The term Conductance refers to the readiness of materials to carry an electric current. Liquids which carry an electric current are generally referred to as electrolytic conductors. The flow of current through electrolytic conductors is accomplished by the movement of electric charges (positive and negative ions) when the liquid is under the influence of an electrical field. The conductance of a liquid can be defined by its electrical properties – the ratio of current to voltage between any two points within the liquid. As the two points move closer together or further apart, this value changes. To have useful meaning for analytical purposes, a dimension needs to be given to the measurement; i.e., the physical parameters of the measurement.
By defining the physical parameters of the measurement, a standard measure is created. This standard measure is referred to as specific conductance or conductivity.
It is defined as the reciprocal of the resistance in ohms, measured between the opposing faces of 1 cm cube of liquid at a specific temperature.
The units used to define conductance are:
1/ohm = 1 mho = 1000 mS = 1,000,000 uS.
S.I. units may be used in place of mhos;
1 mho = 1 Siemen (S).
Conductivity units are expressed as
µS/cm (1.0 dS/m = 1. 0 µS/cm) or mS/cm.
What is Conductivity ?
Conductivity is the ability of a material to conduct electric current. The principle by which instruments measure conductivity is simple – two plates are placed in the sample, a potential is applied across the plates (normally a sine wave voltage), and the current is measured. Conductivity (G), the inverse of resistivity (R) is determined from the voltage and current values according to Ohm’s law.
G = I/R = I (amps) / E (volts)