- Applications include water works, medical wastewater and swimming pools.
MW-RCl101 probe
- Polarographic residual-chlorine water-quality sensor.
- 0–20 mg/L published range.
- 0.01 mg/L minimum graduation.
- Analog sensing element for water-quality OEM equipment.
Other chlorine gas sensor product ranges
These manufacturers publish Cl₂ electrochemical sensors for portable safety, fixed detection, water-treatment environments and process monitoring.
Alphasense
A-Series, B-Series and miniature D-Series chlorine sensors for portable and fixed instruments.
Honeywell Sensoric
3-electrode Cl₂ sensors including 10 ppm and 50 ppm range families.
SENKO
0–20 ppm electrochemical chlorine sensor for portable, fixed and ambient-air instruments.
Membrapor
Compact chlorine sensors from 20 ppm to multi-thousand-ppm process ranges.
Submit a Cl₂ sensor
Manufacturers can provide an official product page and current datasheet for inclusion.
Chlorine calibration must include the delivery system
Reactive-gas calibration can fail even when the cylinder concentration is correct. Regulators, tubing, fittings, filters and flow time determine how much Cl₂ reaches the sensing face.
Bump test
Confirms that chlorine reaches the detector and that the measurement/alarm chain responds.
Span calibration
Uses a known Cl₂ concentration to establish or adjust response. Follow the instrument-specific flow and stabilization procedure.
Post-release inspection
After a significant chlorine event, inspect filters, enclosure, connectors and response recovery before returning a detector to service.
Chlorine gas sensor questions
Does this page cover chlorine in air or chlorine in water?
This page covers airborne chlorine gas, Cl2, measured in ppm. Residual chlorine in water is a different measurement made with a water-quality probe or module and is typically expressed in mg/L.
What Cl₂ sensor range is common for industrial safety?
Many portable and fixed chlorine safety sensors are designed around 0–10 ppm or 0–20 ppm measurement ranges. Wider-range products are available for process or upset conditions. The final range should follow the alarm strategy and credible leak concentration.
Can a chlorine gas sensor be used to measure residual chlorine in water?
No. A standard Cl2 gas sensor measures chlorine reaching a gas diffusion path. Residual chlorine in water requires a water-quality sensor designed to contact the liquid, such as a polarographic or electrochemical residual-chlorine probe.
Why does sampling tubing matter for chlorine gas?
Chlorine is reactive and can be lost on tubing, wet surfaces, filters and fittings. Long sample lines can slow the response and reduce the concentration reaching the sensor. Diffusion measurement is often simpler when the detector can be placed near the monitored location.
Is chlorine gas the same as chlorine dioxide?
No. Cl2 and ClO2 are different target gases with different chemistry and sensor response. Some Cl2 sensors have cross-sensitivity to ClO2, but that does not make them interchangeable.
What cross-sensitivities should I check for a Cl₂ electrochemical sensor?
Check the exact sensor datasheet for gases expected at the site. Common oxidizing interferents include NO2, ozone and chlorine dioxide, while other gases may produce smaller positive or negative responses depending on the sensor chemistry and filter.
Should I use diffusion or pumped sampling for chlorine?
Use diffusion where the sensor can be mounted close to the hazard area and the enclosure can expose it directly to air. Pumped sampling is useful for remote points or ducts, but it adds tubing losses, pump delay and materials-compatibility requirements.
How should chlorine gas sensors be calibrated?
Use certified Cl2 calibration gas and a delivery system designed for reactive gas. Keep regulators, tubing and fittings compatible and minimize dead volume. Follow the finished detector procedure for flow rate, stabilization time and bump testing.
Final checks before design freeze
Validate the complete detector with the intended chlorine concentration, humidity, airflow, enclosure and sample path. The gas-delivery system is part of the measurement.
- Confirm the target is airborne Cl₂, not residual chlorine in water or ClO₂.
- Match measurement range and overload behavior to the credible release scenario.
- Review T90 and the full detector response through the final enclosure.
- Check NO₂, O₃, ClO₂ and other relevant cross-sensitivities.
- Keep condensation away from the sensor diffusion path.
- Validate chlorine-compatible tubing and fittings in pumped systems.
- Confirm the applicable industrial-safety and water-treatment requirements for the final instrument.
Need a chlorine gas sensor for an OEM project?
Send the target Cl₂ range, application, expected humidity, sampling method, response requirement and output interface. Manufacturers can also submit chlorine sensor models with an official product page and current datasheet.
Specifications and product availability can change. Confirm the latest manufacturer datasheet before engineering, compliance or purchasing decisions.