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An often overlooked part of a chlorine analyzer system is a chart recorder.

Choosing a Chlorine Analyzer

by RWI

     How do you pick a chlorine analyzer to fit your needs?  There are a lot of things to consider before deciding on an analyzer including economics, technical issues, control, dependability and ease of use.

 

There are a lot of things to consider before deciding on a chlorine analyzer.

Economics

     More so today than ever, economics play a major role in determining what equipment to purchase.  Choosing a chlorine analyzer need not be expensive as there are many good and inexpensive analyzers available.  Yet selecting an analyzer solely on whether it is affordable may be dangerous because it may not do what it is supposed to do.  Operating and repair costs need to be taken into account as well.  The cost of operating the analyzer should be pennies, not dollars, per day.

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Technical Issues

     The chemistry of the water is an important item to consider when choosing a chlorine analyzer.  How high of a chlorine residual to you need to read?  How dirty is the water?  What are the temperature, pH and alkalinity levels?  If you need to read chlorine levels higher than 4.0 ppm, the colormetric and probe style analyzers do not read high chlorine residuals.  Probe style analyzers, which do not usually require a buffer, do not operate well in warm water and pH levels higher than 8.0 pH.  Furthermore, these analyzers do not operate very well in dirty water applications as they require a steady pH level in order to provide a reliable reading of the chlorine level.

     These environments require analyzers that use a buffering agent.  The buffering agent compensates for pH levels.  Analyzers using buffering agents are not subject to temperature and dirty water fluctuations that may affect the reading of chlorine levels.  Always be certain that the selected analyzer will work with the chemistry of your water sample.

Control

     Is your analyzer being used to monitor, to control or to do both?  If a chlorine analyzer is being used solely as a monitor than most analyzers of the market would do the job.  If the chlorine analyzer is being used to control, however, not just any piece of equipment will do.  The way in which the analyzer reads the chlorine in its system should be considered.  Does the analyzer sample water over time or continuously?

Some analyzers use a "sample & hold method testing, which does not provide a true "on-line" output signal.  It takes a test every 2.5 minutes, changes the output signal to reflect any changes in residual, and holds that signal for 2.5 minutes until the results of the next sample test.  This produces a "staircase" type of output signal.  Compound Loop Controllers and Setpoint Control Programs are designed to see a continuously changing signal and respond better to a true "on-line" analyzer output.  Particularly in process control streams where residuals are apt to change rapidly.  In some cases, a staircase control signal can cause a controller to go into a reset mode.  This can sometimes be compensated for by using input filtering, but may slow response too much in short interval process streams.

Dependability

     The life expectancy of an analyzer should be at least 10 years.  Take a look at the manufacturer of the analyzer to see if they change their product from year to year.  Often frequent design changes, especially on the highly sophisticated models, are attempts to correct defects or deficiencies.  These high end models are not only expensive but their life expectancies are relatively short.  Operating a chlorine analyzer should not take a lot of time.  Weekly calibration checks and annual preventive maintenance should be all that is required.

Ease of Use

Operating the chlorine analyzer should be easy for your personnel.  If an electronic engineer is required to read the instruction manual and operate the analyzer, you should be looking elsewhere.

     In summary, just because an analyzer is the top of the line or the least expensive, does not mean that it will function well for your particular application.  If you are experiencing problems with your current system or if you are considering purchasing a new system, perhaps for the first time, the Foxcroft technical department stands ready to assist you.  Helping you choose the right chlorine analyzer is what we do best.