A truck scale is a rather special type of weighing instrument. Besides the fact that the objects it weighs are not only heavy but also have a large span, the weighing platform (load-bearing device) of a truck scale is often composed of multiple independent scale platforms. Moreover, in terms of its load, the distribution is extremely uneven. Even for the entire weighing platform, only a few load-bearing devices are carrying the weight of the vehicle wheel axles, to the extent that some of the scale platforms are empty. To save sensors, two adjacent scale platforms share a pair on adjacent sides
Sensors, these features do not exist in other weighing instruments. From the perspective of verification, since the weight of the vehicle being weighed is very large
It can be as large as 100t grade. If it is verified in accordance with the "requirements" of OIML R76 "International Recommendation for Non-Automatic Weighing Instruments", it will not only be time-consuming, laborious and costly, but also often fail to meet the verification requirements of the maximum range. In addition, due to the particularity of the objects being weighed by truck scales, evaluating the measurement and technical indicators of truck scales is also a matter that needs to be discussed.
In fact, we know very little about how foreign truck scales are inspected, and the OIML organization does not have any specific international recommendations for truck scales. Earlier, our verification of truck scales was generally carried out in accordance with the requirements of R76 "Non-Automatic Weighing Instruments". Later, by referring to the American "Manual No. 44", we learned that the technical standards for truck scales include requirements for the installation of weighing instruments: Concentrated Load Capacity (CLC), that is, the requirement for concentrated load values. Because we are not very familiar with the basis for the background of this technical indicator, it has not received the attention it deserves, and as a result, many professionals are unaware of such technical requirements. It was not until I read the article "Concentrated Load Capacity - An Overview" that I gained a more comprehensive and extensive understanding of CLC. In the United States, to avoid or
The issue of reducing the unexpected structural damage to truck scale Bridges was studied starting from 1998, and it took more than ten years until this technical requirement was included in the "Manual No. 44" from 1998 to 1999. The concentrated load capacity (CLC) should satisfy the following formula: nominal capacity<CLC× (N-0.5)
Here, N represents the number of weighing platforms included in the truck scale. A total of three metrological and technical requirements are defined for truck scales:
Nominal Capacity (standard load value) Sectional Capacity (segmented load value) Concentrated Capacity (concentrated load value)
Theoretically speaking, the greatest difficulty in calibrating or verifying truck scales lies in the fact that today's truck scales are basically composed of multiple independent weighing platforms, and two adjacent scales share a pair of sensors. It is required that these scales be independent when subjected to force and have no correlation with each other. This theory requires that the torque balance between adjacent weighing platforms be independent of each other and that the values of the torque balance be equal. Such a requirement requires that adjacent weighing platforms of the truck scale share a pair of sensors
In terms of the structure of the device, it is very difficult to adjust the torque balance requirements in practical applications. Because, for two adjacent scale platforms sharing a pair of sensors, it is almost impossible to simultaneously meet the condition that the two torque balances are independent of each other. During verification and adjustment, especially when there are no weights, the adjustment of truck scales is often actually to meet the "force balance" state rather than the requirement of torque balance of the weighing instrument. These two may lead to a significant difference between the final measurement results. Using "force balance" calibration actually means making the sensors used in truck scales output the same when the same force value is applied. But this so-called "force equilibrium" condition is wrong from a physics perspective
Wrong. According to the principle of static equilibrium in physics, only co-point force systems can achieve equilibrium of force values. The forces involved in truck scales are parallel forces. For such a parallel mechanical system, only moment balance exists. For torque balance systems with unequal force arms, the forces of each torque are not equal, that is, when weighing, the resultant force of the force values is not equal to the weight (quantity) of the object being weighed. This phenomenon is commonly seen when we debug or calibrate truck scales. If we calibrate the truck scale using the "force balance" method,
It often occurs that when the truck scale is at different positions on the load-bearing platform, the weighing result may exceed the maximum allowable error of the weighing instrument. Adjusting and calibrating truck scales based on the principle of torque balance is a method that does not violate physics and is the correct one. A calibrated and debugged weighing instrument will ensure that the weighing result does not exceed the maximum allowable error of the weighing instrument, regardless of the position of the vehicle being weighed on the weighing platform.
In fact, from a physics perspective, the correct method for calibrating and adjusting weighing instruments is to adjust or verify the principle of torque balance. The "force balance" calibration method is fundamentally incorrect, but in practical operation, it is also "feasible" based on actual requirements and conditions. It should be particularly pointed out here that the calibration method without weights is essentially a "force balance" calibration, and special attention should be paid when using it.