Do You Know the Hazards Associated with Residual Chlorine Analyzers?

A residual chlorine analyzer is a highly intelligent online continuous monitoring instrument composed of a sensor and a secondary meter. It can simultaneously measure residual chlorine, pH value, and temperature. It is widely used for continuous monitoring of residual chlorine and pH values in various water qualities across industries such as electric power, water plants, and hospitals.

1. Tap water mostly uses chlorine for disinfection. When chlorine dissolves in water, it turns into hypochlorous acid (HClO) or hypochlorite ions (ClO-), commonly known as effective residual chlorine. Because hypochlorous acid has a very high oxidative capacity, its presence in tap water prevents bacterial growth (pathogens) from remaining in the distribution pipes. Therefore, effective residual chlorine plays a vital role in the safety and hygiene of tap water.

2. Using chlorine-based disinfectants for tap water disinfection and sterilization is popular because it is inexpensive, effective, easy to operate, and safe to use. However, while chlorine has a strong killing effect on bacterial cells, it also has a serious impact on other biological cells and human cells.

3. In 1974, Rook from the Netherlands and Belier from the United States discovered that pre-chlorinated and chlorinated water contains disinfection by-products (DBPs) such as trihalomethanes (THMs) and chloroform, which have carcinogenic and mutagenic effects. In the mid-1980s, it was discovered that another group, haloacetic acids (HAAs), pose an even greater carcinogenic risk. For example, chloroform, dichloroacetic acid (DCA), and trichloroacetic acid (TCA) are 50 and 100 times more carcinogenic than chloroform, respectively. To date, with the advancement of science and technology, 2,221 types of organic pollutants have been detected in water sources, and 65 types have been found in tap water, including 20 carcinogens and 56 mutagens.

4. To ensure tap water meets safety and hygiene requirements and to avoid the occurrence of waterborne infectious diseases, disinfectants should be added during the water purification process to inactivate pathogenic microorganisms in the water. Due to its high cost-effectiveness, chlorine is widely used in the domestic water treatment industry.

5. Residual chlorine refers to the amount of chlorine remaining in the water after it has been added, following the consumption of a portion of the chlorine through interaction with bacteria, microorganisms, organic matter, and inorganic matter in the water. This remaining amount is called residual chlorine. Residual chlorine can be divided into combined residual chlorine and free residual chlorine. Total residual chlorine is the sum of combined and free residual chlorine.

6. If there is no chlorine or insufficient chlorination in the factory water, microorganisms such as bacteria and E. coli may proliferate in the pipe network, affecting water quality. Therefore, the water supply network must guarantee a certain amount of residual chlorine.

7. China's "Standards for Drinking Water Quality" stipulate that after 30 minutes of contact with water, the chlorine content must not be lower than 0.3 mg/L. In addition to factory water, centralized water supply should meet the above requirements, and the water at the end of the pipe network must not be lower than 0.05 mg/L.

I. Application Environment Description

Used in drinking water treatment plants, bottling plants, drinking water distribution networks, swimming pools, cooling circulation water, water quality treatment engineering, and other occasions requiring continuous monitoring of residual chlorine content in aqueous solutions.

II. Technical Performance and Specifications

1. Technical Parameters

Note: The sensor connector is an M16-5 pin waterproof male plug.

III. Electrical Connection

1. Installation
Use the matching flow cell for installation. Ensure the sensor and flow cell are tightly installed. The measurement part of the sensor should be placed near the inlet area of the flow cell and should not directly face the outlet to ensure stable flow. It is recommended to control the flow rate at 30-60 L/h to ensure measurement accuracy.

2. Electrical Connection
The cable is a 4-core twisted pair shielded wire. Line sequence definition:

• Red wire—Power positive (12～24VDC)

• Black wire—Power negative (GND)

• Blue wire—485A

• White wire—485B

• Yellow wire—Current output (Optional 5-core shielded wire)

Check the wiring sequence carefully before powering on to avoid unnecessary losses. All wiring points must be waterproofed, and user cables should have certain anti-corrosion capabilities.

IV. Maintenance and Care

1. Detection and Maintenance
New or long-stored electrodes need activation before use; place the sensor in tap water for 24 hours. If readings are inaccurate, calibrate the zero point and slope or return to the factory for inspection.

2. Calibration
a) Zero Point Calibration: Place the sensor in chlorine-free water and calibrate after the value stabilizes.
b) Slope Calibration: Place the sensor in a flow cell with circulating residual chlorine standard solution (recommended 1-2mg/L HClO) and calibrate after stability.

FAQ Section

Q1: Why is real-time monitoring of residual chlorine critical for system integrators?
Beyond ensuring sterilization, real-time monitoring is essential to control the formation of carcinogenic disinfection by-products (DBPs) like THMs. Accurate dosing feedback via YEX-S1-CL allows for a closed-loop system that balances public safety with toxicological risk mitigation.

Q2: What is the advantage of the Constant Voltage Method over traditional DPD methods?
The YEX-S1-CL uses a non-membrane constant voltage principle, which requires no reagents and has a much lower maintenance frequency compared to DPD-based online analyzers, making it ideal for unmanned IoT monitoring stations.

Q3: How do I ensure the best accuracy during installation?
Flow stability is paramount. Always use the recommended flow cell and maintain a flow rate between 30-60 L/h. Avoid placing the sensor probe directly in the path of the outlet to prevent turbulence-induced noise in the RS-485 data signal.

Q4: Is the YEX-S1-CL compatible with standard industrial PLCs?
Yes. It supports the standard RS-485 Modbus RTU protocol, allowing seamless integration with PLCs, RTUs, and industrial IoT gateways for remote data acquisition and control.

Q5: What are the consequences of insufficient residual chlorine in a distribution network?
Insufficient levels lead to microbial regrowth, including E. coli and other pathogens, within the pipe network. This compromises the safety of the entire supply chain and violates national health standards.

Q6: Does the sensor require frequent cleaning?
The constant voltage design is relatively resistant to fouling. However, for applications with high organic loads, periodic inspection of the electrode surface is recommended. Regular activation in tap water helps maintain the electrode's sensitivity.

Q7: How does pH affect the measurement of residual chlorine?
Residual chlorine chemistry is highly pH-dependent (HClO vs ClO-). The YEX-S1-CL functions optimally between pH 4-9 and includes automatic temperature compensation to ensure data integrity across varying environmental conditions.

Q8: What is the significance of the IP68 rating for this analyzer?
The IP68 rating ensures that the sensor is completely dust-tight and can withstand long-term immersion under pressure. This makes it suitable for harsh industrial environments, including outdoor water distribution cabinets and hospital wastewater facilities.

Summary

Effective water disinfection requires more than just adding chlorine; it requires precision monitoring to avoid the production of harmful carcinogens. For system integrators and project contractors, the YexSensor YEX-S1-CL provides a robust, digital, and low-maintenance solution for ensuring regulatory compliance and public health safety. By integrating advanced constant voltage sensing with industrial-grade RS-485 communication, we provide the core data layer needed for modern, safe, and efficient water treatment infrastructure.