How to Use Rotational Viscometer?

Rotational viscometer is widely used to measure the dynamic viscosity of various fluids such as grease, paint, coating, plastic, food, medicine, adhesive and so on. It is popular because of the simple structure, cheap price, convenience and practicality. But in the process of communicating with customers, it was found that many of them have some doubts about how to use the rotational viscometer correctly. Now ATO will tell you the correct use of rotational viscometer, so that you can use ATO’s rotational viscometer more efficiently and conveniently.

Measuring Principle of the Rotational Viscometer

Firstly, after starting the rotational viscometer, the zero position should be detected. This operation is generally performed without installing the rotor. And then the inner cylinder with radius R2 should be installed in the outer cylinder with radius R1, and the inner cylinder should be filled with viscous fluid. Next, the synchronous motor rotates at a stable speed and is connected with the scale disk. Then, the inner cylinder is driven to rotate by the hairspring and the shaft. At this time, the inner cylinder will be affected by the viscous moment of the fluid. The greater the effect, the greater the torque which is produced by the hairspring against the viscous moment, and the larger the scale indicated by the pointer. Finally, multiply the reading by a specific coefficient to get the dynamic viscosity of the liquid.

How to Use Rotational Viscometer Correctly?

According to the measuring principle of the rotational viscometer just explained, in order to obtain accurate and reliable measurement data, the following points must be noted when using:

1. The performance index of the rotational viscometer must meet the national testing requirements. And the rotational viscometer that has been put into use should be periodically verified, and if necessary (the instrument is used frequently or in a critical state of qualification), an intermediate self-check should be carried out to determine whether its measurement performance is qualified and whether the coefficient error is within the allowable range, otherwise rotational viscometer can not obtain accurate data.

2. Users should pay special attention to the temperature of the liquid being measured in the rotational viscometer which is easily ignored because they usually think slight temperature difference has no effect. But the experiment proves that: When the temperature deviation is 0.5 ℃, some liquid viscosity value deviation will exceed 5%. Therefore, the temperature deviation has a great influence on the viscosity. Once the temperature increases, the viscosity will decrease. Therefore, we should pay special attention to keeping the temperature of the tested liquid constant, and not to deviate from the specified temperature by more than 0.1℃.

3. Select the correct measuring container (outer cylinder). Before using the dual-cylinder rotational viscometer, please read the instruction carefully. Different rotors (inner cylinders) have corresponding outer cylinders. If they are not properly matched, the measurement results will deviate greatly. However, when using a single cylinder rotational viscometer , the radius of the outer cylinder is infinite, and the actual diameter of the outer cylinder should not be less than a specific size during actual measurement.

4. Correctly select the rotor or adjust the speed to ensure that the displayed value is between 20~90 divisions. Because the rotational viscometer reads through the dial and pointer, and the stability and reading deviation are 0.5 divisions. If the reading is too small, such as around 5 divisions, the error will be more than 10%; If the reading is above 90 divisions, the torque generated by the hairspring will be so large that the viscometer will easily generate pressure and then damage the hairspring. But the error can be reduced to 1% by selecting the right rotor or rotating speed so that the reading is in 50 divisions. So be sure to choose the right rotor and speed.

5. Pay attention to the depth of liquid immersion and the effect of bubbles. The rotational viscometer has strict requirements on the depth of liquid immersed in the rotor and must be operated in accordance with the instructions (some dual-cylinder rotational viscometers have strict requirements on the amount of liquid tested which must be measured with a measuring cylinder). Because there are often bubbles in the immersion process of the rotor, most of the bubbles will float up and disappear after the rotor rotates for a period of time, but the bubbles attached to the lower part of the rotor can not be eliminated sometimes, and the presence of bubbles will bring a large deviation to the measurement data, so dipping slowly into the rotor is an effective way to avoid.

6. Pay attention to clean the rotor. Make sure that there is no dirt before measuring the viscosity with a rotational viscometer and clean it immediately after measuring, especially after measuring the paint and adhesive. Also pay attention to the cleaning method: Soak it with a suitable organic solvent instead of scratching with a metal tool. Because serious scratches will lead to deviations in the measurement results.

7. Most of the instruments on the rotational viscometer need to be adjusted to keep horizontal. Pay attention to the level problem all the time during the measurement, otherwise the reading will be deviated or even unable to read.

8. Some instruments on the rotational viscometer need to be equipped with a protective frames. So please read the instructions carefully then start install.

9. Determine whether the sample to be tested in the rotational viscometer is Newtonian fluid. For non-Newtonian fluids, appropriate rotor, speed, and rotation time should be selected to avoid misunderstanding that the instrument is not accurate.

In summary, although the rotational viscometer is simple in structure and easy to use, if not used correctly, a qualified rotational viscometer will not be able to get accurate measurement results. 

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