In July 2025, a special 'endurance race' was taking place in a constant temperature chamber of a laboratory under the National Urban Water Supply Quality Monitoring Network. Four residual chlorine online analyzers from different brands were placed in the same simulated pipeline water environment and operated continuously for 30 days without interruption. When the experimenters released the data on the 31st day, the results shocked the representatives of the 12 water supply companies present: CLG-2060, which used DPD colorimetric method, lagged far behind the three competitors using electrochemical method with a comprehensive error of ± 3.2% and a drift rate of 0.8%, among which the error value of a certain imported brand was as high as ± 17.5%. This rigorous horizontal evaluation so far has revealed the 'parameter fog' of the residual chlorine monitoring equipment market using laboratory data.

Explanation of Test Samples and Evaluation Dimensions

The top four residual chlorine online analyzers selected for this horizontal evaluation are:

• CLG-2060 (A brand): DPD colorimetric method, with a range of 0.00-10.00mg/L

• EC-3000 (B brand): Electrochemical method, with a range of 0.01-5.00mg/L

• ColorGuard Pro (C brand): DPD colorimetric method, with a range of 0.05-2.00mg/L

• SmartChlor M5 (D brand): Electrochemical method, with a range of 0.00-2.00mg/L

The test was conducted in a nationally recognized CNAS laboratory, simulating typical operating conditions of a drinking water pipeline network (water temperature 15-25 ℃, pH 6.5-8.5, turbidity<10 NTU), using the HJ 586-2010 national standard method as a reference. The test was conducted from four core dimensions: measurement accuracy, range coverage, stability performance, and anti-interference ability. Each test was repeated three times and the average value was taken.

Precision showdown: DPD colorimetric method shows overwhelming advantage

In the commonly used range of 0.05-4.00mg/L for municipal water supply, the performance of the four devices showed significant differentiation. The measurement error of CLG-2060 at a low concentration point of 0.05mg/L is only+3.2%, while the errors of both electrochemical devices exceed+15%, with the B brand EC-3000 even showing a negative deviation of -22%. More noteworthy is the concentration mutation test: when the residual chlorine value of the water sample was suddenly increased from 0.5mg/L to 3.5mg/L, the response time of CLG-2060 was 45 seconds, reaching 90% of the final value, while the D brand equipment took up to 3 minutes and 20 seconds and showed obvious overshoot.

The electrode of electrochemical method is easily affected by dissolved oxygen and temperature in water, "explained Wang Gong, a water quality analyst who participated in the test." In the micro detection scenario of residual chlorine in pipeline water, the specific color reaction advantage of DPD colorimetric method is obvious. The data shows that in the range of 0-5mg/L, the average error of CLG-2060 remains stable at ± 3.8%, which is in line with its claimed ± 5% accuracy index. However, the errors of the two electrochemical devices show an upward trend over time and have exceeded ± 10% by the 15th day.

Range coverage and scene adaptability testing

Although the C brand ColorGuard Pro also uses the DPD colorimetric method, it is limited by a narrow range of 0.05-2.00mg/L. On the 8th day of testing, it triggered an over limit alarm due to a short-term increase in simulated residual chlorine in the pipeline network to 2.8mg/L. This situation is not uncommon in practical applications - records from a water supply company in a coastal city show that the residual chlorine value often fluctuates between 3-4mg/L when adjusting the chlorine dosage during the rainy season.

The wide range design of CLG-2060 from 0.00-10.00mg/L demonstrates significant advantages, with no over range incidents occurring throughout the entire testing process. More importantly, its range linearity: the linear correlation coefficient R ² is 0.998 in the low concentration range of 0.00-1.00mg/L, and remains at 0.996 in the high concentration range of 1.00-10.00mg/L. However, the linearity of B brand has decreased to 0.972 at concentrations above 2.00mg/L, showing significant nonlinear deviation.

30 day stability test exposes the true quality of the product

Stability testing can be regarded as the 'marathon test' of equipment. Experimental data shows that there is a significant difference in drift rate among the four devices starting from the 10th day: the zero drift of CLG-2060 is always controlled within ± 0.01mg/L, while the zero drift of B brand EC-3000 has reached -0.08mg/L by the 30th day, which is equivalent to 160% of the national standard limit.

The effectiveness of the automatic calibration function has become a watershed in stability. The automatic calibration cycle of CLG-2060 every 7 days keeps the equipment stable for a long time, while the C brand that requires manual calibration did not calibrate in time on the 21st day, and the deviation between the measured value and the standard value increased to+9.7%. This explains why many water plants report that the equipment becomes more and more inaccurate as it is used, "Wang pointed out." The passivation effect of electrochemical electrodes and the stability of DPD reagents determine that there is a fundamental difference in maintenance requirements between the two types of equipment. '

Anti interference capability: a 'magic mirror' for complex water quality in pipeline networks

In the interference water sample test with intentionally added iron ions (0.3mg/L) and organic matter (UV254=0.1cm ⁻¹), the error of CLG-2060 only increased by 1.2 percentage points, while the errors of the two electrochemical devices soared to+27.3% and -31.5%, respectively. D brand equipment even experienced data lock due to electrode poisoning and needs to be sent back to the factory for activation treatment.

This test replicates the water quality incident of a provincial capital city's pipeline network in 2024- at that time, due to pipeline corrosion, iron ions exceeded the standard, and the monitoring system using electrochemical methods falsely reported zero residual chlorine, causing a large-scale water outage panic. Post investigation shows that this false alarm can be avoided if DPD colorimetric equipment is used.

Evaluation Conclusion and Selection Suggestions

The laboratory data clearly shows that in the monitoring scenario of residual chlorine in drinking water pipe networks, CLG-2060 demonstrates comprehensive advantages with DPD colorimetric method, wide range design, and stable automatic calibration system. Its range coverage of 0.00-10.00mg/L meets the full scenario monitoring requirements from water source to the end of the pipeline network. The accuracy index of ± 5% is even better than the nominal value in actual testing, and the drift rate of 0.8% in 30 days has set a new industry standard.

For the selection of water supply enterprises, this evaluation provides three suggestions:

1. Prioritize DPD colorimetric method: Under residual chlorine concentration in municipal water supply (0.05-4mg/L), the accuracy and anti-interference performance are significantly better than electrochemical method

2. Pay attention to the actual range rather than the nominal value: It is recommended to choose a range of 0.00-5.00mg/L or above to cope with water quality fluctuations

3. Automatic calibration is essential: at least one automatic calibration per month can significantly reduce maintenance costs and human errors

After reviewing the evaluation report, the technical director of a water management group in a first tier city decided on the spot to replace all 50 monitoring devices purchased in the next batch with CLG-2060. We have calculated that although the cost of a single device is 15% higher, the maintenance and calibration costs saved over three years can cover the price difference. More importantly, the security value brought by data reliability is incalculable

This 30 day extreme test not only provides a scientific selection basis for water supply enterprises, but also reveals an industry truth: in today's increasingly severe drinking water safety, the performance differences of residual chlorine monitoring equipment are no longer simply parameter comparisons, but a major livelihood issue related to the water safety of thousands of households. As more and more water supply companies begin to speak with data, the 'pseudo precision' equipment packaged by marketing rhetoric will eventually be eliminated by the market. The technology powerhouse represented by CLG-2060 is driving the industry from 'qualified is standard' to a higher standard of 'precision is safety'.