1. Problem
In recent years, the product quality of domestic belt scale manufacturers has been significantly improved. In order to make their products have a recognized or legally recognized technical and metrological index, some manufacturers proposed to modify the original belt scale's highest level to 0.2, and also conducted extensive discussions on the connotation of belt scale durability and how to test it. Now I would like to talk about my views on the durability of belt scales for your reference.
2. About durability
The concept of durability of weighing instruments is learned from the text of the international recommendation OIML R76 (non-automatic weighing instruments). The relevant content in the 1992 edition is reproduced as follows: "Terminology: T.5.5.7 Durability error - the difference between the inherent error of the instrument during its entire service life and its initial inherent error. T.5.5.8 Significant durability error - a durability error greater than e.
Note 1: Durability errors may arise from mechanical wear or from drift and aging of electronic components. Significant durability errors only apply to electronic components.
2: For multi-division instruments, the value of e should correspond to its local measuring range.
The following situations are not considered to be significant durability errors, even if they exceed e; The error generated by the instrument after a period of use is obviously due to failure of devices and (or) components or due to interference, so that its indication:
- cannot be interpreted, stored or converted as a measurement result, or means that no measurement is possible, or is obviously wrong, so that it must be noticed by all persons concerned with the measurement result." Text: 3.9.4.3 The durability error caused by wear shall not be greater than the absolute value of the maximum permissible error.
— 1 — This requirement is based on the assumption that the instrument has passed the durability test specified in A6 of Annex A, which is limited to instruments with a Max ≤ 100 kg. "
"Annex A (Mandatory) A6 Durability test (applicable only to Class II, III and IV instruments with a Max ≤ 100 kg) The durability test shall be carried out after all other tests have been completed.
Under normal use conditions, the instrument shall be subjected to repeated loading and unloading of approximately 50% of the Max load. The loading and unloading shall be repeated for 100,000 times at a frequency that allows the instrument to reach equilibrium during loading and unloading. The loading force shall not exceed the force achieved under normal loading conditions. Before the durability test begins, a weighing test shall be carried out in accordance with the method described in A.4.4.1 to obtain the inherent error of the instrument. After the above loading is completed, a weighing test shall be carried out to determine the durability error caused by wear. If the instrument has an automatic zero setting or zero tracking device, it can be in operation during the test, and the zero error should be determined according to the method described in Article A.4.2.3.2. "
The following is the durability statement in the verification regulations of my country's belt scales.
"Term: T.7.5 Durability test is a test to check whether the tested belt scale (EUT) can maintain its performance characteristics after a period of use."
It should be pointed out that apart from this, there is no other wording about durability in the entire regulation.
The following are some statements about durability copied from the terminology (standard): "Significant durability error refers to a durability error greater than e. The following are not considered significant endurance errors for the purposes of this Recommendation, even if they exceed the values defined above; errors in an instrument after a period of use which are clearly due to damage to the device/component, or to interference or malfunction of the endurance protection feature, are indicated as follows: cannot be interpreted, memorized or transmitted as a measurement result; cannot be made to perform any measurement; or draws attention to a significant error in all such measurement results.
Finally, some terms and definitions related to endurance.
Endurance test:
A destructive or breakdown test, sometimes (in the case of an instrument) with increased inaccuracy due to wear. It is usually a test in which the same load is repeatedly applied at the point where the result is expected and the number of load life is calculated. An endurance test whose purpose is to test the number of times or time that an instrument or its components can be used. Breakdown test
An endurance test whose purpose is to test the mechanical strength of an instrument or its components or their ability to withstand permanent damage. According to OMLR60, the "durability requirements" for sensors are: "Durability (persistence, durability)
— 2 — The load cell be Suitably durable so that the reguirements of this Recommendation may be met in
accordance with the intended use of the load cell. (The sensor should be suitable for the recommendation and meet the requirements consistent with the intended use of the sensor).
In summary, the terms and definitions of durability of weighing instruments cited above. So far, OIML international recommendations have only proposed durability requirements for non-automatic weighing instruments, sensors and belt scales below 100kg. And only operational specific requirements are proposed for the test error of durability of non-automatic weighing instruments weighing less than 100kg, while only conceptual and inoperable "definitions" are proposed for the durability of sensors and belt scales. Only OIMLR76 international recommendations propose that durability tests are mandatory, which should be understood as being implemented by the legal department.
III. Characteristics of belt scales There are three types of weighing instruments that are closely related to their use conditions when they are actually used. The measurement results of dynamic truck scales and dynamic track scales are closely related to the "approach tracks (rails)" at both ends. Therefore, except for fixed dynamic truck scales, portable dynamic truck scales cannot be used for trade measurement abroad, but can only be used for monitoring. Because it is placed in different locations, the measurement results of the same vehicle may be significantly different. The third type of weighing instrument is the belt scale, whose weighing results are not only related to the installation conditions but also significantly affected by the state of the belt conveyor used. Almost all articles about belt scales mention the influence of the "belt effect" of the transmission belt when discussing measurement errors. The error caused by this effect is generally much greater than the influence of the "approach tracks" of dynamic truck scales and dynamic track scales. This is why the measurement results in actual use are often different from the promised indicators of the belt scale manufacturer and the results expected by the user. When designing a system for material transportation, considering the state of the transmission belt as an afterthought, the result is a transmission system that can be weighed incidentally and has unreliable accuracy. The real belt scale should be a transmission weighing system with a certain reliable accuracy and a transmission function.