Overview
This article explains why pH is a key variable in free chlorine measurement and how Kuntze systems with chlorine and pH measurement can compensate pH influence to improve measurement stability.
Key takeaways:
- Free chlorine in water is present as HOCl and OCl-
- Amperometric free chlorine measurement responds primarily to HOCl
- The HOCl/OCl- ratio shifts with pH and changes the measured signal
- Kuntze systems that include pH measurement can apply compensation for more reliable operation
Why pH Matters
In chlorinated water, free chlorine is distributed between hypochlorous acid (HOCl) and hypochlorite (OCl-). Since the free chlorine sensor signal is tied mainly to HOCl, a pH shift changes the apparent measurement even if total free chlorine in water is unchanged.
At lower pH, the HOCl fraction is higher and measurement conditions are generally more favorable. As pH increases, HOCl decreases and measurement sensitivity becomes more challenging. For this reason, stable pH conditions are essential for accurate control.
How Kuntze Systems Compensate
Kuntze analyzers that measure both pH and free chlorine can apply compensation logic in the analyzer. This helps reduce pH-related deviations and supports durable, reproducible chlorine readings for dosing and process control.
Note: Compensation availability depends on system configuration and selected measurement parameter.
Video Tutorial
The video explains the pH influence on free chlorine measurement using Krypton® Multi as an example.
Direct link: https://play.vidyard.com/daBRyUQMinFnofGpfVNHts
Practical Notes
- Keep pH stable during commissioning and calibration
- Avoid large pH swings when evaluating chlorine drift
- Always compare online values against a clean and valid reference method
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