In order to ensure that the metering performance of the electronic balance meets the technical requirements, in short. First of all, to ensure the stability of the balance, and secondly to ensure the measurement requirements of the other three major performance. The balance of the four metrology performances complement each other. The mutual influence and mutual restraint are only guaranteed to ensure the accuracy and reliability of the balance weighing data.
Abstract: This paper analyzes and expounds the specific content, fault phenomenon, influencing factors and repair methods of the balance measurement performance.
Key words] stability sensitivity, correctness, invariance, fault correction
These four characteristics are interrelated and inseparable. Stability means that the analytical balance that has been balanced is disturbed by external forces. The measurement performance of the balance mainly includes stability, sensitivity, correctness and invariance of the balance indication. The ability to automatically return to the original equilibrium position after leaving the balance position. The better the stability, the more stable the balance. The stability of the balance depends on the position of the center of gravity of the balance beam. When the center of gravity of the beam is at a moderate position below the fulcrum, the balance is more stable (of course, the position of the center of gravity of the beam should be moderate below the fulcrum, not the lower the better, otherwise the sensitivity of the balance will be destroyed.) Conversely, the position of the center of gravity of the beam coincides with the fulcrum or Above the fulcrum, the more unstable the balance, the worse the stability. Since the stability of the balance is closely related to sensitivity and indication invariance, the measurement of the balance only requires verification of the three metrological properties of sensitivity, correctness and invariance. The sensitivity, correctness and invariance of the balance are three rare measurement phenomena and the causes and adjustment methods are
First, sensitivity
It also refers to the ability of the balance to detect the amount of change in the mass of the object placed on the weighing pan. It is usually expressed in terms of sensitivity, which is the property of a balance that reflects small changes in weight or mass. Sensitivity is the specific magnitude of the sensitivity of the balance. After the balance is balanced, the distance the pointer moves on the label is called sensitivity when each 1 milligram weight is added. The sensitivity of the left and right discs of the balance at no load and full load refers to the ratio of the line displacement or angular displacement of the tip of the balance pointer to the displacement mass. The sensitivity of the balance is independent of the mass of the substance referred to in the two plates. The balance indexing sensitivity is the number of divisions of the balance sign caused by the unit mass. The greater the distance the balance pointer moves (that is, the more the offset number is offset), the higher the sensitivity, the more sensitive the balance. The index value is the quality value that causes the unit index, so the smaller the mass value, the better the sensitivity of the balance.
The sensitivity of the balance does not reach the technical indicators, the influencing factors and the repair method are
Prevent water vapor and corrosive gases from entering the room. 1 Center of gravity is too high or too low. It can be solved by adjusting the position of the center of gravity ball by lowering or raising it. 2 Knife, knife bearing is broken or severely worn. The knife and knife can be replaced. 3 The ambient humidity is too large. The balance chamber should be dry, bright, and the temperature is not shaken. The window zui is open to the north. In order to prevent the unevenness of the balance between the two arms, the heat source should be separated by appropriate methods around the balance. It should be kept at an appropriate distance from the heat source such as heating, electric stove, oven, lighting, etc., and the exhaust fan, air conditioner and other electrical equipment with large power to prevent it. The single arm of the balance is affected by cold and hot air. 4 technical problems of each component device. The correct installation and use of the balance is directly related to the measurement performance of the balance and the service life. The measurement performance is reduced, the weighing error will occur, and the measurement will be affected.
The balance should be placed on a cement platform that is stable, strong, and off the wall. therefore. If the surrounding environment is vibrating and cannot be eliminated, the safety should be placed on the table with anti-vibration protection function to reduce the balance and protect the blade. 5 null, full load sensitivity is inconsistent Fault: 1 offline: full load sensitivity is lower than no load. The three-blade can be removed by raising the edge cutter. 2 eating line: full load sensitivity is higher than no load. The three-blade can be removed by flattening the edge cutter. The sensitivity of the left and right discs is inconsistent. Fault: The friction between the two sides of the blade and the cutter bearing is inconsistent. The position of the middle knife and the knife holder can be adjusted. If the wear is serious, the middle knife should be replaced. 2 If the length, hardness and sharpness of the two sides of the knife are inconsistent, the two sides of the knife should also be replaced.
Second, invariance
Its reproducibility of the balance position. It also means that under the same conditions, the balance is invariant and the balance is turned on multiple times without changing the existing state of the balance. The same object is continuously weighed multiple times to measure the consistency or reliability of the weighing result obtained each time. Invariance of indication value for multiple measurements of the same object, the smaller the variability of the measured value, the better the invariance of the indication of the balance, and vice versa, the worse the invariance of the indication of the balance. The magnitude of the indication invariance is related to the position of the center of gravity of the balance, and also related to various factors such as the adjustment of the beam itself, especially the three-knife adjustment state, operation, temperature difference, airflow, vibration, and static electricity. Generally, the variability of the balance is required to be as small as possible.
The invariance of the indication value is not affected by the technical indicators and the adjustment method is
The expansion coefficient of the beam data at each point is inconsistent. It can be solved by replacing the knife, the knife holder and the beam. 2 technical problems of assembly. When the device is installed, the three blades are not parallel, and the texture of one knife and knife is not good. The accuracy of the knife bearing is not enough, the braking position is not accurate, the eating is too large, the force of the beam is uneven, and the screw fastening level is inconsistent. The solution can be eliminated by re-correcting the device. 3 no-load variability. Mainly caused by mechanical transmission failure, eliminating the local failure of mechanical transmission. 4 full load variability. Mainly because the three blades are not horizontal and non-parallel, the parallelism of the three blades can be adjusted so that the blade is perpendicular to the centerline of the beam and in a plane. 5 The impact of the working environment, vibration, heat source, airflow, excessive humidity, static electricity, etc. in the indoor environment of the balance can be solved by improving the environment of the balance chamber. 6 The operator's operation method is improper. It can be ensured by strengthening training, improving the operation level of the post operators, and strictly abide by the management methods such as operating procedures.
Third, correctness
It is used to indicate whether the difference between the lengths of the two arms of the balance beam has the correct fixed proportional relationship. The correctness is usually called the unequal arm or deviation of the balance. The difference between the lengths of the two arms of the beam (deviation) should meet certain requirements. The correct proportional relationship is 1:1. If the two arms are not equal, the measurement result will be misaligned, and as the load increases, the unequal arm error will also follow. Increased. For single-disc balances, because the beam design requirements are in the form of unequal arms, there is no unequal arm error.
The same weight is placed in the two weighing pans of the equal arm balance for the equal arm balance. In theory, the moments on both sides of the balance should be equal and balanced. In fact, the lengths of the arms of the equal-arm balance are not absolutely equal. Although the weights of the two plates are exactly the same, the balance pointer will not completely return to the equilibrium position at the time of no-load, and will always deviate from the original equilibrium position. The difference, the magnitude of the deviation increases as the load increases.
There are many reasons for the unequal arm (deviation). 1 technical level of assembly. 2 The two-arm production data of the two beams is not equal, the manufacturing data density is not uniform, the length of the left and right arms of the beam is different, or the beam is deformed after loading.
The indoor temperature is not uniform and the factors are affected. 3 ambient temperature effects. The balance is heated or cooled by a single arm or part.
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