For online monitoring of residual chlorine in swimming pools, why is a membrane-covered residual chlorine sensor preferred?

Accurate measurement of residual chlorine levels in swimming pools is crucial to protecting swimmers’ health. YuanGan Technology has launched two types of residual chlorine sensors, DP and DPM. DP is a film-less (bare electrode) residual chlorine sensor, and DPM is a membrane-covered residual chlorine sensor. For most swimming pool residual chlorine online monitoring application scenarios, it is first recommended to use DPM coated residual chlorine sensors.

The reasons for recommendation are as follows:

1 Cyanuric acid has little impact (the most important)

Most (more than 80%) public swimming pools use trichloroisocyanuric acid (TCCA) as a disinfectant. After trichloroisocyanuric acid disinfection, a large amount of cyanuric acid will remain in the water. Chlorine lock-in occurs when there are high levels of cyanuric acid in a swimming pool. At this time, the measured value of the membraneless (bare electrode) residual chlorine sensor is significantly lower than the measured value of the DPD or OTO reagent method.

DPM isolates the working electrode from the external water sample through a permeable membrane. Compared with the membrane-less (bare electrode) residual chlorine sensor, cyanuric acid has a much smaller impact on the DPM-coated residual chlorine sensor. Therefore, the measured value of the DPM-coated residual chlorine sensor in a public swimming pool disinfected by trichloroisocyanuric acid (TCCA) is more stable.

2. Strong anti-pollution ability

The working electrode of the DP filmless (bare electrode) residual chlorine sensor is exposed, and its working electrode is in direct contact with the water sample.

The DPM-coated residual chlorine sensor isolates the working electrode from external water samples through a permeable membrane. The working electrode is not easily contaminated and the measurement is more stable.

3. Little impact on flow rate

The residual chlorine sensor adopts the ampere current method measurement principle, and its sensor current intensity is easily affected by the flow rate of the water sample.

Due to the existence of the permeable membrane of the DPM-coated residual chlorine sensor, the water flow will not directly act on the surface of the working electrode. Therefore, compared with the membrane-less (bare electrode) residual chlorine sensor, the water sample flow rate has a much smaller impact on the DPM-coated residual chlorine sensor.

4 pH changes have little impact

Residual chlorine (abbreviation for free residual chlorine) is composed of two components: hypochlorous acid and hypochlorite.

Hypochlorous acid and hypochlorite have different proportions when the water sample has different pH, and the redox potential of the two is very different. Therefore, the current intensity of the sensor's response to the two is very different.

The electrolyte in the membrane head of the DPM-coated residual chlorine sensor can buffer changes in the pH of the water sample to a certain extent. Therefore, compared with the membrane-less (bare electrode) residual chlorine sensor, the DPM-coated residual chlorine sensor has a more stable measurement when the pH of the water sample fluctuates.

Precautions for coated residual chlorine sensor

When using a coated residual chlorine sensor, you need to pay attention to maintaining the continuity of residual chlorine in the swimming pool. Otherwise, long-term lack of chlorine will easily breed bacteria, causing the membrane head of the coated residual chlorine sensor to become clogged, resulting in abnormal measurement.

In summary, the DPM-coated residual chlorine sensor shows significant advantages in terms of the influence of cyanuric acid, anti-pollution ability, flow rate influence, and pH change. Compared with membrane-less (bare electrode) residual chlorine sensors, it can provide more stable and accurate measurement results for online monitoring of residual chlorine in swimming pools. As long as the residual chlorine in the swimming pool is (and should be) maintained, its advantages can be fully utilized.