Myron L 9PTK with FCE Free Chlorine - Manual (Page 71)

67
same reference is used for both the pH and the ORP sensors. Both
pH and ORP will indicate 0 for a neutral solution. Calibration at zero
compensates for error in the reference junction.
A zero calibration solution for ORP is not practical, so the Ultrameter III
uses the offset value determined during calibration to 7 in pH calibration
(pH 7 = 0 mV). Sensitivity of the ORP surface is fixed, so there is no gain
adjustment either.
5. Sources of Error
The basics are presented in pH and ORP/Free Chlorine, pg. 64, because
sources of error are much the same as for pH. The junction side is the
same, and though the platinum surface will not break like the glass pH
surface, its protective glass sleeve can be broken. A surface film will
slow the response time and diminish sensitivity. It can be cleaned off
with detergent or acid, as with the pH glass.
C. Free Chlorine
1. Free Chlorine as an Indicator
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. Free Chlorine Units
The 9P 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 samples 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