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1. the performance index of the instrument must meet the requirements of metrological verification regulation.

the instruments in use shall be subject to periodic verification. if necessary (the instruments are used frequently or in a qualified critical state), intermediate self-examination shall be carried out to determine that their metrological 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 doesn't matter at all. our experiments have proved that when the temperature deviation is 0.5 ℃, the viscosity value deviation of some liquids exceeds 5%, and the temperature deviation has a great impact on the viscosity. when the temperature rises, the viscosity decreases. therefore, pay special attention to keep the temperature of the measured liquid constant near the specified temperature point, and do not exceed 0.1 ℃ for accurate measurement.

3. selection of measuring container (outer cylinder).

for the viscometer, carefully read the instrument manual, and different rotors (inner cylinder) match the corresponding outer cylinder, otherwise the measurement result will have a huge deviation.

4. select the rotor correctly or adjust the speed so that the indicated value is between 20-90 grids.

this kind of instrument adopts the dial plus pointer method to read, and its stability and reading deviation are combined to have 0.5 grid. if the reading is too small, such as around 5 grid, the relative error caused is more than 10%. if the appropriate rotor or speed is selected to make the reading at 50 grid, the relative error can be reduced to 1%. if the indicated value is above 90 grids, the torque generated by the hairspring is too large, which is easy to creep and damage the hairspring. therefore, the rotor and speed must be correctly selected.

5. frequency correction.

the nominal frequency of domestic instruments is 50hz, and the current power supply frequency in china is also 50hz. we use a frequency meter to test the variability of less than 0.5%, so the general measurement does not need frequency correction. however, for some instruments in japan, europe and the united states, the nominal frequency is 60hz, so the frequency must be corrected, otherwise 20% error will occur. the correction formula is: actual viscosity = indicated viscosity × nominal frequency ÷ actual frequency.

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

the rotary viscometer has strict requirements on the depth of the rotor immersed in the liquid, and must be made according to the requirements * of the manual. there are often bubbles in the process of rotor immersion in liquid, and most of them will float up and disappear after the rotor rotates for a period of time. sometimes the bubbles attached to the lower part of the rotor cannot be eliminated, and the existence of bubbles will bring great deviation to the measurement data, so dipping the rotor slowly and obliquely is an effective method.

7. rotor cleaning.

the rotor (including the outer cylinder) used for measurement should be clean and free of dirt. generally, it should be cleaned in time after measurement, especially after measuring paint and adhesive. pay attention to the cleaning method. soak it in a suitable organic solvent. never scrape it hard with a metal knife, because serious scratches on the rotor surface will lead to the deviation of the measurement results.