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The measurement unit of resistance is the ohm.  The inverse of resistance is conductance and its basic unit of measurement is the mho (international system of units for mho is Siemens [S]).

The resistance of a conductor is inversely proportional to its cross sectional area and directly proportional to its length.  In the measurement of aqueous solution, conductivity is based on the reciprocal of the resistance of a 1ˉcm cube of material measured between opposite faces.  This configuration would be a cell with a constant of 1.

Conductivity cells usually consist of two metallic plates of a determined size mounted in a defined area.  The cell constant “K” is the length “L” (or distance between the plates) of the conducting path in centimeters divided by the effective cross sectional area “A” of the conducting path in square centimeters (K=L/A).

Amber Science instruments are designed to use a cell with a constant of 10 cmˉ¹.

Conduction in aqueous solutions is by ionic movement and increases with temperature.  This change is expressed in percent per degree Celsius relative to 25°C and is called the slope of the solution.

Amber Science instruments have Automatic Temperature Compensation (ATC) for slope correction.

The Total Dissolved Solids (TDS) in an aqueous solution that provides conduction is not temperature sensitive as is the conductivity.  By multiplying conductivity by an empirical factor, TDS may be displayed.  This empirical factor is determined by the components and temperature of the solution.  When the conductivity has been corrected to 25 degrees C, this factor is usually between 0.5 and 0.7. 

Amber Science conductivity instruments meet the requirements for the determination of electrical conductivity of water under ASTM method D 1125.  For additional information about conductivity determinations and methods, the following books and journals listed below are recommended.

References for Conductivity


Annual Book of ASTM Standards 2000, Volume 11.01 Water (I), Revised Annually, ISBN 0-8031-2814-2, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428 Tel (610) 832-9500 Fax (610) 832-9555

Standard Methods for the Examination of Water and Wastewater, 20th Edition, ISBN 0-87553-235-7, Publication office, American Public Health Association, 1015 Fifteenth Street NW, Washington DC 20005-2605

Ultrapure Water, The Definitive Journal of High-Purity Water, ISSN: 0747-8291, Tall Oaks Publishing, Inc., 60 Golden Eagle Lane, Littleton, CO 80127, Tel # (303) 973-6700 Fax# (303) 973-5327

International Standard 7888, Ref. No. ISO 7888-1985 (E), Water quality - Determination of electrical conductivity, 6 pages, International Organization for Standardization, Reproduced by Global Engineering Documents, 15 Inverness Way East, Englewood, CO 80112, Tel# (800) 854-7179 Fax# (303) 790-0730

Approximate Conductivity measurements:
High Purity Water .056 micro Siemens/cm @ 25°
Distilled Water .5 micro Siemens/cm @ 25°
Good Tap Water 50 micro Siemens/cm @ 25°
Max Potable Water 1500 micro Siemens/cm @ 25°
Ocean Water 53,000 micro Siemens/cm @ 25°