Conductivity is a well recognized, and sometimes indispensable, parameter of state-of-the-art water, wastewater and industrial process analysis. Continuous measuring systems are employed to monitor the salt load at the influent of wastewater treatment plants, to control quality of drinking water and ultra-pure water or to determine non-specific contaminants in industrial processes.

For almost 60 years, WTW has been one of the leading manufacturers of precision conductivity measurement systems, setting new standards with innovative sensor technology and fully evolved designs tailored to practical applications. WTW products meet the most stringent requirements set by industry for continuous on-line analysis instruments.

A special measuring transducer as well as sensors and accessories are available for use in explosion-proof areas (see brochure “Product Details”).

Conductivity as a summation parameter is a measure of the level of ion concentration of a solution. The more salts, acids or bases are dissociated, the greater the conductivity of the solution. In water or wastewater it is mainly a matter of the ions of dissolved salts, and consequently the conductivity is an index of the salt load in wastewater or, respectively, the purity of potable water. The measurement of conductivity is also widely used in industrial production, such as process control in food and pharmaceutical industries.

The measurement of conductivity is generally expressed in S/cm (or mS/cm) which is the product of the conductance of the test solution and the geometric factor of the measuring cell. The scale for aqueous solutions starts at a conductivity of 0.05 µS/cm (at 25 °C) for ultrapure water. The conductivity of natural waters, such as drinking water or surfacewater is typically in range of 100 - 1000 µS/cm. The upper End of the scale is reached by some acids and alkalis.

The conductivity of a solution is critically dependent on temperature. Therefore, the conductivity readings must be referred to a common reference temperature (25°C) for comparability. The term “temperature compensation” is used in the sense of a mathematical conversion; i.e. a measured conductivity (θ) at any given temperature to the corresponding conductivity value that would be taken at the reference temperature (25°C).

The conductivity of most aqueous solutions varies more or less linearly with temperature θ. In these cases, a linear correction function to compensate for the influence of temperature can be used. For example, the correction coefficient for sewage is approx. 2%/K.

WTW monitors automatically calculate the corrected conductivity values based on the selected temperature coefficient. For the compensation of natural water a non-linear function (nLF) (i.e., built-in table for natural water properties) is available.