CASCADIAN^®
Professional Water Treatment Products

O₃ Water Systems, Inc.
17700 147th St SE
Suite F
Monroe, WA 98272
USA

Phone: 360-794-9511
Fax: 360-794-0856

General Conductivity Theory

Conductivity is defined as the ability of a substance to conduct electric current, which is the reciprocal of resistivity. All substances posses conductivity to some degree, but the amount varies widely, ranging from extremely low (insulators such as glass or benzene) to very high (silver, copper, and metals in general). Most industrial interest is in measuring the conductivity of liquids, which generally consist of ionic compounds dissolved in water. These solutions have conductivity’s midway between insulators and conductors, which can be measured quite easily by electronic means. This offers a simple test which can tell much about the quality of water, or the make up of a solution. The basic unit of resistance measurement is the ohm, and the basic unit of conductivity measurement is the siemens. Conductivity is the conductance as measured between opposite faces of a 1 cm cube of a given material. This measurement is in units of siemens/cm. For most solutions this unit of measure is much too large and either m S/cm or mS/cm are used instead. The corresponding terms for specific resistivity are ohm-cm, Kohm-cm and Mohm-cm. Generally users of ultra pure water prefer to use resistivity units of Mohm-cm or Kohm-cm, because measurement in this unit tends to spread the scale out into the range of interest. In these applications, the use of conductivity has the advantage of an almost direct relationship with impurities, especially at low concentrations. Hence, a rising conductivity reading shows increasing impurities in the given solution. The draw back to conductivity is that it is a non-specific measurement; it cannot distinguish between various types of ions and the reading is proportional to the combined effect of all ions present. Because of this, under certain circumstances it may be necessary for a through analysis of a given solution to be made. In conclusion, conductivity offers a fast, reliable, and an in-expensive means of measuring the ionic content of a solution, with a high degree of accuracy and repeatability.