Tips: Conductivity meter measurement method

　　The measuring principle of the conductivity meter is to place two parallel plates in the solution to be measured, add a certain potential (usually a sine wave voltage) to both ends of the plates, and then measure the current flowing between the plates. According to Ohm's law, conductivity (G) - the reciprocal of resistance (R) is determined by the conductor itself.

　　The basic unit of conductivity is the Siemens (S), formerly known as the Ohm. Because the geometry of the conductivity cell affects the conductivity value, the standard measurement uses the unit conductivity S/cm to compensate for the differences caused by various electrode sizes. The unit conductivity (C) is simply the product of the measured conductivity (G) and the conductivity cell constant (L/A). Here L is the length of the liquid column between the two plates, and A is the area of ​​the plates.

　　The conductivity of an aqueous solution is directly proportional to the concentration of dissolved solids, and the higher the solids concentration, the greater the conductivity. The relationship between conductivity and dissolved solids concentration is approximately expressed as: 1.4μS/cm=1ppm or 2μS/cm=1ppm (per million units of CaCO3).

　　The total hardness of water can be indirectly obtained by using a conductivity meter or a total dissolved solids meter. As mentioned above, for the convenience of approximate conversion, 1μs/cm conductivity = 0.5ppm hardness. Conductivity is the ability of a substance to transmit current, which is relative to resistance. The unit is Siemens/cm (S/cm). 10-6 of this unit is expressed as μS/cm, and 10-3 is expressed as mS/cm.

　　But please note:

　　(1) The theoretical error of indirectly measuring water hardness by conductivity is about 20-30ppm

　　(2) The conductivity of the 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) Reagent testing can obtain a more accurate water hardness value.