Problems related to test deviations of rotational viscometer

Rotational viscometer in the test sample occurred when the data deviation is large, how to correct this deviation, now on how accurate and reliable measurement results are analyzed as follows.

1. the rotary viscometer should be periodically calibrated
When necessary (the instrument is frequently used or in the qualified critical state) to carry out intermediate self-inspection to determine its metrological performance qualified, the coefficient error within the permissible range, otherwise accurate data can not be obtained.

2. pay special attention to the temperature of the liquid being measured
Many users ignore this point, that the temperature difference does not matter, our experiments prove that: when the temperature deviation of 0.5 ℃, some liquid viscosity value deviation of more than 5%, the temperature deviation on the viscosity of a great impact, the temperature increases, the viscosity decreases. Therefore, special attention should be paid to the measured liquid temperature constant in the vicinity of the specified temperature point, the measurement should not exceed 0.1 ℃.

3. the measurement container (outer cylinder) selection
For the double cylinder rotational viscometer should read the instrument manual carefully, different rotor (inner cylinder) match the corresponding outer cylinder, otherwise the measurement results will deviate greatly. For a single cylinder rotational viscometer, the principle requires an infinite radius of the outer cylinder, and the actual measurement requires that the inner diameter of the outer cylinder, i.e., the measurement vessel, is not lower than a certain size. The experiment proves that especially in the use of the first rotor, if the inner diameter of the container is too small to cause greater measurement error.

4. the correct choice of rotor or adjust the speed, so that the value between 20 to 90 cells
This kind of instrument uses the dial plus pointer way to read, its stability and reading deviation together with 0.5 frames, if the reading is small such as 5 frames near, caused by the relative error in more than 10%, if you choose the right rotor or speed so that the reading in 50 frames, then its relative error can be reduced to 1%. If the value is above 90 cells, so that the torque generated by the balance spring is too large, easy to produce creep, damage the balance spring, so be sure to choose the correct rotor and speed.

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

6. the rotor is immersed in the depth of the liquid and the impact of the bubble
Rotational viscometer on the depth of the rotor immersed in the liquid has strict requirements, must be operated in accordance with the instructions (some double cylinder instrument to test the amount of liquid has strict requirements, must be measured with a cylinder). In the process of rotor immersion in the liquid often with bubbles, in the rotor rotation after a period of time most of them will float up and disappear, attached to the lower rotor bubbles sometimes can not be eliminated, the presence of bubbles will bring a large deviation in the measurement data, so tilt slowly immersed in the rotor is an effective way.

7. the rotor cleaning
Measurement of the rotor (including the outer barrel) to be clean and dirt-free, generally in the measurement of timely cleaning, especially after measuring paint and adhesives. To pay attention to the cleaning method, available with suitable organic solvent soak, do not use metal knives and other hard scraping, because the rotor surface has serious scratches will bring the measurement results of deviation.