Myron L 9PTK - Manual (Page 63)

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E. Other Solutions
A salt solution like seawater or liquid fertilizer acts like NaCl. An internal
correction for NaCl can be selected for greatest accuracy with such
solutions. Many solutions are not at all similar to KCl, NaCl or 442. A
sugar solution, or a silicate, or a calcium salt at a high or low temperature
may require a “User” value peculiar to the application to provide readings
close to the true compensated conductivity.
Clearly, the solution characteristics should be chosen to truly represent
the actual water under test for rated accuracy of ±1%. Many industrial
applications have historically used relative measurements seeking a
number to indicate a certain setpoint or minimum concentration or trend.
The Ultrameter III gives the user the capability to collect data in “KCl
conductivity units” to compare to older published data, in terms of NaCl
or 442, or as appropriate. The Ultrameter III can be used to reconcile
data taken with other compensation assumptions, especially with its
ability to allow custom characteristics through the User mode.
XXi. cOnDUctivity cOnversiOn to tOtal DissOlveD
sOliDs (tDs)
Electrical conductivity indicates solution concentration and ionization
of the dissolved material. Since temperature greatly affects ionization,
conductivity measurements are temperature dependent and are
normally corrected to read what they would be at 25°C (ref. Temperature
Compensation, pg. 56).
A. How it’s Done
Once the effect of temperature is removed, the compensated conductivity
is a function of the concentration (TDS). Temperature compensation of
the conductivity of a solution is performed automatically by the internal
processor with data derived from chemical tables. Any dissolved salt at
a known temperature has a known ratio of conductivity to concentration.
Tables of conversion ratios referenced to 25°C have been published by
chemists for decades.
B. Solution Characteristics
Real world applications have to measure a wide range of materials and
mixtures of electrolyte solutions. To address this problem, industrial users
commonly use the characteristics of a standard material as a model for
their solution, such as KCl, which is favored by chemists for its stability.
Users dealing with seawater, etc., use NaCl as the model for their
concentration calculations. Users dealing with freshwater work with
mixtures including sulfates, carbonates and chlorides, the three
predominant components (anions) in freshwater that the Myron L