Introduction to the use of conductivity tester

The conductivity tester is a multi-range instrument that can meet the testing requirements of a variety of applications from deionized water to seawater. This instrument can provide automatic temperature compensation and set a temperature coefficient, so it can be used to measure liquid samples with a temperature coefficient different from that of water. It can provide three ranges and has an automatic range selection function, which can automatically select the appropriate range during detection.

A dual-plug stainless steel conductivity electrode with built-in temperature sensor (used for automatic temperature compensation), a rubber non-slip sleeve, 4 alkaline AAA batteries, instrument operation manual and a portable soft case are provided with the instrument.

Introduction to the use of conductivity tester

One, the concept of conductivity meter
Conductivity: The conductivity of water is the reciprocal of the resistance of water, and it is usually used to express the purity of water. Conductivity is the ability of an object to conduct current. 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 voltage and current.

2. The unit of the conductivity meter
The basic unit of conductance is Siemens (S), originally called mho, which means the reciprocal of the resistance unit ohm. Because the geometry of the conductivity cell affects the conductivity value, the unit S/cm is used to express the conductivity 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. =ρl=l/σ

(1) Definition or explanation The reciprocal of resistivity is conductivity. σ=1/ρ;

(2) Unit: In the International System of Units, the unit of conductivity is Siemens/meter, and other units are: s/cm, us/cm. 1S/m=0.01s/cm=10000us/cm=1000ms/m=1000000us/m; (3) Explain that the physical meaning of electrical conductivity is the performance of a substance to conduct electricity. The greater the conductivity, the stronger the conductivity, and vice versa.

Introduction to the use of conductivity tester

Three, the measurement principle of conductivity
The electric field that causes the ions to move in the measured solution is generated by the two electrodes that are in direct contact with the solution. The pair of measuring electrodes must be made of chemical resistant materials. In practice, materials such as titanium are often used. The measuring electrode composed of two electrodes is called the Kohlrausch electrode.

Conductivity measurement needs to clarify two aspects. One is the conductivity of the solution, and the other is the geometric relationship of 1/A in the solution. The conductivity can be obtained by measuring current and voltage. This measurement principle is applied in today's direct display measuring instruments. And K = L /A

A——The effective plate of the measuring electrode

L——The distance between the two plates

The value of 　　 is called the cell constant. In the presence of a uniform electric field between the electrodes, the electrode constant can be calculated by geometric dimensions. When two square plates with an area of 1 cm2 are separated by 1 cm to form an electrode, the constant K of this electrode is 1 cm-1. If the conductivity value G=1000μS measured with this pair of electrodes, then the conductivity of the tested solution K=1000μS/cm.

Under normal circumstances, the electrode often forms a partial non-uniform electric field. At this time, the cell constant must be determined with a standard solution. Standard solutions generally use KCl solution. This is because the conductivity of KCl is very stable and accurate under different temperatures and concentrations. The conductivity of 0.1 mol/l KCl solution at 25°C is 12.88mS/CM. The so-called non-uniform electric field (also called stray field, leakage field) has no constant, but is related to the type and concentration of ions. Therefore, a pure stray field electrode is a bad electrode, and it cannot meet the needs of a wide measurement range through calibration. three. How to use conductivity

Many users know how to use the PH meter, but for the conductivity meter, some users and friends have consulted our engineers. Let me share with you how to use the conductivity meter. 1. Before turning on the power switch, observe whether the needle is pointing to zero, and adjust the screw on the meter head to make the needle point to zero. 2. Move the calibration measurement switch to the "calibration" position.

3. Plug in the power cord, turn on the power switch, and warm up for a few minutes (until the pointer is completely stabilized) and adjust the "adjustment" regulator to make the meter indicate full scale.

4. When using (1)-(8) range to measure the liquid whose conductivity is lower than 300μS.cm-1, select "low cycle", then move the high/low cycle switch to the low cycle. When using the (9)-(10) range to measure the liquid whose conductivity is in the range of 300μS.cm-1 to 105μS.cm-1, turn to the "high cycle".

5. Set the range selection switch to the required measurement range. If the conductivity of the solution to be measured is unknown beforehand, it should be set to the conductivity measurement range first, and then gradually decrease to prevent the needle from bending. 6. The use of the electrode: When using the electrode clamp, clamp the bakelite cap of the electrode, and fix the electrode clamp on the electrode rod. (1) When the conductivity of the tested solution is lower than 0.3μS.cm-1, use the DJS-0.1 electrode, then the "electrode constant compensation adjuster" should be adjusted to the position of 10 times the supporting electrode constant: for example If the supporting electrode constant is 0.090, it should be adjusted to the 0.90 position. (2) When the conductivity of the tested solution is lower than 10μS.cm-1, use DJS-0.1 type electrode, then the "electrode constant compensation adjuster" should be adjusted at the corresponding position of the matched electrode constant: for example, supporting If the electrode constant is 0.95, it should be adjusted to the 0.95 position, and if the supporting electrode constant is 1.1, it should be adjusted to the 1.1 position.

7. Insert the electrode plug into the electrode socket, tighten the fastening screw on the socket, and then put the electrode into the solution to be tested.

8. Then calibrate [when measuring with (1)-(8) range, adjust to low cycle when calibrating, when using (9)-(12) measuring range, adjust to high cycle], switch to "calibration" ", adjust the correction regulator to make the indication at full scale.

9. When using (0-0.1) or (0-0.3) μS.cm-1 to measure high-purity water, first insert the electrode lead into the electrode socket, before the electrode is filled with solution, adjust the capacitance compensation regulator to The meter is indicated as a value (this value is the leakage resistance between the platinum plates of the electrodes. Due to the existence of this leakage resistance, the meter pointer cannot reach zero when the capacitance compensation regulator is adjusted).

3. What types of conductivity electrodes are there in the conductivity meter? What are the different uses? Conductivity electrodes are generally divided into two types: two-electrode type and multi-electrode type.

1. Two-electrode conductivity electrode. The two-electrode conductivity electrode is currently the most widely used type of conductivity electrode in China. The structure of the experimental two-electrode conductivity electrode is to sinter two platinum sheets on two parallel glass sheets or the inner wall of a circular glass tube to adjust the platinum sheet Area and distance can be made into conductivity electrodes with different constant values. Usually there are K=1, K=5, K=10 and other types. The two-electrode conductivity electrode used on the online conductivity meter is often made into a cylindrical symmetrical electrode. When K=1, graphite is often used. When K=0.1, 0.01, the material can be stainless steel or titanium alloy.

2. Multi-electrode conductivity electrode. Multi-electrode type conductivity electrodes generally have several ring-shaped electrodes on the support. Through different combinations of ring-shaped electrodes in series and parallel, conductivity electrodes with different constants can be made. The material of the ring electrode can be graphite, stainless steel, titanium alloy and platinum.

3. There are four-electrode type and electromagnetic type for conductivity electrode. The advantage of the four-electrode conductivity electrode is that it can avoid the measurement error caused by electrode polarization, and it is more used in foreign experimental and online conductivity meters. The characteristic of electromagnetic conductivity electrode is that it is suitable for measuring high-conductivity solutions. It is generally used in industrial conductivity meters, or uses its measuring principle to make single-component concentration meters, such as hydrochloric acid concentration meters and nitric acid concentration meters. four. How to determine the conductivity cell constant? Why calibrate the constant?

"According to the formula K=S/G, the cell constant K can be obtained by measuring the conductance G of the conductivity electrode in a certain concentration of KCL solution. At this time, the conductivity S of the KCL solution is known. Because the concentration and temperature of the measuring solution are different, and the accuracy and frequency of the measuring instrument are also different, the conductivity cell constant K sometimes has a large error. After a period of use, the cell constant may also change. Therefore, the newly purchased conductivity For the electrode and the conductivity electrode after a period of use, the electrode constant should be re-measured and calibrated to judge whether a conductivity electrode is good or bad, and the constant range is 0.8K "K "1.2K. The following points should be paid attention to when measuring the conductivity of the electrode constant: 1. When measuring, the supporting conductivity meter should be used instead of other types of conductivity meters. 2. The temperature of the KCL solution for measuring the cell constant should be close to the temperature of the actual measured solution. 3. The concentration of the KCL solution for measuring the cell constant should be close to the concentration of the actual measured solution.