Blog

The experience of some urgent problems in the use of truck scales in my country in recent years is very similar to the problems encountered in the United States in the 1980s. I published an article of my translation in the 7th issue of “Weighing Apparatus” magazine in 2009, and talked about the thinking and process of how the United States revised the truck scale standards and verification methods in response to existing problems. I originally wrote an opinion on this issue before the translation, but unfortunately I could not publish it.
my country is probably the country that produces and uses the most truck scales in the world. In the use of truck scales, due to inaccurate weighing, short service life of the scale, and poor stability, frequent inspections are required. In my opinion, the economic loss caused by this is greater than the loss caused by the previous problems of commercial scales. Therefore, the revision of truck scale standards and verification methods is a very important, urgent and serious issue.
It can be seen from the translation of “Weighing Apparatus” magazine that when the US revised the truck scale regulations, the zero point is to determine the maximum allowable concentrated load capacity (CLC-Concentrated load capacity) between a single span of the weighing platform. The basis is to borrow the formula B of the “Federal Highway Administration” approved by the government for the gross weight load of the bridge to find the maximum load of the truck scale on vehicles of different axle groups, and then refer to the factor called “r”. The concentrated load weighing capacity of the truck scale can be determined. This value is specified by the manufacturer and is also the concentrated load value of the weighing bridge designed by the manufacturer for a single span. Although the load value has nothing to do with the nominal weighing of the truck scale, in the U.S. Manual No. 44, a constraint condition between the two is stipulated, namely:
Nominal weighing capacity≤CLC×(N-0.5) where N=the number of sections of the truck scale.
The US 44 manual gives the bridge formula B and the table for finding the value of “r”. Here again, it is emphasized that the above “inequality” cannot be used to determine the causal relationship between the nominal weighing and CLC. In particular, the value of CLC cannot be “inferred” based on this relationship.
During verification, it is required that the CLC load is applied to the center of the span of the weighing platform segment, and it is still accurately weighed. And it is required that before one side of the weighing platform is loaded, the other side shall not exceed a quarter of the load value of the CLC type. The weighing instrument produced by the manufacturer shall be marked with the nominal weighing capacity and the centralized load weighing capacity. The nominal weighing capacity is defined as the total load that can be loaded evenly distributed on the weighing platform.
Combined with the situation of our country, due to the complex situation of our country’s vehicles, there are currently many models of different countries and many modified vehicles in China, which brings great difficulties to the regulation of the concentrated load value of the weighing instrument. In addition, in the past, my country used the average load method to verify truck scales. That is to say, according to the nominal weighing of the truck scale, which makes some manufacturers in pursuit of profit, the weighing platform components are made very thin. Although it can meet the one-time verification load, it can not withstand the multiple loads of the vehicle and it happens quickly. Structural damage. Some people in China hope to determine whether the weighing instrument is “qualified” by checking the rigidity of the weighing instrument. This method was adopted in my country in the 1970s and 1980s for track scales (mainly for deep foundation pit track scales). I personally think that this method is unreasonable and not easy to operate. Because the load-bearing device of a truck scale is a component, not a simple mechanical device, how to determine its “stiffness” is not easy to operate during inspection, and it is not reasonable to use simple calculations to determine its “stiffness”. More importantly, both truck scales and railway scales have so-called “light structure” load carriers in foreign countries. The deformation of this kind of weighing instrument can be very large when loaded, but the service life is still very long, and the weighing can be guaranteed to be accurate. Therefore, the regulation adopts “stiffness” to judge, which is not only difficult to operate, but also restricts the development of the carrier.
In the translation, attention should also be paid to the revision of the truck scale regulations. Since it was proposed at an international conference in 1986, the final revision was only approved by everyone in 1997. It is consistent with the provisions of the US Handbook No. 44. This is because the modification of a program standard involves not only the interests of the manufacturer, but also the interests of the user. To meet the new requirements, the manufacturer must change the existing production process and design, and also conduct tests to see what is new. Can your products meet the new regulations. In the process of revision of foreign regulations, all manufacturers participate, and there is also a process for users to understand the performance of new products. What kind of range and accuracy products are more reasonable and cost-effective to purchase. Most of the weighing instrument manufacturers in our country already have the ability to participate in manufacturing and revising regulations, and it is hoped that more experienced manufacturers will participate in the process of formulating or revising regulations and standards.
In the past, the verification of truck scales in our country was done in accordance with the international recommendation R76. I always believe that R76 is the basic specification for weighing instruments, and its focus is on small commercial weighing instruments. In the United States’ manual No. 44, we can see that there are two categories for class III scales, namely class III and class IIIL. Class IIIL is for large scales, such as truck scales, axle load scales, railroad scales, livestock scales, and large buckets. Scales and so on. It is also stipulated that the error value will increase by 1d for every 500d increments above 1000 divisions. It is not equivalent to Recommendation R76. Of course, these regulations must be consistent with the country’s regulations on the measurement errors of bulk commodities.
I think the following issues should be considered when revising my country’s truck scale standards and verification methods:
1. If my country adopts the “rolling load” method, it is first necessary to reasonably specify the concentrated load value of various range truck scales. It should also be pointed out that the “rolling load” test cannot replace the “eccentric load” test of the weighing instrument.
2. The truck scale should still be subjected to a uniform load test to determine the nominal load of the truck scale, that is, the maximum weighing capacity.
3. According to the criterion of nominal load≤CLC×(N-0.5), determine the rationality of the truck scale design.
4. Is it permissible to use more than three weighing sections? A load-bearing platform with 8 sensors and an overall load-bearing platform allow the use of at most several sensors.
5. For an outdoor truck scale, what should be the maximum number of divisions when there is no windshield?
These are some issues that manufacturers and users should pay attention to and correctly use truck scale weighing. Finally, generally in the revision of standards and verification procedures, there should be the support of the manufacturer, otherwise there will be free-to-air text revisions, and some major revisions should be supported by experimental data and economic analysis. There should also be statutory arrangements for how to deal with the original truck scale after the modification. After these years of development and progress in my country’s weighing instrument industry, we have enough experience and ability to modify the standards and verification methods of truck scales suitable for my country’s national conditions.