With the increase of logistics, people put forward higher requirements for the accuracy of weighbridge measurement. In the actual production process, there are many factors that affect the performance of weighbridge measurement. Therefore, it is of great significance to explain the working principle of the weighbridge, study the influencing factors and measures of the accuracy of the weighbridge measurement, and promote the measurement performance of the weighbridge and extend its service life.
introduction
With the continuous development of electronic information technology, the weighbridge has developed rapidly, especially in recent years, with the rapid development of transportation industry and the increase of modern logistics, and the weighbridge is not only convenient for weighing, but also fast, flexible and flexible, making great contributions to the development of China's economy. The modern weighbridge mainly uses three methods for weight measurement: vehicle, axle group and wheel weight. The advantages and disadvantages of the three weight measurement methods are obvious. The vehicle weight measurement method has high accuracy, but the disadvantages are large floor area, high price and poor mobility. While the axle group and camel weight measurement methods have the advantages of light weight, small floor area and ease of movement, they are not accurate enough. In particular, the wheel load electronic truck scale is easy to carry, and is widely used in highway overweight detection. However, due to the lack of accuracy and stability, its further promotion and application are limited. In recent years, the logistics volume has increased sharply, road transportation has increased sharply, the sensitivity of the wheel load weighbridge is limited, and weight measurement errors have occurred from time to time. Based on this, this paper puts forward effective measures to improve the measurement accuracy of the weighbridge on the basis of exploring the factors that affect the measurement accuracy of the electronic truck scale. It is of great significance to promote the measurement performance of the weighbridge and extend its service life.
1. Working principle of weighbridge
The essence of the weighbridge is a scale platform with electronic sensors. First, when the object passes through the truck scale, under the action of gravity, the load bearing sensor will deform after being compressed; Then, the Wheatstone bridge is unbalanced, and the output voltage signal is consistent with the object quality; Finally, after converter conversion, amplifier amplification and microprocessor processing, the digital signal consistent with the object quality is finally output
2. Factors influencing weighing accuracy and measures
2.1 Installation of Weighbridge
As a precision instrument, even if the product quality is qualified, the accuracy and stability of the weighbridge will be affected by factors such as installation, commissioning and construction personnel operation. The first is the site selection before installation. On the one hand, avoid the underground waterways, air ducts, etc., on the other hand, avoid electromagnetic interference. The installation location should avoid strong current and strong magnetic environment; At the same time, the location of the truck scale should be appropriate, and the observation positions at both ends of the distance from the surveyor should be moderate to facilitate the observation of the measurement results. The soil quality of the final site should be appropriate, not too dry, not too wet, and drainage should be good. The second is the construction link. On the one hand, the concrete shall be paved, and the center cross line shall be determined to determine the datum line of the weighing plane. The most important thing is to fix the foundation plate, so as to achieve seamless contact. The last part is the installation of the mechanical part. Before the installation of the scale body, it is necessary to check whether the installation of the foundation plate is reasonable according to the requirements. At the same time, it is necessary to check the position and size of the pit mouth and the composite sensor; Outdoor truck scale is easy to be struck by lightning. Therefore, lightning protection should be done well in the construction process. Once struck by lightning, the stability of the sensor will decline, or even the sensor will be damaged. Copper wire grounding can be used to form a loop with the earth, and the code will be struck by lightning. After installation, the automobile electronic scale shall be debugged as a whole according to the regulations. After calibration and debugging, the corresponding certificate shall be pasted according to the verification regulations, and then it can be put into normal use.
2.2 Vehicle performance
The static object has no impact on the scale body, so the weighing accuracy is high and the stability is good; The moving object, due to the existence of a certain speed and object vibration, will produce different pressures on the sensor. The force on the scale body is uneven and complex. The car connected by the leaf spring and the front and rear axle, in the process of running, due to the driving speed and body turbulence, makes the driving vibration distance. In the process of braking, makes the rear wheel friction great, the front wheel of the body will have a corner with the road, and the car will stop slowly after a period of time; If the car accelerates suddenly, under the effect of acceleration, the rear wheels of the car will turn due to inertia, and the wheels will also bump due to acceleration; At the same time, during the working process of the automobile engine, the automobile power system makes the automobile vibrate, which can be eliminated by different loads. When the load is relatively small, it only depends on the main spring buffer. When the load increases, the secondary spring also plays a good role in mitigating vibration, ensuring that the natural frequencies of the automobile under different loads are consistent, and avoiding damage to the structure due to strong vibration.
2.3 Straight approach road
The dynamic weighing of the weighbridge is helpful to improve the accuracy of the cross car only when the object passes the weighing scale smoothly. In order to make the car pass through the idler stably, the front and rear idler are generally leveled to ensure the stable passage of the car; When the dynamic truck scale is used for weighing, the way of paving the rail is generally used to make the car pass the heavy rail stably, so as to eliminate the vibration when the car passes. Generally speaking, straight roads with a horizontal approach of no more than 15m shall be used in front of and behind the weighbridge, and the straight roads shall be cleaned in time to ensure the smooth state of the straight roads. In addition, it should be noted that a car running on a smooth straight road can avoid braking and acceleration.
2.4 Metering speed
With the rapid increase of modern logistics, the ultimate goal of modern weighbridge is to achieve rapid measurement. However, the measured object needs to be transmitted through a series of measuring systems, and finally the test results will be displayed. The whole data transmission and conversion requires working time. Especially for fast moving objects, the measurement error is large. Therefore, it is necessary to continuously improve the working efficiency of the measurement system. At this stage, by extending the length of the weighing platform and adopting the method of multiple data acquisition, the working time of the measuring system is extended, so as to improve the measurement accuracy of the weighbridge. From this, it can be seen that the measurement accuracy can be effectively improved by extending the number of idlers and the time for objects to pass through the weighing platform. Practice has proved that the measurement accuracy can also be effectively improved by reducing the speed of objects passing through the weighing platform.
Weighing platform
As the core component of the weighbridge, the rationality of the strength, stiffness and limit of the weighing platform is of great significance to the accuracy of measurement. However, the length of the dynamic and static electronic truck scales varies greatly. The dynamic weighing platform is shorter than the static weighing platform, and the stiffness and strength are higher than the static truck scale, so as to ensure small deformation when the vehicle passes through and achieve the goal of rapid response. At the same time, the dynamic truck scale platform is applied to higher natural frequencies. For this reason, the dynamic truck scale usually adopts the method of welding steel plates as a whole and is connected with countersunk screws to ensure the smoothness of the scale platform. It should be noted that the approach road and the platform are combined in the form of trapezoidal teeth to alleviate the vibration when materials pass.
2.6 Sensor performance
The role of load sensor in the metering system is to collect data on the one hand, and provide a better supporting platform for the weighing platform on the other hand. However, due to the small area of the platform of the dynamic weighbridge, in order to ensure that the position of the load sensor is close to the edge of the platform, the platform must have enough span. In this way, once the load exceeds the edge of the weighing platform, it will cause the overturning of the other side. Therefore, it is pointed out that the stable moment when the material passes through should be greater than the overturning moment.
2.7 Limit
The limit is an important guarantee to ensure the accurate weighing of the dynamic weighbridge. However, the dynamic truck scale has a small scale surface, and the performance of buffering vibration is poor when the truck passes with full load. Some studies have pointed out that the pull rod limit method is used to make the vertical and horizontal limit in the same horizontal plane during installation, so as to avoid the sensor receiving additional external forces. When the vehicle passes, the scale platform is tightened, and the scale platform is tightened through the rod end spherical bearing to prevent the platform from vibrating.