Conductivity is the ability of an object to conduct current. The concept of conductivity meter and its measuring principle The measuring principle of the conductivity meter is to put two parallel plates into the solution to be measured, and add a certain potential (usually a sine wave voltage) at both ends of the plate. , Then measure the current flowing between the plates. According to Ohm's law, the conductivity (G), the inverse of the resistance (R), is determined by the conductor itself. The basic unit of conductivity is Siemens (S), originally known as ohms. Because 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 the difference in electrode size. 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 two plates, and A is the area of ​​the plate .

The conductivity of the aqueous solution is directly proportional to the dissolved solids concentration, and the higher the solids concentration, the higher the conductivity. Conductivity meter concept and its measurement principle The relationship between conductivity and 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 obtained indirectly by using a conductivity meter or a total solid dissolution meter. As described above, in order to approximate the conversion convenience, 1 μs/cm conductivity=0.5 ppm hardness. Conductivity is the ability of a substance to carry an electrical current and is in terms of resistance, in Siemens/cm (S/cm). The unit of 10-6 is expressed in μS/cm and in 10-3 it is expressed in mS/cm. However, it should be noted that: (1) The water hardness is indirectly measured by the conductivity. The theoretical error is about 20-30ppm. (2) The conductivity of the solution determines the movement of the molecules, and the temperature affects the movement of the molecules. To compare the measurement results, the test temperature is generally Set to 20 °C or 25 °C (3) using reagent testing can get more accurate water hardness value.

The conductivity of water is related to the amount of inorganic acids, alkalis and salts it contains. When their concentrations are low, the conductivity increases as the concentration increases. Therefore, this index is often used to estimate the total concentration or salt content of ions in water. The concept of a conductivity meter and its measuring principle Different types of water have different electrical conductivity. The conductivity of fresh distilled water is 0.2-2μS/cm, but after standing for a while, due to absorption of CO2, it increases to 2-4μS/cm; the conductivity of ultrapure water is less than 0.10/μS/cm; the conductivity of natural water is much In 50-500μS/cm, the mineralized water can reach 500-1000μS/cm; the conductivity of industrial wastewater containing acid, alkali and salt often exceeds 10000μS/cm; the conductivity of seawater is approximately 30000μS/cm. The electrode constant is often determined using a standard potassium chloride solution of known conductivity. The conductivity of different concentrations of potassium chloride solution (25°C) is listed in the table below. The conductivity of a solution is related to its temperature, the polarization on the electrode, and the capacitance of the electrode. The instrument is generally compensated or eliminated.

The water sample should be determined as soon as possible after collection. The concept and measurement principle of the conductivity meter, such as containing large suspended solids, oil and fat, should be determined by interference and should be filtered or extracted.

1) Immerse the platinum black electrode in deionized water for a few minutes.

2) Adjust the head screw M so that the pointer points at zero.

3) Turn the calibration and measurement switch K2 to the "correction" position.

4) After turning on the power switch K and warming up for a few minutes, adjust the correction regulator Rw3 so that the pointer is at full scale.

5) Turn the high- and low-cycle switch K3 to the proper position.

6) Move the range selector switch R1 to the proper position.

7) Adjust the electrode constant regulator Rw2 so that it corresponds to the constant of the electrode used (this is equivalent to adjusting the electrode constant to 1 and the measured conductivity of the solution is numerically equivalent to the conductance of the solution). 8) After flushing the electrode with a small amount of the test solution, insert the plug into the electrode socket Kx and immerse it in the solution to be tested.

9) After adjusting the calibration regulator Rw3 to full scale, turn the calibration and measurement switch K2 to the measurement position. Read the indicator number of the hands, multiply the multiple of the range selection switch R1, that is, the conductivity of the solution. Repeat the measurement once and take the average value.

10) Put the calibration and measurement switch K2 to the “correction” position and take out the electrode.

11) After the measurement is completed, disconnect the power supply. The electrode was rinsed with deionized water and immersed in deionized water for later use. The concept of conductivity meter and its measuring principle