Tech Insights

Detailed explanation of the "film coating method" of residual chlorine sensors

Nov 17, 2025·Official source

Puzzle-solving class: Clear up the fog - Detailed explanation of the essential consistency between the "coating method" and the "exposure type" of the residual chlorine sensor

In the field of online residual chlorine monitoring, we often hear the terms "membrane-covered sensor" and "exposed sensor". Some people even call the membrane-covered sensor "coating method" and discuss it in parallel with the "ampere current method". This has caused confusion in technical concepts to a certain extent. Chongqing YuanGan Technology will clarify it for you through this article: These two sensors are completely identical in core principles, and the only difference lies in the physical structure and applicable scenarios.

1. Consistency of core principles: both are ampere current method

1. Same electrochemical basis

Whether it is a film-covered or exposed double platinum ring sensor, its core measurement principle is the ampere current method. Core features of this approach include:

Constant working potential: the working electrode maintains a constant potential relative to the reference electrode
Current detection: Measure the current signal generated by the reaction of electroactive substances on the electrode surface
Concentration proportional: The current size is proportional to the concentration of the target substance

2. Same electrode reaction

Both sensors are based on the same electrochemical reaction:

HClO + H⁺ + 2e⁻ → Cl⁻ + H₂O

Hypochlorous acid obtains electrons on the surface of the working electrode and is reduced, and the reduction current generated is proportional to the concentration of residual chlorine.

2. Differences in technical implementation: differences in physical structure

1. Structural features of membrane-covered sensors

The film-covered sensor adopts the design of "three electrodes + selective breathable membrane":

Membrane protection system: The electrode system is isolated from the water sample through a special selective breathable membrane
Stable internal environment: the electrode works in a stable electrolyte environment
Strong anti-interference: the membrane effectively blocks most impurities and interference substances

2. Structural characteristics of exposed sensors

Exposed sensors also use a three-electrode system:

Direct contact: the working electrode and counter electrode are directly exposed to the water sample
Built-in reference electrode: The reference electrode is protected through special design
Fast response: no membrane barrier, faster response

3. Correctly understand the term “coating method”

1. The "coating method" is a morphological description, not a principle distinction.

It is inaccurate to refer to membrane-covered sensors as "membrane-covered sensors" in the industry because:

"Coating" describes the physical structural characteristics
"Amperometric method" describes the principle of electrochemistry
The two are concepts at different levels and should not be compared side by side.

2. Vivid metaphor understanding

We can use a vivid metaphor to understand the relationship between the two:

Covered and exposed sensors are like shielded and open balances - they all measure weight based on the same lever principle (amperometric method) and only differ in the form of protection.

4. Comparative analysis of the two structures

5. Selection suggestions: based on application scenarios rather than principles

1. Scenarios for selecting membrane-type sensors

Medical wastewater treatment plant effluent monitoring
Automatic swimming pool water quality control
Situations with complex water quality and many interferences

2. Select the scenario for exposed sensors

Drinking water treatment process monitoring
Industrial circulating cooling water system
Monitoring points with relatively clean water quality

6. Technical perspectives of Chongqing YuanGan Technology

Based on our profound technical accumulation, we put forward the following views:

1. Terminology standardization suggestions

Accurate description: Amperometric sensor (membrane-covered)
Exact description: Amperometric sensor (exposed)
Avoid using the confusing term "laminated method"

2. Technology development prospects

The two technical routes will coexist for a long time, each serving suitable application scenarios.
Technological innovation should focus on improving measurement accuracy and stability rather than creating new concepts
Promote the industry to establish a unified and standardized technical terminology system

Conclusion

Covered and exposed residual chlorine sensors are "twin brothers". They are connected by blood (the same amperometric principle), but they are dressed differently (different physical structures). Understanding this essence will help us make more scientific choices in practical applications and promote the healthy development of industry technology.

Chongqing YuanGan Technology Co., Ltd., as a professional water quality monitoring solution provider, also provides film-covered and exposed residual chlorine sensors based on the same principle. We will continue to uphold a scientific and rigorous attitude to provide customers with the most appropriate technical solutions and accurate product information.

—— Chongqing YuanGan Technology Co., Ltd. uses professionalism to protect water quality safety