In drinking water treatment, swimming pool water quality management, bottled water production, cooling circulating water systems, and municipal water distribution networks, chlorine and related disinfection by-products have always been important indicators for water quality safety control. For general users, chlorine is often understood simply as a disinfectant. However, for system integrators, IoT solution providers, environmental engineering companies, and project contractors, chlorine management is not only about “adding” or “removing” chlorine. It is an engineering system involving dosing control, online monitoring, process linkage, data acquisition, alarm management, and long-term operation and maintenance.
Chlorine has strong oxidizing capability and can effectively inhibit bacteria, viruses, and some microorganisms in water. Therefore, it is widely used in drinking water disinfection and public swimming pool water treatment. However, when residual chlorine concentration is not properly controlled, or when it remains at a high level for a long period, it may cause pipeline corrosion, odor problems, increased disinfection by-products, process fluctuations, and user complaints. In engineering projects, if continuous online monitoring is absent and only manual sampling and laboratory testing are used, it is often difficult to promptly detect excessive dosing, residual chlorine decay, insufficient chlorine at the end of the pipe network, or equipment abnormalities.
Therefore, establishing a stable, integrable, and traceable online residual chlorine monitoring system is an important foundation for modern water treatment projects to achieve automated control and refined operation and maintenance.
The Role and Risk Boundary of Chlorine in Water Treatment Engineering
The core purpose of adding chlorine to water is to achieve disinfection control through oxidation. In drinking water treatment plants, secondary water supply systems, swimming pool circulation filtration systems, and industrial circulating water treatment, chlorine is usually used to control microbial growth and reduce biological contamination risks in water.
However, from the perspective of engineering control, higher chlorine concentration is not always better. If the residual chlorine concentration is too low, the disinfection effect may be insufficient. If the residual chlorine concentration is too high, it may intensify irritating odor, increase corrosion risks, raise the possibility of disinfection by-product formation, and affect the stable operation of subsequent process units.
Especially in drinking water projects, residual chlorine control usually needs to balance three objectives:
Finished water should have sufficient disinfection capability.
A reasonable level of residual chlorine should still remain at the end of the pipe network.
Water taste, corrosion, and by-product problems caused by excessive dosing should be avoided.
This means that what project sites require is not only a sensor, but also an online monitoring node that can work together with PLCs, data loggers, cloud platforms, or SCADA systems.
Common Chloride Risks and Their Impact on Engineering Projects
In practical projects, chlorine-related risks are mainly reflected in the following aspects:
1. Excessive or Insufficient Residual Chlorine in Drinking Water
If the residual chlorine concentration in drinking water systems is too low, disinfection may be insufficient. If it is too high, it may affect water taste and increase the risk of user complaints. For water plants, water distribution networks, and secondary water supply projects, residual chlorine monitoring points are usually arranged at the outlet, after chlorination, at key pipe network nodes, and at terminal water use points.
2. Water Quality Fluctuation in Swimming Pools
Residual chlorine in swimming pool systems changes rapidly and is significantly affected by the number of users, temperature, circulation filtration efficiency, replenishment water volume, and pH. Without real-time data, operators can only passively adjust the dosing amount, which can easily lead to excessive dosing or insufficient disinfection.
3. Imbalance Between Corrosion Control and Microbial Control in Cooling Circulating Water Systems
Oxidizing biocides are commonly used in cooling circulating water systems for microbial control. If residual chlorine is too low, algae and biofilm may grow. If residual chlorine is too high, it may aggravate corrosion of metal pipelines, heat exchangers, or sealing components. Therefore, online residual chlorine monitoring can help the system maintain a stable dosing range.
4. Lack of Feedback Data for Automation Control in Water Treatment Projects
In automatic dosing systems, if reliable residual chlorine feedback is unavailable, the system can only dose according to fixed time intervals or fixed flow rates, making it difficult to adapt to water quality fluctuations. By outputting RS485 Modbus signals through an online residual chlorine sensor, closed-loop data control can be achieved, improving system response capability.
Chlorine Removal and Control Methods
In engineering projects, chlorine control usually includes source dosing control, process monitoring, and terminal removal. Common removal methods include evaporation, filtration, and chemical neutralization.
Evaporation Method
Chlorine has a certain volatility and can naturally evaporate over time in an open environment. This method is suitable for small-scale or low-demand scenarios, but it has low efficiency in engineering projects and is not suitable for continuous treatment, large-flow water systems, or automated control projects.
Filtration Method
Reverse osmosis, activated carbon filtration, and other advanced treatment processes can reduce residual chlorine and some impurities in water. Among them, activated carbon is commonly used in drinking water advanced treatment and pretreatment systems, while reverse osmosis systems have stronger water purification capability. It should be noted that residual chlorine may affect some membrane materials, so configuring a residual chlorine monitoring point at the front end of membrane systems is of great importance.
Chemical Neutralization Method
Chemical neutralization usually removes residual chlorine quickly through the reaction between reducing agents and residual chlorine. It is suitable for some industrial water treatment, food and beverage, brewing, and process water applications. This method has a fast reaction speed, but the chemical dosing amount needs to be controlled to avoid secondary effects. Therefore, online residual chlorine monitoring can serve as an important feedback signal for neutralization control systems.
Why Engineering Projects Need Online Residual Chlorine Monitoring
Although traditional manual testing has a relatively low cost, it cannot meet the requirements of continuous monitoring, real-time alarm, remote management, and automatic control. In water plants, swimming pools, circulating water systems, and water distribution network projects, residual chlorine concentration may change rapidly over time due to temperature, pH, water flow velocity, organic load, and dosing amount.
The value of an online residual chlorine monitoring system is mainly reflected in the following aspects:
Real-time understanding of residual chlorine change trends.
Support for closed-loop control of automatic dosing systems.
Reduction of manual inspection frequency.
Easy access to PLCs, RTUs, data loggers, and cloud platforms.
Support for abnormal alarms and historical data traceability.
Improvement of project acceptance and operation management levels.
For system integrators, selecting a residual chlorine sensor with standard communication protocols, stable measurement performance, and clear installation conditions can reduce on-site commissioning costs and improve project delivery efficiency.
YexSensor YEX-S1-CL Residual Chlorine Sensor Engineering Application Solution
The YexSensor YEX-S1-CL residual chlorine sensor is suitable for continuous online monitoring of residual chlorine content in aqueous solutions. It can be applied in drinking water treatment plants, bottled water production lines, drinking water distribution networks, swimming pools, cooling circulating water, water quality treatment projects, and other scenarios.
The sensor adopts the constant voltage measurement principle and supports RS485 bus and Modbus RTU protocol, making it easy to connect to PLCs, data loggers, IoT gateways, SCADA systems, and cloud platforms. For projects that require remote monitoring, automatic dosing, and data visualization platforms, this interface format provides good engineering compatibility.
YEX-S1-CL Technical Specifications
| Parameter Item | Technical Specification |
|---|---|
| Model | YEX-S1-CL |
| Measuring Principle | Constant voltage method |
| Range Ability | 0～2.000 mg/L HClO |
| Resolution | 0.001 mg/L |
| Precision | ±5% or ±0.05 mg/L, ±0.5 ℃ |
| Calibration Function | Two-point calibration, zero and slope |
| Working Pressure | ＜0.1 MPa |
| pH Range of the Medium | 4～9 pH |
| Temperature Compensation | Automatic temperature compensation, Pt1000 |
| Signal Output | RS485 bus, Modbus RTU protocol |
| Material | POM polyoxymethylene, Polytef |
| Working Temperature | 5～50 ℃ |
| Installation Mode | Circulation pool installation |
| Dimension | 30 × 233 mm |
| Flow Speed | 30～60 L/h |
| Response Time | ＜30 s |
| Power Supply | 12～24 VDC ±10% |
| Power | 0.2 W @ 12 V |
| Protection Grade | IP68 |
Typical System Integration Architecture
In water treatment projects, YEX-S1-CL can be used as a sensing-layer device connected to the overall automation system. The typical architecture is as follows:
The on-site water sample enters the sensor measurement unit through the flow cell. The sensor outputs residual chlorine data in real time and transmits it to the PLC, RTU, or data logger through RS485 Modbus RTU. The system can further upload data to local SCADA, HMI touch screens, or cloud platforms to realize trend analysis, alarm records, remote viewing, and dosing control.
In automatic dosing projects, the PLC can control metering pumps, dosing valves, or variable-frequency dosing systems according to the deviation between the residual chlorine set value and the real-time measured value, achieving more stable residual chlorine control.
Typical Application Scenarios
Drinking Water Treatment Plants
In drinking water treatment plants, residual chlorine sensors can be installed at finished water outlets, clear water tank outlets, downstream of chlorination points, and key process nodes to evaluate disinfection performance and dosing stability. Through continuous monitoring, manual sampling frequency can be reduced, and finished water quality management capability can be improved.
Drinking Water Distribution Networks
Insufficient residual chlorine at the end of the pipe network is a common problem in water supply systems. By arranging online residual chlorine monitoring equipment at key pipe network nodes, operators can understand residual chlorine decay and support optimization of chlorination strategies and network scheduling.
Swimming Pool Water Quality Monitoring
Swimming pool water quality is greatly affected by the number of users, circulation flow, and temperature. YEX-S1-CL can be used for online monitoring of residual chlorine in swimming pool circulating water and can work with dosing equipment to improve water quality management efficiency.
Cooling Circulating Water Systems
In cooling circulating water projects, residual chlorine monitoring helps control the dosing level of biocides, avoiding insufficient dosing or equipment corrosion caused by excessive dosing, and providing stable operating data for industrial circulating water systems.
Water Quality Treatment Engineering and System Integration Projects
For engineering companies and system integrators, YEX-S1-CL can be integrated as a standardized water quality monitoring module into water treatment equipment, skid-mounted systems, online monitoring stations, or IoT monitoring platforms.
Selection Guide: How to Determine Whether YEX-S1-CL Is Suitable for a Project
When selecting a residual chlorine sensor, the following engineering conditions are recommended for confirmation:
1. Whether the Measurement Target Is Residual Chlorine
YEX-S1-CL is suitable for continuous monitoring of residual chlorine content in aqueous solutions, especially for HClO detection requirements in drinking water, swimming pools, circulating water, and water treatment engineering.
2. Whether the Concentration Range Matches the Project
The measurement range of this model is 0～2.000 mg/L. If the residual chlorine concentration in the project remains higher than this range for a long time, it should be confirmed in advance whether a higher-range model or a sampling dilution solution is required.
3. Whether the On-Site pH Is Within the Range of 4～9
Residual chlorine measurement is significantly affected by pH. The applicable medium pH range of this sensor is 4～9, so the on-site water quality conditions should be confirmed during project design.
4. Whether a Flow Cell Can Be Configured
YEX-S1-CL adopts flow cell installation and is recommended to maintain a stable flow rate of 30～60 L/h. For engineering projects, the flow cell helps improve measurement stability and reduce the influence of water flow fluctuation on data.
5. Whether the Control System Supports RS485 Modbus RTU
The sensor supports RS485 Modbus RTU protocol and is suitable for connection to PLCs, data loggers, RTUs, IoT gateways, and SCADA systems. Before project integration, register addresses, communication parameters, power supply mode, and wiring distance should be confirmed.
Integration Considerations
Maintain Stable Flow Rate
Residual chlorine measurement has flow rate requirements. It is recommended to maintain a flow rate of 30～60 L/h through a flow cell, flow stabilization device, or sampling bypass to avoid response delay caused by low flow rate or measurement instability caused by excessive flow rate.
Pay Attention to pH and Temperature Effects
Although the sensor is equipped with Pt1000 automatic temperature compensation, pH still affects the existing form of residual chlorine. It is recommended to monitor pH simultaneously during system design, especially in automatic dosing or drinking water treatment projects.
Arrange Sampling Points Reasonably
Sampling points should avoid bubbles, sediments, strong disturbance, and dead water zones. For chlorination systems, monitoring points should be arranged downstream after sufficient mixing to avoid excessive data fluctuation.
Perform Regular Calibration and Maintenance
Online sensors need maintenance plans according to on-site water quality conditions. It is recommended to regularly check the flow cell, clean the electrode surface, and conduct zero and slope calibration according to project requirements.
Use Together with Control Logic
In automatic dosing systems, it is not recommended to control dosing equipment directly based only on instantaneous values. Average values, delay judgment, upper and lower limit alarms, and PID control logic can be combined to improve system stability.
FAQ
Q1: Is YEX-S1-CL suitable for drinking water projects?
Yes. YEX-S1-CL can be used for continuous residual chlorine monitoring in drinking water treatment plants, drinking water distribution networks, and related water quality treatment projects. It supports RS485 Modbus RTU output, making it convenient to connect to automation systems.
Q2: Can this sensor be directly connected to a PLC?
Yes. YEX-S1-CL supports RS485 bus and Modbus RTU protocol. It can usually be connected to PLCs, RTUs, data loggers, or IoT gateways that support Modbus communication.
Q3: Does YEX-S1-CL require a flow cell?
Yes. This model adopts flow cell installation, and the recommended flow rate is 30～60 L/h. The flow cell can improve measurement stability and facilitate engineering site maintenance.
Q4: Is this sensor suitable for swimming pool water quality monitoring?
Yes. Residual chlorine in swimming pool water changes frequently. YEX-S1-CL can be used for online monitoring of residual chlorine in circulating pool water and can work with dosing systems for automatic control.
Q5: Can the residual chlorine sensor be used in cooling circulating water?
Yes. Cooling circulating water systems often need to control the dosing of oxidizing biocides. Online residual chlorine monitoring can help avoid insufficient dosing or excessive dosing.
Q6: What is the measurement range of this sensor?
The measurement range of YEX-S1-CL is 0～2.000 mg/L HClO, which is suitable for low-range residual chlorine monitoring scenarios. If the on-site concentration is relatively high, the project range requirements should be confirmed in advance.
Q7: Is residual chlorine measurement affected by pH?
Yes. The existing form of residual chlorine in water is related to pH. The applicable medium pH range of YEX-S1-CL is 4～9, so pH conditions should be considered in engineering projects.
Q8: Is YEX-S1-CL suitable for batch projects by system integrators?
Yes. The sensor provides standard RS485 Modbus RTU output, low power consumption, IP68 protection grade, and clear flow cell installation conditions. It is suitable for water treatment equipment integration, monitoring stations, cloud platform access, and automatic dosing control projects.
Conclusion
Chlorine plays an important disinfection role in drinking water, swimming pools, cooling circulating water, and water treatment engineering, but its concentration must be controlled within a reasonable range. For engineering projects, residual chlorine management should not remain at the level of manual testing. Instead, continuous, digital, and traceable management should be achieved through online residual chlorine sensors, standard communication protocols, automation control systems, and remote platforms.
The YexSensor YEX-S1-CL residual chlorine sensor is designed for engineering applications and supports RS485 Modbus RTU protocol. It is suitable for drinking water treatment plants, bottled water production, water distribution networks, swimming pools, cooling circulating water, and water quality treatment projects. For system integrators, IoT solution providers, and project contractors, this product can serve as a key sensing node in online residual chlorine monitoring and automatic dosing control systems, helping projects achieve stable operation, data closed loop, and long-term operation and maintenance optimization.
