Free Chlorine Measurement Instrumentation

How is free chlorine measured?

There are two basic methods for Free Chlorine Measurement in water; Colorimetric analysis and Amperometric analysis.

Colorimetric measurement can be further divided between a simple test strip method and a more accurate Photometer/Colorimeter measurement using free chlorine instrumentation. A Photometer/Colorimeter measurement is achieved with the addition of a DPD reagent in a given sample size, and using an optical instrument to read the results. A deeper colour indicates the presence of more Chlorine and the chlorine instrument can determine the relationship between the colour intensity and corresponding chlorine concentration.

Amperometric analysis consists of a sensor which returns a voltage value, interpreted as concentration. The most accurate free chlorine instrumentation includes both temperature and pH measurement.

For online continuous measurement, the  ‘Trides’ Amperometric free chlorine analyzer provides Chlorine measurement in a compact, reliable and extremely accurate instrument. Consisting of two platinum electrodes and a reference electrode with a liquid junction for accurate measurement. The electrode has an extremely long service life. The design is innovative with a built in flow detector and continuous sensor cleaning. Integrated pH measurement for the automatic calculation of Free Chlorine at changing pH levels. The pH sensor is also located in a flow chamber where at no flow conditions it remains wet.

Which is the correct method for online, continuous measurement?

The answer lies in an analysis of the quality and potential contaminants within the sample.

Amperometric is a desired option due to substantial cost saving, low maintenance, no DPD required and no chemicals to dispose of. However high levels of certain “interference” minerals can cause the sensor to output incorrect results.

Colorimetric measurement is used in situations where the sample water is less than ideal Due to the nature of the measurement, optics are used to read colour intensity. There is no sensor in contact with the water so it cannot be affected by contaminants.

Which is the best hand held instrument?

For most applications a  Colorimetric hand-held chlorine meter is sufficient. Beyond this initial requirement, consider convenience as a large factor. Multi parameter meters area great option if multiple measurements are being performed. One example of a popular, and field proven meter is the Turbidity/Free Chlorine/Total Chlorine Meter Which can easily switch between three key measurement parameters.