How to reduce the test error of rotational viscometer

Due to its simple structure, low price, convenient and practical advantages, the rotational viscometer is widely used to measure the dynamic viscosity of various fluids such as oils, paints, coatings, plastics, foods, drugs and adhesives.

However, according to the long-term inspection results, we found that the data deviation is very large when testing samples. There are many ways to reduce test error. Below we will summarize several methods to reduce the deviation from the test principle.

Performance indicators must meet the requirements of the National Metrology Verification Regulations. The instruments used should be checked periodically and, if necessary, an intermediate self-examination should be carried out to ensure that the measurement performance is qualified and that the coefficient error is withins the allowable range, otherwise accurate data cannot be obtained.

2. The temperature of the measured liquid.

Experimenters have proven that: when the temperature difference is 0.5°C, the difference in the viscosity value of certain liquids exceeds 5%, and the difference in temperature has a great influence on viscosity.

Therefore, special care should be taken 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 the measure.

3. Selection of the outer cylinder.

For the double cylinder rotary viscometer, please read the instructions carefully, different rotors correspond to different outer cylinders, otherwise the measurement results will deviate greatly.

For a single-cylinder rotational viscometer, in principle, the radius of the outer cylinder should be infinite, and theactual measurement requires that the inner diameter of the outer cylinder, that is, the measuring vessel, is not less than a certain size. Experience proves that especially when the No. 1 rotor is used, if the inner diameter of the container is too small, a large measurement error will be caused.

4. Correctly select the rotor or adjust the speed so that the indication value is between 20 and 90 divisions.

This type of instrument uses a dial plus a pointer to read, and its stability and reading deviation are combined to have 0.5 division. If the reading is too small, such as about 5 divisions, the relative error caused is greater than 10%, if you choose a suitable rotor or rotational speed to perform the reading in 50 divisions, then its relative error can be reduced to 1%.

If the indication value is greater than 90 grids, the torque generated by the hairspring will be too high, which will easily cause creep and damage the hairspring, so the rotor and gear should be selected correctly.

5. Frequency correction.

The rated 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 that the variability is less than 0 .5%, so the overall measurement does not need frequency correction.

But for some instruments in Japan, Europe and America, the rated frequency is 60Hz, frequency correction should be done, otherwise there will be 20% error, the correction formula is: actual viscosity = indicated viscosity × rated frequency ÷ actual frequency

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