The time of issue:2012-06-20 9:01:39 view number:
The viscosity tester is widely used in the determination of the dynamic viscosity of the grease, paints, coatings, plastics, food, drugs, adhesives and other fluids. The instrument is simple, cheap, convenient and practical, and therefore popular. The certification process has long been engaged in such instruments, we find that many users, especially SMEs testers in the course of many problems, often we test the performance of the instrument is better than the national metrological verification requirements, but users in the test sample when data bias. The correct use of such devices are accurate and reliable measurement results are analyzed as follows.
First, briefly explain the measurement principle of such devices:
To detect the grain viscosity tester boot after the first zero, this operation is generally not to install the rotor, and then install the coaxial outer cylinder of radius R1, the inner cylinder of radius R2, which is fraught viscous fluid, the synchronization motor rotates at a constant speed, a series of scale disc, and then driven by springs and the shaft within the cylinder (ie, rotor) rotating the inner cylinder (rotor) that is subject to the role of the viscous torque based on the fluid, the greater the role, the gossamer with them compete, the greater the torque, so the greater the scale indicated by the pointer on the dial. Reading multiplied by the specific coefficient of the liquid dynamic viscosity.
In order to obtain accurate and reliable measurement data according to its measurement principle, must note the following:
First, the performance of the instrument must meet the requirements of the national metrological verification regulations. Use instruments to carry out periodic testing, the instrument frequently used when necessary (or in a qualified critical state) to the middle of self-examination to determine its metrological performance qualified, the coefficient of error within the allowable range, otherwise it is impossible to obtain accurate data.
Second, pay special attention to the temperature of the fluid to be measured. Many users ignore this, that the temperature almost does not matter, our experiments show that: when the temperature deviation of 0.5 °„ C, some liquid viscosity deviation of more than 5%, the temperature deviation has a great influence on the viscosity, temperature, pressure, viscosity decreases . Therefore, pay special attention to the measured liquid temperature constant at the required temperature near the accurate measurement of preferably not more than 0.1 °ś.
Third, the choice of measuring container (outer tube). Binoculars automatic viscosity tester to read the instrument manual, the rotor (inner cylinder) to match the outer tube, otherwise the measurement results will be a huge deviation. For single cylinder rotational viscometer, the principle requires the radius of the outer tube is infinite, the actual measurement, the outer tube, inner diameter of the measuring container below a certain size. For example, Shanghai Balance Instrument Factory NDJ-1 rotary viscometer measuring beaker or straight describe a diameter of not less than 70mm. The experiment proved to be especially on the 1st rotor, if the container inner diameter too small to cause large measurement errors.
Fourth, the right to select the rotor or adjust the speed, so that shows the value of between 20 and 90 grid.
Of such devices by using the readings of the dial and pointer way, its stability and reading bias combination of 0.5 grid, if the reading is too small such as about 5 grid, causing the relative error of more than 10%, if you select the appropriate rotor or speed to make readings in the grid of 50, then the relative error can be reduced to 1%. If you show the value of more than 90 grid, so that the springs produce the torque is too large, prone to creep damage gossamer, they must be the correct choice of rotor and speed.
Five, the frequency correction. Domestic instrument nominal frequency of 50Hz, while China's current power supply frequency is 50 Hz, frequency meter test variability is less than 0.5%, it is generally the measurement does not require frequency correction. But for some Japanese and Western instruments, the nominal frequency at 60Hz, the need for frequency correction, or will cause a 20% error, the correction formula is:
Actual viscosity = Instructions viscosity°Ń Nominal frequency °¬The actual frequency
Six, rotor immersion depth of the liquid and bubbles.
Rotational viscometer rotor immersed in liquid depth, the stringent requirements must be in accordance with the specification requirements (some binoculars, there are strict requirements that must be taken with cylinder volume) instrument on the amount of test liquid. Often with air bubbles in the process of the rotor immersed in liquid, in the period of time after the rotor will go up the disappeared, attached to the rotor lower part of the bubble and sometimes can not eliminate the presence of air bubbles to the measurement data to a larger deviation, so the tilt slowly immersed in the rotor is an effective way.
Seven, the cleaning of the rotor. Measurement of the rotor (outer tube) to be clean and free of dirt, generally in the measurement and timely cleaning, especially in the measurement of paints and adhesives. Pay attention to the cleaning method of a suitable organic solvent soak, do not use metal cutting tools and hard scraping, because the surface of the rotor measuring the deviation of the results will bring serious scratches.
Eight, other problems needing attention.
A. Most of the instruments need to adjust the level of attention to the level of problems in the replacement of the rotor and adjust the rotor height and at any time during the measurement, otherwise it will cause reading deviations can not even reading.
B. Some instruments need to be installed to protect frame, carefully read the instructions required to install, otherwise it will cause reading deviations.
C. Determine the approximate Newtonian fluid, non-Newtonian fluid should be selected after the provisions of the rotor speed and rotation time, in order to avoid misunderstanding instruments are not allowed.
In summary, although the rotational viscometer structure is simple, easy to use, but if not used properly, a certified instrument can not get accurate results, affect product quality.