Is a hanging scale an automatic weighing instrument or a non-automatic weighing instrument?

This question seems to be answered by Article 3.9.1.2 of the international recommendation R76, "Non-automatic Weighing Instruments" [1], which states "freely suspended weighing instruments, such as hanging scales or suspended weighing instruments".

Moreover, R76, "Non-automatic Weighing Instruments", states regarding the term "non-automatic weighing instrument": a weighing instrument in which operator intervention is required during the weighing process to determine whether the weighing result is acceptable. Two additional notes are added: Note 1: Determining whether the weighing result is acceptable includes human actions taken by the operator to affect the weighing result, such as actions taken when the reading is stable or when adjusting the weighing load, and deciding whether to accept the observed weighing result reading, or whether to print out the result. Non-automatic weighing processes allow the operator to take actions to affect the weighing result when it is unacceptable (i.e., adjusting the load, unit price, determining whether the load is acceptable, etc.). Note 2 points out that when it is unclear whether a weighing instrument is non-automatic or automatic, the definitions in the international recommendations for automatic weighing instruments OIMLR50, R51, R61, R106, R107, and R134 should be used instead of the standards in Note 1 for judgment. Since then, my country's crane scale product standards and related crane scale verification procedures have been based on the clauses related to non-automatic weighing instruments in the international recommendation R76. (1) A crane scale is a device that can weigh objects during the lifting process. It not only saves the time and manpower required for weighing, but also saves the space occupied by separate weighing operations. More importantly, in many continuous production processes where weighing is necessary but fixed weighing instruments cannot be used, crane scales are playing an increasingly important role in improving production efficiency, ensuring product quality, and guaranteeing safe production. The study of the accuracy of crane scales must fully consider the influence of the weighing environment. The effects of dynamic environment, wind force, and gravitational acceleration during weighing on the weighing results; the effects of sling tension on hook suspension or similar measurements; and the effects of cargo swing on weighing accuracy are all significant; especially the effects of cargo undergoing conical pendulum motion, which cannot be solved by any dynamic measurement method that simply uses mathematical processing. (2) The international recommendation for "Non-automatic Weighing Instruments" only introduces the test methods for conventional non-automatic weighing instruments in Appendix A, without introducing any test methods for crane scales. When the National Technical Committee on Metrology of Weighing Instruments revised the verification procedure for "Digital Indicating Scales" in 2016, it considered the special characteristics of crane scales. Therefore, when revising the verification procedure for "Digital Indicating Scales" [2], it specifically added test methods for crane scale performance. However, these are still test methods based on static conditions, which deviate from actual usage. (3) A few years ago, I heard that an expert wanted to compile a product standard for "Dynamic Crane Scales", but for some reason, it was not issued. In reality, simply classifying crane scales as non-automatic weighing instruments based on their application fails to address many practical issues.

Dynamic crane scales should refer to those that weigh while the load is being raised, lowered, and moved during the lifting process. Simply defining them as dynamic or static weighing makes differentiation difficult. "Dynamic weighing" implies relative motion between the load and the weighing instrument's support structure, whereas crane scales do not exhibit relative motion during weighing. However, in many crane scale applications, the lifting equipment itself...

Discussion on the Classification of Crane Scales

□ Shen Liren, Shandong Jinzhong Technology Group Co., Ltd.

[Abstract] The concept of a crane scale as a freely suspended, non-automatic weighing instrument is ingrained in most people's minds. However, in actual use, many crane scales are rarely stationary; they are always swinging or vibrating. How to define whether these crane scales belong to non-automatic or automatic weighing instruments is the question this article explores.

【Keywords】 Crane scale; Dynamic crane scale; Classification

Document Identification Code: B Article Number: 1003-1870 (2023) 02-0021-04

1. Because the object being weighed rarely reaches a stationary state in a short period of time, even if the reading is taken, it will deviate slightly from the reading when stationary.

1. Problem

The problem is that clause 3.9.1.2 of R76 International Recommendation is part of section 3.9.1, and section 3.9.1 introduces some regulations for "tilt" testing. It states that free-suspension weighing instruments such as crane scales are unlikely to tilt during use and do not require "tilt" testing, without introducing other requirements.

Crane scales include hook scales (see Figure 1), crane-type crane scales (see Figure 2), and gantry (bridge) crane scales (see Figure 3). Crane-type crane scales generally include trolley-type, wire rope drum-type, and pulley-type scales. Hook-type crane scales have the load cells directly mounted on the hook of the lifting equipment; this type of scale usually uses a combination of multiple load cells. Gantry (bridge) crane scales mostly use wire rope drum-type scales.

If we look at crane scales alone, we can define them as "non-automatic weighing instruments." However, if we consider the entire lifting system, whether it's a quay crane or gantry crane system in a port, or a bridge crane system in an industrial or mining enterprise, all rely on long wire rope connections, and the weight of the object being weighed is observed during lifting and movement. Due to this weighing method and the steel wire rope, two problems arise with the use of crane scales:

(1) During the lifting process, under the action of the lifting force of the equipment and the weight of the object, the steel wire rope suspending the crane scale will inevitably experience stretching and contraction. Sometimes, the lifting equipment suspending the crane scale will also vibrate. It is under this elastic action that the crane scale cannot promptly reach the indicated value of the weighed item.

(2) Generally, crane scales are used outdoors and are affected by the environment. Especially crane scales used at ports and docks are subject to wind, which causes the scale to sway, further promoting the vibration of the steel wire rope, and is also a factor affecting the timely acquisition of weighing results.
Looking at the current international recommendations on weighing instruments issued by the International Organization for Legal Metrology, I believe that there is a type of weighing instrument product in R51, "Automatic Catch Weighing Instruments" [3] that is more suitable for the use of crane scales. This type of weighing instrument is called "vehicle-mounted weighing instrument". Vehicle-mounted weighing instrument: This is a complete set of inspection scales designed for this specific purpose and installed on a vehicle. For crane scales, the crane (truck crane, overhead crane, gantry crane, bridge crane, gantry crane, etc.) can be called "vehicle", and the crane scale (hook scale, hook scale, etc.) can be called the weighing part. Automatic catch weighing instrument, where "catch" can be translated as: grab, hold; catch, capture, seize. The lifting of items by a crane scale can also be called "grabbing" or "holding". R51 can divide the weighing instrument into two basic categories according to its use: X or Y. Class X applies only to sorting scales used for inspecting pre-packaged products according to OIML R87 (Net Content of Packaged Goods), an international recommendation.

Class Y applies to all other automatic sorting scales, such as price-labeling scales, mail scales, and shipping scales, as well as many scales used to weigh loose, single loads.

Analyzing the types of scales described in this definition, while "price-labeling scales" and "mail scales" can be categorized as automatic scales, "shipping scales" are difficult to classify as "scales that automatically weigh according to a predetermined procedure without operator intervention." For example, vehicle-mounted scales (garbage scales) and vehicle combination scales (forklift scales, loader scales, etc.) do not meet this definition.

2.1 Non-Automatic (Static) Operation Performance Indicators
R51 has Class X and Class Y accuracy classes. The scale being inspected should be used according to the class that the inspection level can achieve. Because the maximum permissible error level for non-automatic operation of R51,

X III level and Y(a) level (Table 1) are basically on the same level as R76 III level (Table 2), both Table 1 and Table 2 are acceptable.