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The Results of a Rotary Viscometer Are Susceptible to These Seven Factors

June 30, 2020

Analytical Balance Manufacturer shares this article for you.

How to use rotary viscometer

1. Be sure to keep it level

2. When the rotor is placed in the sample, avoid generating bubbles, otherwise the measured viscosity value will be reduced. The method to avoid is to put the rotor into the sample at an angle, and then install the rotor. The rotor cannot touch the cup wall and the bottom of the cup. The sample to be measured must not exceed the specified scale.

3. When measuring different samples, the rotor must be kept clean and dry. If there are other samples or water remaining after cleaning, the accuracy of the measurement will be affected.

4. The acidic (PH)zui must not exceed 2, if the acidity is too large, a special rotor should be used, and the sample size must be determined when using ULA (only 16ml)

5. Select the viscosity standard liquid according to the measured viscosity range, and verify the instrument before using the rotary viscometer or rheometer every time, or periodically check to ensure the accuracy of the measurement. BROOKFIELD can provide silicone oil or oil standard products of various viscosity ranges that meet Newtonian fluid properties with an accuracy of ±1%. The recommended service life of the viscosity standard fluid is one year from opening.

6. When the value is relatively stable, otherwise the obtained value will have a large error

7. When selecting the rotor, it depends on the viscosity of the sample to be measured and the measurement range of the number of rotors is close, so choose the number.

8. When connecting the rotor, gently lift and pinch the mandrel (on the main unit) with the left hand, and rotate the rotor with the right hand. This operation is to protect the mandrel and hairspring in the fuselage, which can extend the service life of the instrument.

Digital Rotational Viscometer

Digital Rotational Viscometer

How to analyze the digital rotational viscometer accurately and reliably?

1. Periodic verification When necessary (the instrument is used frequently or in the critical state of qualification), intermediate self-examination should be conducted to confirm its measurement performance is qualified, and 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℃, 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, and do not exceed 0.1°C for the measurement.

3. Selection of measuring container (outer cylinder)

For the rotary viscometer, carefully read the instrument manual, different rotors (inner cylinder) match the corresponding outer cylinder, otherwise the measurement results will be huge deviation. In principle, the radius of the outer cylinder is infinite. In actual measurement, the inner diameter of the outer cylinder, that is, the measuring container, is not less than a certain size. Experiments prove 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, choose the rotor correctly 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, then the relative error can be reduced to 1%. If the indicated value is above 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 my country'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:

Viscosity = indicated viscosity × nominal frequency ÷ actual frequency

6, the depth of the rotor immersed in the liquid and the influence of bubbles

There are strict requirements on the depth of the rotor immersed in the liquid, which must be operated in accordance with 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 sometimes cannot be eliminated. The presence of bubbles will cause a large deviation 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.

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