The term "endurance" and the durability test were first introduced in OIML International Recommendation R76-1, "Non-automatic Weighing Instruments." The definition of the term and the test content indicate that it applies to weighing instruments with a capacity below 100 kg. Under normal operating conditions, the instrument must withstand 100,000 repeated loading and unloading cycles at approximately 50% of its maximum load. The durability error due to wear and tear must not exceed the absolute value of the instrument's maximum permissible error (MPE). Subsequent OIML international recommendations on weighing instruments have included durability testing requirements. However, aside from extensive research on durability testing for belt scales in my country, no other articles or reports on durability testing have been published. The content and results of a weighing instrument's durability test are closely linked not only to the instrument's subsequent calibration results but also to its reliability, service life, and standards. Here, I would like to share my understanding of durability for discussion and correction.
1. Durability of Non-Automatic Scales
According to the durability test for non-automatic scales, under normal operating conditions, loading and unloading must be repeated 100,000 times at 50% of the maximum load and still meet the requirement of not exceeding the maximum permissible error.
If a scale is used 100 times per day, 365 days a year, it will be used a total of 36,500 times per year. For 100,000 loading and unloading cycles, this equates to approximately 2.7 years. In reality, this durability test is very similar to a repeatability test of a scale, except that the durability test is performed much more frequently and only at a fixed load of 50% of the maximum.
The subsequent calibration period for scales is typically six months. The in-use error range is set at twice the maximum permissible error (MPE) at the time of initial calibration, i.e., 2MPE. Scales with a maximum capacity of no more than 100 kg are typically used in retail settings, and most operate at room temperature, not exceeding the scale's calibration temperature (-10°C to +40°C). Under normal circumstances, a scale that passes durability testing should not exceed its maximum permissible error (MPE) for at least two years. Based on this, can we assume that a scale will remain within its in-use error range within two years after initial testing, significantly extending the calibration cycle? On the other hand, to ensure that scales can withstand 100,000 loading and unloading cycles, it's reasonable to establish corresponding technical requirements in scale standards. 2. Durability of Truck Scales: As early as the 1970s and 1980s, to meet user demand, some scale manufacturers began increasing the maximum capacity and rated loads of truck scales. However, to most people's surprise, even under such loads, scales still suffered unexpected, irreversible structural damage. Despite this, manufacturers continued to set high capacities for their scales, while also instructing users to limit truck scale loads to highway load limits. At the time, there was no consensus worldwide on how to define truck scale capacities, and only the United States had undertaken some exploratory work, attempting to find a consistent method for defining truck scale capacities.

In 1986, informal discussions at the annual meeting of the National Conference on Weights and Measures (NCWM) in Albuquerque raised this issue, leading to the formation of an industry working group at an ad hoc meeting in 1987 to review the definition of maximum and range capacities. Subsequently, in 1987, the NCWM's Technical Specifications and Tolerances (S&T) Committee considered proposing a solution to this problem. At a 1988 interim meeting, the Scale Manufacturers Association (SWA) proposed the concept of rated concentrated load, which was endorsed by the S&T Committee. The SWA proposed linking the rated capacity of a truck scale to its rated concentrated load. The concentrated load capacity (CLC) value, specified by the manufacturer, is the maximum concentrated load the scale is designed to withstand. The relationship between this and the rated capacity of the truck scale is as follows: Maximum capacity ≤ CLC × (N - 0.5), where N is the number of sections on the scale. This notation eliminates misrepresentation of the scale's capacity and ensures that during segmented loading tests, the scale can still operate properly even when the maximum load reaches the CLC value. During use, the load does not exceed the CLC value, ensuring the safety and reliability of the truck scale. This was revised in the 1989 edition of U.S. Manual 44, adding the aforementioned requirements for the relationship between the maximum capacity, concentrated load, and the number of sections on the scale. It is important to emphasize that the technical requirements for dynamic truck scales must meet requirements in motion. These requirements must be based on dynamic testing and technical conclusions obtained under dynamic environmental conditions, not static stress calculations. For an industry like weighing, achieving satisfactory technical results under dynamic conditions presents significant challenges in practical operation, both in terms of technology, experience, manpower, and financial resources. However, since 1988, numerous weighing manufacturers and international weighing conferences have proposed various proposals and conducted tests regarding the need to add CLC technical requirements and how to determine CLC values, but no conclusions have been reached. It wasn't until the 1994 annual meeting that Metter-Toledo proposed using the Federal Highway Administration's Bridge Gross Weighting Formula B to determine the CTC rating. This formula is used to protect against damage to the bridge caused by excessive concentrated loads when vehicles pass through it. This formula most closely matches the safety protection requirements for dynamic truck scales. It simply considers the truck scale's sections or modules as equivalent to the bridge's interval load.

my country has conducted extensive research on the durability of belt scales, establishing a belt scale durability working group and investing significant manpower and financial resources. Although the results were presented at international weighing instrument conferences and received positive reviews, they were not fully recognized. Technical indicators for evaluating the durability of belt scales must be determined through on-site measurements of belt scales. Based on these results, durability tests specified in the calibration requirements can be used to verify whether laboratory tests can replace the durability assessment of belt scales in actual use. Therefore, over a period of time, technical requirements and test procedures for belt scale durability were developed. The CTC rating was determined using the Administration's Bridge Gross Weighting Formula B. This formula protects against damage to bridges caused by excessive concentrated loads when vehicles pass through them. This formula specifies the optimal load rating for truck scale safety protection. Simply consider the FHWA bridge formula by equating the truck scale segments or modules to the bridge interval load:
W = 500
L + N
N − 1
+12N + 36
Where, L is the distance between the first and last axles (feet) and N is the number of axle groups.
To relate the truck scale's CLC rating to the W value in the above formula, a correction, called "r," is added to the W value. This allows the CLC value to be calculated using a table lookup based on the L value and the number of axles on the truck scale. While this approach has its advantages, it is still relatively complex to implement in the field. This method was subsequently refined at the 1996 annual meeting.
The issue of preventing damage caused by vehicle dynamics due to "overloaded" driving has become a generally accepted technical requirement over the past 10 years since 1986. This article does not discuss or introduce the process and technical issues involved in setting CLC rating requirements. A more detailed introduction to the topic is provided in my translation of "Concentrated Load Capacity—An Overview," published in W&M magazine in April 1997, over 20 years ago. Since I have long since retired, readers should refer to the latest regulations for relevant regulations.

I believe that in addition to defining test objectives, methods, and requirements for the durability of scales as defined in international recommendations, regulations for scale durability could also include CLC ratings, similar to those for dynamic vehicles, to prevent damage caused by vehicle overloading and achieve results equivalent to those in durability tests. This is my perspective on dynamic vehicle durability requirements.

3. Durability of Belt Scales

my country has conducted extensive research on the durability of belt scales and established a belt scale durability working group, expending significant manpower and financial resources. The results were presented at international weighing instrument conferences and received positive reviews and recognition. The technical indicators for evaluating the durability of belt scales must be verified through actual on-site testing. Based on the results of these tests, the durability tests specified in the calibration requirements can be used to verify whether laboratory testing can replace the durability evaluation of belt scales in actual use. Therefore, over a long period of time, when developing technical requirements and test procedures for belt scale durability, testers should compare and analyze both indoor and on-site measurement data. Ultimately, a determination should be made as to whether indoor testing should fully or partially replace on-site belt scale testing. This is also the basis for establishing technical indicators and requirements for durability testing.
Fundamentally, I believe that for scales, durability primarily refers to the requirement for maintaining the scale's range measurement value within the error range, regardless of factors such as temperature. The force acting on the load cell under the belt scale's weighing assembly is typically expressed as follows:

Where q is the weight per unit length of the belt scale, 2L is the spacing between the weighing rollers, d is the alignment deviation, T is the belt tension, K is the belt effect coefficient, and n is the number of weighing rollers.

is the weight of the material on the load carrier. The weighing platform of a belt scale is essentially the same structure as the load carrier of a static scale. Therefore, its durability should be similar to that of a static scale after 100,000 loading and unloading cycles. Its durability is primarily dependent on the belt tension and the installation condition of the belt conveyor. Therefore, evaluating the durability of a belt scale is much more complex than evaluating the durability of a static scale after 100,000 loading and unloading cycles. It requires sufficient time to accumulate, analyze, and compare indoor and field measurement data to arrive at a reasonable evaluation standard. 4. Durability and Verification
China's weighing instrument verification procedures are essentially equivalent to the corresponding international recommendations of the OIML International Organization. These recommendations are directly translated into Chinese or slightly modified to form my country's verification procedures. This leaves many weighing instrument practitioners, including professionals, unaware or unclear about how to formulate weighing instrument verification procedures.

Developing weighing instrument verification procedures begins with determining the maximum allowable error for the instrument based on specific needs. Verification intervals are typically set at six months, allowing for a general assessment of the impact of hot and cold weather on measurement errors. Within this basic requirement, long-term measurements on a large number of products and instruments from different manufacturers, combined with statistical analysis of the data, are required to verify whether the predetermined maximum allowable error and verification interval for the instrument are reasonable and feasible. Otherwise, modifications should be made based on actual conditions, by a period of trial operation before finalization and formal approval. Therefore, developing a new calibration procedure or adding or removing a calibration item requires a relatively long period of time and careful testing to collect sufficient data. Calibration procedures are documents based on a large amount of scientifically reliable measurement data; conclusions cannot be easily drawn from simply conducting a research project or writing a paper.

Because the measurement errors of domestic crane scales could not reach the accuracy levels of European and American countries, we established different requirements for imported and domestic crane scales when developing calibration procedures for crane scales: imported crane scales were required to meet European and American standards, while domestic crane scales were calibrated according to our actual requirements.

Like calibration procedures, the development of durability tests should also be based on extensive measurement data.

However, calibrating large scales on-site or in the field, developing calibration procedures and conducting durability tests is a very arduous and long-term task. Durability testing of large scales, such as belt scales, requires physical measurements, making it an extremely challenging and demanding process. The intensity of a durability test should be much greater than that of a periodic verification during the use of a scale. For example, a 100,000-cycle loading and unloading durability test on a small scale is significantly more intense than a periodic verification.
I believe that the primary focus of a durability test on a scale should be on the variability of the scale's measurement range. When testing the repeatability and stability of the measurement range, the influence of influencing factors should be minimized. This primarily involves temperature, so that the effect of the temperature on the measurement range does not need to be considered during measurement. Instead, the focus should be on changes in the range repeatability under the same temperature conditions.