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Viscometer in the use of the process to be aware of several issues

更新时间:2017-04-20 10:36:54点击次数:1805次字号:T|T
Rotational viscometer is widely used in the determination of oil, paint, paint, plastics, food, drugs, adhesives and other dynamic viscosity of the fluid. The instrument is simple, cheap, convenient and practical, and thus popular. In the long process of
Rotational viscometer is widely used in the determination of oil, paint, paint, plastics, food, drugs, adhesives and other dynamic viscosity of the fluid. The instrument is simple, cheap, convenient and practical, and thus popular. In the long process of testing the instrument, we found that many users, especially small and medium-sized enterprise test personnel in the course of the existence of many problems, often we test the performance of the instrument is better than the requirements of national measurement procedures, but the user in the test sample When the data deviation is very large. Now on how to correctly use this type of instrument to obtain accurate and reliable measurement results are as follows.

First of all, a brief introduction to the measurement of the instrument principle:
After the start of the rotary viscometer, it is necessary to first detect the zero position. This operation is normally carried out without the installation of the rotor. Then, the inner cylinder of the radius R2 is coaxially mounted in the outer cylinder of the radius R1, which is filled with viscous fluid, To rotate at a steady speed, successive discs, and then through the hairspring and shaft to drive the inner cylinder that is the rotor rotation, the inner tube that is the role of fluid-based viscous moments, the greater the role of the gossamer to compete with the resulting The greater the torque, so the pointer on the dial indicates the greater the scale. Multiplying the reading by a specific coefficient yields the dynamic viscosity of the liquid.

According to its measurement principle, in order to obtain accurate and reliable measurement data must pay attention to the following points:
First, the performance of the instrument must meet the requirements of the national measurement procedures. In the use of the instrument to carry out periodic testing, if necessary (the instrument used frequently or in a critical state) to conduct an intermediate self-examination to determine its metrological performance, coefficient error within the allowable range, or can not get accurate data.

Second, pay special attention to the measured liquid temperature. Many users ignore this point, that the temperature difference does not matter, our experiments show that: when the temperature deviation of 0.5 ℃, some liquid viscosity value deviation of more than 5%, the temperature deviation of a great impact on viscosity, temperature, viscosity decreased. So pay special attention to the measured liquid temperature is constant in the vicinity of the specified temperature, the best measurement is best not to exceed 0.1 ℃.

Third, the measurement of the container tube selection. For the double cylinder rotary viscometer to carefully read the instrument manual, different rotor cylinder matching the corresponding tube, otherwise the measurement results will be a huge deviation. For a single cylinder rotary viscometer, the principle of the outer radius of the outer tube is infinitely large, the actual measurement requirements of the outer cylinder that is measured the inner diameter of the container is not less than a certain size. For example, the Shanghai Tianping Instrument Factory produced NDJ-1 type rotary viscometer, requires the measurement of beakers or straight barrel with a diameter of not less than 70mm. Experiments show that, especially in the use of a rotor, if the container diameter is too small to cause a larger measurement error.

Fourth, the correct choice of the rotor or adjust the speed, so that the value between 20 to 90 cells.
The instrument uses a dial plus pointer readings, its stability and readings are combined together with 0.5 cells, if the reading is too small as 5 cells near the relative error caused by more than 10%, if you choose the right rotor or speed to make Reading in 50 cells, then the relative error can be reduced to 1%. If the indication is more than 90 cells, so that the hairspring produced by the torque is too large, easy to produce creep, damage hairspring, so be sure to correctly select the rotor and speed.

5, frequency correction. For the nominal frequency of domestic equipment at 50Hz, and China's current power supply frequency is 50Hz, we use the frequency meter to test the variability of less than 0.5%, so the general measurement does not require frequency correction. But for Japan and Europe and some of some instruments, the nominal frequency of 60Hz, must be frequency correction, otherwise it will produce 20% of the error, the correction formula is:
Actual viscosity = indicated viscosity × nominal frequency ÷ actual frequency

Six, the rotor immersed in the depth of the liquid and the impact of bubbles.
Rotational viscometer on the rotor immersed in the depth of the liquid has strict requirements, must be in accordance with the instructions required to operate some of the two-cylinder instrument on the test of the amount of liquid has strict requirements, must be measured with a cylinder. The rotor is immersed in the process of the liquid often with bubbles in the rotor after a period of time most of the floating will disappear, attached to the lower part of the rotor bubbles can not be eliminated, the existence of bubbles will give the measurement data to bring a large deviation, so tilt Slowly immersing the rotor is an effective way.

Seven, the rotor cleaning. The measuring rotor includes the outer cylinder to be clean and free of dirt. It is usually cleaned in time after the measurement, especially after measuring the paint and the adhesive. Pay attention to the cleaning method, you can use the appropriate organic solvent soak, do not use metal tools such as hard scraping, because the rotor surface with a serious scratch will bring the measurement results of the deviation.
(编辑:HengZheng)
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