Attentions when measuring HPMC viscosity data

In order to obtain accurate and reliable HPMC viscosity data, you must pay attention to a few points:
First, the performance indicators of the instrument must meet the requirements of the national metrological inspection regulations.
The instrument in-service should be periodically verified. If necessary (the instrument is used frequently or in a critical qualified state), an intermediate self-check should be performed to determine that the metering performance is acceptable, and the coefficient error is within the allowable range. Otherwise, accurate data cannot be obtained.
Second, pay high attention to the temperature of the liquid to be tested.
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 °C, some liquid viscosity values deviate by more than 5%. The temperature deviation has a great influence on the viscosity, the temperature rises, and the viscosity decreases, or vice versa. Therefore, high attention should be paid to keeping the temperature of the liquid to be measured near the specified temperature point. It is best not to exceed 0.1 °C for accurate measurement.
Third, the selection of measuring container (outer cylinder)
For the double-tube rotary viscometer, read the instrument manual carefully, and the different rotors (inner cylinders) match the corresponding outer cylinders, otherwise the measurement results will be greatly deviated. For a single cylinder rotational viscometer, theoretically the outer cylinder radius is required to be infinite. In actual measurement, the outer cylinder, that is, the inner diameter of the measuring container is required to be not lower than a certain size. For example, the NDJ-1 rotary viscometer requires a measuring beaker or a straight cylindrical container with a diameter of not less than 70 mm. Experiments have shown that especially when using the No. 1 rotor, a large measurement error will be caused if the inner diameter of the container is too small.
Fourth, the correct selection of rotor or adjust the speed, so that the indication value is between 20~90 grids.
This type of instrument uses the dial and pointer to read. The stability and reading deviation are combined into 0.5 grids. If the reading is too small, for example near 5 grids, the relative error is more than 10%. If you select the right rotor or speed, to make the reading at 50 grids, then the relative error can be reduced to 1%. If the indication is above 90 grids, the torque generated by the balance spring is too large, it is easy to creep and damage the hairspring, so the rotor and speed must be correctly selected.


Post time: Mar-20-2019