Generally speaking, the conductivity of aqueous solution is directly proportional to the concentration of dissolved solids, that is, the higher the concentration of solids, the greater the conductivity.
Therefore, the relationship between conductivity and dissolved solid concentration can be approximately expressed as 1.4μS/cm=1ppm or 2μS/cm=1ppm (per million units of CaCO3).
The total hardness of water can be obtained indirectly by using conductivity meter or total solid solubility meter. For the convenience of approximate conversion, the conductivity of 1μs/cm =0.5 PPM hardness.
Electrical conductivity is the ability of material to transmit current, relative to the resistance value, the unit is Siemens/cm (S/cm), 10-6 of the unit is expressed in μS/cm, 10-3 in mS/cm.
Note:
1. The theoretical error of indirect measurement of water hardness by conductivity is about 20-30ppm;
2. The conductivity of solution determines the movement of molecules, and the temperature affects the movement of molecules. In order to compare the measurement results, the test temperature is generally set at 20℃ or 25℃;
3. More accurate hardness value of water can be obtained by reagent testing.
The electrical conductivity of water is related to the amount of inorganic acid, alkali and salt. When their concentration is low, the conductivity increases with increasing concentration, so this indicator is often used to predict the total concentration of ions or salinity in water.
Different types of water have different electrical conductivity. The conductivity of fresh distilled water is 0.2-2μS /cm, but after a period of time, due to the absorption of CO2, it will increase to 2-4 μS/cm; The conductivity of ultra-pure water is less than 0.10/μS/cm. The conductivity of natural water is mostly between 50-500 μS/cm, and that of mineralized water is up to 500-1000 μS/cm. The electrical conductivity of industrial wastewater containing acid, alkali and salt often exceeds 10000μS/cm; The conductivity of seawater is about 30,000 μS/cm.