Detailed explanation of the working principle of the conductivity tester

Conductivity tester
The conductivity tester is a high-end water quality management and automation for medical multi-effect distilled water systems, boiler bottom water, condensate water, heat exchange systems, industrial heat cleaning of mechanical parts, industrial circulating water, etc. operating in higher temperature environments A wide temperature range online water quality analysis instrument developed for control.

Chinese online conductivity meter is a new generation of all-Chinese microcomputer-based instruments, with full Chinese display, Chinese menu operation, full intelligence, multi-function, high measurement performance, strong environmental adaptability and other characteristics. The secondary meter is equipped with an electrode with a constant of 1.0 or 10 to measure the conductivity of general liquids; equipped with an electrode of 0.1 or 0.01, it can accurately measure the conductivity of pure water or ultrapure water, especially suitable for power plant boiler feed water and steam condensation Online continuous monitoring of the conductivity of high-purity water such as water.

Conductivity controllers such as pen type BCNSCAN10/20/30, portable BEC520, BEC530, BEC531, BEC540, laboratory benchtop BEC950, BEC110, BEC120, BEC307 and online BEC200A, BEC200B, BEC200D, BEC200E, BEC200F, BEC210 are widely used in Industry, power, agriculture, medicine, food, scientific research and environmental protection. This instrument is also a necessary inspection equipment for QS and HACCP in food factories and drinking water factories.

The working principle of the conductivity tester is explained in detail

The measuring principle of the conductivity meter

The measuring principle of the conductivity measuring instrument is to put 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 flow between the plates Current. According to Ohm's law, conductivity (G)-the reciprocal of resistance (R) 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 the standard measurement to compensate for the difference 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 the aqueous solution is directly proportional to the dissolved solids concentration, 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 value of water can be obtained indirectly 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. It is relative to the resistance value. The unit is Siemens/cm (S/cm). The unit of 10-6 is expressed in μS/cm, and when it is 10-3, it is expressed in mS/cm. However, please note: (1) Indirect measurement of water hardness by conductivity, the theoretical error 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 it as 20°C or 25°C (3) Reagent testing can obtain a more accurate water hardness value.

The conductivity of water has a certain relationship with the amount of inorganic acid, alkali and salt contained in it. When their concentration is low, the conductivity increases as the concentration increases. Therefore, this indicator is often used to estimate the total concentration of ions or salt content in water. Different types of water have different 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 increases to 2-4μS/cm; the conductivity of ultrapure water is less than 0.10/μS/cm; the conductivity of natural water is more Between 50-500μS/cm, mineralized water can reach 500-1000μS/cm; the conductivity of industrial wastewater containing acid, alkali, and salt often exceeds 10,000μS/cm; the conductivity of seawater is about 30,000μS/cm.

The electrode constant is often measured with a standard potassium chloride solution of known conductivity. The conductivity (25℃) of different concentrations of potassium chloride solution is listed in the table below. The conductivity of the solution is related to its temperature, the polarization phenomenon on the electrode, the distributed capacitance of the electrode and other factors. Generally, compensation or elimination measures are adopted on the instrument.

The water sample should be measured as soon as possible after collection. If it contains coarse suspended matter, oil and grease, which interferes with the measurement, it should be filtered or removed by extraction.

1) First immerse the platinum black electrode in deionized water for several minutes.

2) Adjust the meter head screw M so that the pointer points to the zero point.

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

4) After turning on the power switch K to warm up for a few minutes, adjust the correction regulator Rw3 to make the pointer on the full scale.

5) Move the high-cycle and low-cycle switches K3 to the appropriate gear.

6) Move the range selection switch R1 to the appropriate gear.

7) Adjust the electrode constant regulator Rw2 to correspond 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 equal to the conductivity of the solution).

8) After washing the electrode with a small amount of the solution to be tested, insert its 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, pull the calibration and measurement switch K2 to the measurement position. Read the indicator of the meter needle and multiply it by the multiple indicated by the range selection switch R1 to obtain the conductivity of this solution. Repeat the measurement and take the average value.

10) Turn the calibration and measurement switch K2 to the "calibration" position, and take out the electrode.

11) After the measurement is completed, disconnect the power supply. After the electrode is shaken and washed with deionized water, it is immersed in deionized water for use.