Conductivity meter measurement method

Introduction: Conductivity meter is a laboratory conductivity measuring instrument. In addition to measuring the conductivity of general liquids, it can also meet the needs of measuring the conductivity of high-purity water.
　　
　　The measurement principle of the conductivity meter is to place two parallel plates in the measured solution, add a certain potential (usually a sine wave voltage) at both ends of the plates, and then measure the current flowing between the plates. According to Ohm's law, conductivity (G) is the reciprocal of resistance (R), which is determined by the conductor itself.
　　
　　The basic unit of conductivity is Siemens (S), which was originally called Ohm. Because the geometry of the conductivity cell affects the conductivity value, the unit conductivity S/cm is used in standard measurements 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 aqueous solution is directly proportional to the concentration of dissolved solids, and the higher the solid 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 value of water can be indirectly obtained 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 electric current, which is relative to the resistance value. 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.
　　
　　However, it should be noted that:
　　
　　(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 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.