Walchem Amperometric Disinfection Sensors (Chlorine Dioxide, Peracetic Acid, Hydrogen Peroxide, Ozone, Chlorite)

Walchem amperometric disinfection sensors measure the concentration of an oxidizing disinfectant directly and continuously, without reagents and without discarding the sample. The sensor family covers chlorine dioxide, peracetic acid (PAA), hydrogen peroxide, ozone and chlorite, and Walchem also supplies chlorine, bromine and stabilized bromine sensors. Each sensor connects to a Walchem controller and sits in a flow cell. As the Walchem distributor in Turkey, Mikron Proses (Üsküdar, Istanbul) supplies the sensors, flow cells, membrane caps and electrolyte, and provides application consulting for sensor and controller selection, commissioning and calibration support.

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Selection table by parameter

Parameter	Ranges (ppm)	Sample pH	Response / conditioning	Pressure	Main interferences
Chlorine dioxide (ClO₂)	0-2, 0-20	1-12	1.5 min / 60 min	1 bar	Ozone (2500%)
Peracetic acid (PAA)	0-200, 0-2000, 0-20000	1-6	3 min / 3 hours	1 bar	Ozone (2500%), ClO₂ (100%), H₂O₂
Hydrogen peroxide (H₂O₂)	0-200, 0-2000, 0-20000	2-11	8 min / 5 hours	1 bar	Not affected by chlorine, PAA and ozone
Ozone (O₃)	0-2, 0-20	4-9	8 min / 60 min	1 bar	Chlorine (1.5%), ClO₂
Chlorite	0-2	6-9	1 min / 24 hours	5 bar	Mn²⁺, Fe²⁺, nitrate

Each parameter is offered in more than one range with separate part numbers, so the range can be matched to the expected concentration. A range that is wider than needed gives a coarser resolution at low concentrations. The sensors differ in their interference profiles: for example the hydrogen peroxide sensor is not affected by chlorine, PAA or ozone, while the ozone sensor responds slightly to chlorine (1.5%) and to chlorine dioxide.

Sample conditions and maintenance

All sensors need a steady sample flow of 30-100 L/h and a conductivity of at least 10 µS/cm. The permitted sample pH differs by sensor, from the wide range of the chlorine dioxide sensor (pH 1-12) to the narrow range of the PAA sensor (pH 1-6). Calibration is weekly for every sensor; PAA is calibrated by thiosulfate titration and ozone by the DPD-4 method. Conditioning time after installing a new sensor ranges from 60 minutes for chlorine dioxide and ozone to 24 hours for chlorite. Electrolyte stored in its original bottle at 5-35 °C, protected from sunlight, lasts one year or until its expiry date, and a sensor stored dry without electrolyte has an unlimited shelf life.

Controller connection

The sensors are powered with ±5 VDC (10 mA maximum) and give a signal from 0 to -2000 mV DC, which can be extended up to 30 m with a shielded 22 AWG cable (Walchem 100084). The brochure lists the W100, W600 and W900 series controllers, and the Intuition-6 and Intuition-9 brochures include disinfection sensor options as well; see the Intuition-6 series, the Intuition-9 series and the W100P panel-mount controller. Choose one sensor and one flow cell (panel flow switch manifold or flow cell). For related background see the hydrogen peroxide measurement guide, the pool chlorine measurement guide and the Walchem brand page.