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   With the development of the times and the advancement of science and technology, viscometers have a certain share and potential in the current market. Viscometers are widely used to measure the dynamic viscosity of various fluids such as oils, paints, coatings, plastics, food, drugs, and adhesives.

After the rotational viscometer is turned on, the zero position must be detected first. This operation is generally carried out without installing the rotor, and then the inner cylinder of radius R2 is coaxially installed in the outer cylinder of radius R1, which is filled with viscous fluid. The synchronous motor Rotate at a stable speed, connect the scale discs one after another, and then drive the inner cylinder (ie the rotor) to rotate through the hairspring and the rotating shaft. The greater the torque generated by the counterbalance, the larger the scale indicated by the pointer on the dial. Multiply the reading by a specific factor to get the dynamic viscosity of the liquid.

According to the viscometer measurement principle, in order to obtain accurate and reliable measurement data, the following points must be paid attention to:

1. The performance indicators of the viscometer must meet the requirements of the national metrological verification regulations. The instrument in use should be checked periodically, and if necessary (the instrument is frequently used or in a critical state), an intermediate self-examination should be carried out to confirm that its measurement performance is qualified, and the coefficient error is within the allowable range, otherwise accurate data cannot be obtained.

Second, pay special attention to the temperature of the liquid to be measured. Many users ignore this point and think that the temperature difference does not matter. Our experiments have proved that when the temperature deviation of the viscometer is 0.5 ℃, the viscosity value of some liquids deviates by more than 5%, and the temperature deviation has a great influence on the viscosity. The temperature increases and the viscosity decreases. Therefore, special attention should be paid to keep the temperature of the liquid to be measured constant near the specified temperature point, and it is best not to exceed 0.1 °C for accurate measurement.

3. The choice of the measuring container (. For the double-cylinder rotational viscometer, read the instrument manual carefully. Different rotors (inner cylinders) match the corresponding outer cylinders, otherwise the measurement results will deviate greatly. For single-cylinder rotational viscometers, in principle The radius of the outer cylinder is required to be infinite, and the actual measurement requires that the inner diameter of the outer cylinder, that is, the measuring container, is not less than a certain size.

4. Correctly select the rotor or adjust the speed so that the indicated value is between 20 and 90 grids. This type of viscometer uses a dial and a pointer to read, and its stability and reading deviation are combined with 0.5 grids. If the reading is too small, such as around 5 grids, the relative error caused is more than 10%. If you choose a suitable rotor or rotating speed If the reading is at 50 divisions, the relative error can be reduced to 1%. If the indication value is above 90 grids, the torque generated by the hairspring will be too large, which will easily cause creep and damage the hairspring. Therefore, the rotor and speed must be selected correctly.

5. Frequency correction. The nominal frequency of domestic instruments is 50Hz, and the current power supply frequency in my country is also 50Hz. We use a frequency meter to test the variability of less than 0.5%, so the general measurement does not require frequency correction. However, for some instruments in Japan and Europe, the nominal frequency is 60Hz, and frequency correction must be performed, otherwise an error of 20% will occur.

The depth of rotor immersion in liquid and the effect of air bubbles. The rotational viscometer has strict requirements on the depth of the rotor immersed in the liquid, and must be operated in accordance with the requirements of the instructions (some dual-tube instruments have strict requirements on the amount of liquid tested, which must be measured with a graduated cylinder). When the rotor is immersed in the liquid, there are often bubbles, and most of them will float and disappear after the rotor rotates for a period of time. Sometimes the bubbles attached to the lower part of the rotor cannot be eliminated. Slowly immersing the rotor is an effective method.

Rotor cleaning. The rotor (including the outer cylinder) used for viscometer measurement should be clean and free of dirt. Generally, it should be cleaned in time after measurement, especially after measuring paint and adhesive. Pay attention to the cleaning method. It can be soaked in a suitable organic solvent. Never use a metal knife or other hard scraping, because serious scratches on the surface of the rotor will cause deviations in the measurement results.