Myron L 6PFCE and 4P - Manual (Page 51)

C. Free Chlorine
1. Free Chlorine as an Indicator of Sanitizing Strength
Chlorine, which kills bacteria by way of its power as an oxidizing agent,
is the most popular germicide used in water treatment. Chlorine is
not only used as a primary disinfectant, but also to establish a
sufficient residual level of Free Available Chlorine (FAC) for ongoing
disinfection.
FAC is the chlorine that remains after a certain amount is consumed by
killing bacteria or reacting with other organic (ammonia, fecal matter) or
inorganic (metals, dissolved CO
2
, Carbonates, etc) chemicals in solution.
Measuring the amount of residual free chlorine in treated water is a well
accepted method for determining its effectiveness in microbial control.
The Myron L Company FC E method for measuring residual disinfecting
power is based on ORP, the specific chemical attribute of chlorine (and
other oxidizing germicides) that kills bacteria and microbes.
2. FC E Free Chlorine Units
The 6PIIFC E is the first handheld device to detect free chlorine directly,
by measuring ORP. The ORP value is converted to a concentration
reading (ppm) using a conversion table developed by Myron L Company
through a series of experiments that precisely controlled chlorine levels
and excluded interferants.
Other test methods typically rely on the user visually or digitally
interpreting a color change resulting from an added reagent-dye. The
reagent used radically alters the sample’s pH and converts the various
chlorine species present into a single, easily measured species. This
ignores the effect of changing pH on free chlorine effectiveness and
disregards the fact that some chlorine species are better or worse
sanitizers than others.
The Myron L Company 6PIIFC E avoids these pitfalls. The chemistry of
the test sample is left unchanged from the source water. It accounts for
the effect of pH on chlorine effectiveness by including pH in its calculation.
For these reasons, the Ultrameter II’s FC E feature provides the best
reading-to-reading picture of the rise and fall in sanitizing effectivity of
free available chlorine.
The 6PIIFC E also avoids a common undesirable characteristic of other
ORP-based methods by including a unique Predictive ORP value in its
FC E calculation. This feature, based on a proprietary model for ORP
sensor behavior, calculates a final stabilized ORP value in 1 to 2 minutes
rather than the 10 to 15 minutes or more that is typically required for an
ORP measurement.
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