Rotary viscometers are cheap, convenient and practical, and are widely welcomed by users. Rotary viscometers are widely used to measure the dynamic viscosity of various fluids such as grease, paint, paint, plastics, food, medicine, adhesives and so on. The performance of our calibrated rotary viscometer is better than the requirements of the national metrological verification regulations. Especially the testers of small and medium-sized enterprises have many problems in the process of use, and the users have great data deviations when testing samples. Now how to analyze the accurate and reliable measurement results is as follows:
1. The rotary viscometer must be periodically verified. If necessary (the instrument is used frequently or in a critical state of qualification), an intermediate self-examination is required to determine its measurement performance. The coefficient error is within the allowable range, otherwise accurate data cannot be obtained.
2. Pay special attention to the temperature of the measured liquid. Many users ignore this point and think that the temperature difference does not matter. Our experiments prove that when the temperature deviation is 0.5 â„ƒ, some liquids have a viscosity value deviation of more than 5%. The temperature deviation has a great influence on the viscosity. The temperature increases and the viscosity decreases. So pay special attention to keep the temperature of the measured liquid constant near the specified temperature point, it is best not to exceed 0.1 â„ƒ for accurate measurement.
3. Selection of measuring container (outer cylinder). For the double-cylinder rotary viscometer, carefully read the instrument manual, different rotors (inner cylinder) match the corresponding outer cylinder, otherwise the measurement results will be huge deviation. For a single-cylinder rotary viscometer, in principle, the radius of the outer cylinder is infinitely large, and the actual diameter of the outer cylinder, that is, the measuring container, is not less than a certain size during actual measurement. Experiments show that especially when using the No. 1 rotor, if the inner diameter of the container is too small, it will cause a large measurement error.
4. Correctly select the rotor or adjust the speed so that the displayed value is between 20 ~ 90 divisions.
This type of instrument uses a dial and a pointer to read. Its stability and reading deviation are combined with 0.5 grids. If the reading is too small, such as near 5 grids, the relative error caused is more than 10%. If you choose a suitable rotor or speed If the reading is at 50 divisions, the relative error can be reduced to 1%. If the indicated value is more than 90 divisions, the torque generated by the balance spring is too large, and it is easy to produce creep and damage the balance spring, so the rotor and speed must be selected correctly.
5. Frequency correction. For the nominal frequency of domestic instruments is 50Hz, and China's current power supply frequency is also 50Hz, we use a frequency meter to test the variability is less than 0.5%, so the general measurement does not require frequency correction. However, for some instruments in Japan, Europe and the United States, the nominal frequency is 60Hz, frequency correction must be carried out, otherwise an error of 20% will be generated, and the correction formula is:
Actual viscosity = indicated viscosity Ã— nominal frequency Ã· actual frequency
6. The depth of the rotor immersed in the liquid and the influence of bubbles.
The rotational viscometer has strict requirements on the depth of the rotor immersed in the liquid, and must be operated according to the instructions (some double-barrel instruments have strict requirements on the amount of liquid tested, which must be measured with a measuring cylinder). The rotor is often immersed in the liquid with bubbles, and most of them will float up and disappear after a period of rotation of the rotor. The bubbles attached to the lower part of the rotor may sometimes not be eliminated. The presence of bubbles will cause large deviations in the measurement data, so tilt Immersing the rotor slowly is an effective method.
7. Cleaning of the rotor. The rotor (including the outer cylinder) used for measurement should be clean and free of dirt. Generally, it should be cleaned in time after the measurement, especially after the measurement of paint and adhesive. Pay attention to the cleaning method, soak it with a suitable organic solvent, and never use hard scrapers such as metal knives, because there will be deviations in the measurement results when there are serious scratches on the rotor surface.
8. Other issues needing attention.
1. Most instruments need to adjust the level, pay attention to the level problem at any time after replacing the rotor and adjusting the rotor height, and during the measurement process, otherwise it will cause reading deviation or even unable to read.
2. Some instruments need to be equipped with a protective frame, read the instructions carefully and install according to the regulations, otherwise it will cause the reading deviation.
3. Determine whether it is an approximate Newtonian fluid. For non-Newtonian fluids, the rotor, speed, and rotation time should be specified after selection, so as not to misunderstand the instrument.
In summary, although the structure of the rotary viscometer is simple and easy to use, if it is not used correctly, a certified instrument cannot obtain accurate measurement results, which affects the quality of the product.
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