The concept of conductivity meter and its measurement principle

Conductivity is the ability of an object to conduct current. The measurement principle of the conductivity meter is to put two parallel plates into the solution to be tested, add a certain potential (usually a sine wave voltage) to both ends of the plate, and then measure the flow between the plates. Current. According to Ohm's law, the conductivity (G) - the reciprocal of the resistance (R), is determined by the conductor itself. The basic unit of conductivity is Siemens (S), originally known as ohms. Since the geometry of the conductivity cell affects the conductivity value, the standard measurement is expressed in terms of unit conductivity S/cm to compensate for differences in various electrode sizes. The unit conductivity (C) is simply the product of the measured conductivity (G) and the cell constant (L/A). Here L is the length of the liquid column between the two plates, and A is the area of ​​the plate. .

The conductivity of the aqueous solution is directly proportional to the concentration of dissolved solids, and the higher the concentration of solids, the greater the conductivity. The relationship between the conductivity and the dissolved solids concentration is approximately expressed as: 1.4 μS/cm = 1 ppm or 2 μS/cm = 1 ppm (per million units of CaCO3). The total hardness value of water can be indirectly obtained by using a conductivity meter or a total solids dissolution meter. As described above, for a convenient conversion, 1 μs/cm conductivity = 0.5 ppm hardness. Conductivity is the ability of a substance to deliver a current, as opposed to the resistance value, in units of Siemens/cm (S/cm), 10-6 of the unit is expressed in μS/cm, and 10-3 is expressed in mS/cm. But need to pay attention to: (1) indirectly measure the hardness of water with conductivity, the theoretical error is about 20-30ppm. (2) The conductivity of the solution determines the movement of the molecule, and the temperature affects the movement of the molecule. In order to compare the measurement results, the test temperature is generally It is determined to be 20 ° C or 25 ° C (3) using reagent testing to obtain a more accurate water hardness value.

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