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Research on Accuracy Evaluation Method of Gravity Automatic Batching Scale

Summary:

This article elaborates the research on various evaluation methods of the accuracy of batching and loading accuracy of gravity automatic batching weighing instrument, and draws a more scientific evaluation method.

Introduction

Gravity type automatic batching scales are widely used in feed, chemical, building materials and other industries as measuring equipment for production process. However, the national standard for gravity-type automatic batching scales is still under development. At present, the only batching scale standards for the feed and building materials industries are based on the corresponding static weighing scale standards, and the terms cited in the standards are OIML International. It is suggested that the relevant content of R76 "Non-Automatic Weighing Apparatus" seriously departs from the actual production and lags behind the technological development level of the batching scale industry.

1. Overview of Gravity Automatic Batching Scale

1.1 The concept and characteristics of gravity automatic weighing instrument

Gravity type automatic batching weighing instrument is a weighing instrument with one or more weighing units. According to the preset formula, the materials in the formula are weighed separately, and the total of each weighing is used as the general name of the automatic weighing instrument. Gravity-type automatic batching scales (referred to as "batch weighing scales") are commonly known as batching scales.

According to the number of weighing units, they can generally be divided into single weighing unit gravity automatic batching scales (commonly known as single-head batching scales) and multi-weighing unit gravity automatic batching scales (commonly known as multi-head batching scales).

Characteristics: ①The batching needs to be realized by multiple weighing processes; ②The formula used in the batching is artificially set in advance.

In some cases where manual weighing is used for batching, the requirements of OIML International Recommendation R76 "Non-Automatic Weighing Equipment" should be met, these are not the research objects of gravity automatic batching weighing equipment.

The loading of gravity type automatic batching scale is composed of multiple loads, and these loads are preset according to the requirements of the formula. These characteristics are just in line with the definition of OIML International Recommendation No. R61, "Automatic weighing instrument that divides bulk materials into many pre-defined, practically constant, separated loads from each other and loads them into containers".

Therefore, the gravity automatic weighing instrument meets the definition of a gravity automatic charging instrument and belongs to the category of a gravity automatic charging instrument.

Batching scales are mostly used for production process measurement, but in some cases, batching scales are also used for trade settlement.

1.2 Dosing scales and combined scales

The loading of batching scales and combination weighing scales are composed of multiple loads, but there are still big differences in technical characteristics between them:

① Although the loading is composed of multiple loads, during a production process, the number of loads and the weight of each load are fixed; and the combination of the number of loads and the weight of each load is based on the highest combination accuracy. The principle is determined by the calculation of the system computer. The weight value and number of loads for each load may change.

② Choose the combination scale to focus only on the weight of the load, but not on the weight of each load. While the batching scale pays attention to the loading weight, the weight of each load (proportion) is also an important index that must be paid attention to.

2. Possible evaluation methods for accuracy level

How to evaluate the accuracy of the batching scale more scientifically, more rigorously, and closer to the actual situation is a common problem faced by the batching scale industry.

There are three ways to evaluate the accuracy of the batching scale: the first is to only give the accuracy of the ingredients without considering the accuracy of the filling; the second is to only consider the accuracy of the ingredients without considering the accuracy of the ingredients; the last is to use Two indicators, batching accuracy and charging accuracy, evaluate the batching scale.

Considering that both the accuracy of the ingredients and the accuracy of the filling are required in actual production, the last evaluation method should be used.

2.1 Use the two concepts of ingredient accuracy and filling accuracy to evaluate ingredient scales

In the method of using the two concepts of ingredient accuracy and filling accuracy to evaluate the ingredient scale, the ingredient accuracy represents the accuracy of each component in the formula, and the filling accuracy represents the accuracy of the total weight of the formula.

In an actual batching scale, if the batching accuracy meets the requirements, the charging accuracy must meet the requirements, otherwise it is not.

For a more complete evaluation of the ingredient scale, the "rated minimum weighing" of the ingredient scale should be considered. The rated minimum weighing capacity is the minimum separation load that can meet the accuracy requirements of the ingredients. The component weight of the material in the formula should be greater than or equal to the rated minimum weighing capacity.

2.2 Evaluation method of ingredient accuracy

When discussing the accuracy of batching, for single-head scales, the accuracy level of each range segment corresponding to the weight of the material in the formula must first be tested using the R61 calibration method; for multi-head scales, the R61 calibration method must first be used to test The accuracy level of the range segment corresponding to the weight of the material in the formula of the weighing unit, and then processing these data, the following are possible processing methods.

2.2.1 Combination Evaluation Method

Considering that in the determined batching scale, each weighing process is independent, and there is basically no mutual constraint between the accuracy of each material. The batching accuracy level Xb of the batching scale can be expressed as a set of accuracy levels of each weighing unit. That is:

Xb = (X1, X2, ..., XN)

Among them: Xb is the accuracy of ingredients, X1, X2 ... XN is the accuracy of measurement of the corresponding range of the weighing unit corresponding to all materials in the formula.

For single weighing unit batching scales, N is the number of weighing sections corresponding to the components in the formula; for multi weighing unit batching scales, N is the number of weighing units corresponding to the components in the formula.

Advantage: It can give individual accuracy grade information of each component in the formula.

In production practice, the required accuracy of each material in the formula may be completely different, so this evaluation is closer to reality and more scientific.

Disadvantage: In this kind of disadvantage, the accuracy level is a set of accuracy, which is an array composed of the accuracy of each weighing unit, instead of a single accuracy level value that people are used to.

2.2.2 Weighted evaluation method

If the accuracy of each weighing unit obtained is (X1, X2, ..., XN), the accuracy of the batching of the automatic batching scale is expressed as Xb:

Xb => ： Research on Accuracy Evaluation Method of Gravity Automatic Batching Scale

Among them: pi is the weighting coefficient and should not be greater than 1> pi> 0.4.

Advantages: Using a weighted method can get a single accurate level of data, which is in line with people's habits.

Disadvantages: The weighting coefficient is difficult to determine or easily controversial; it is impossible to give personalized information on the accuracy of the formula in the batching scale.

For example, some "small ingredients" in production require very high accuracy of ingredients, while large amounts of main ingredients in the formula can reduce requirements.

2.2.3 Standard error method

If the accuracy of each weighing unit is (X1, X2, ..., XN), the batching accuracy of the automatic batching scale is expressed by Xb as follows: Study on the accuracy evaluation method of gravity automatic batching scale

Among them: Xb is the accuracy of ingredients, X1, X2 ... XN is the accuracy of measurement of the corresponding range of the weighing unit corresponding to all materials in the formula.

For single weighing unit batching scales, N is the number of weighing sections corresponding to the components in the formula; for multi weighing unit batching scales, N is the number of weighing units corresponding to the components in the formula.

Advantages: Using a weighted method can get a single accurate level of data, which is in line with people's habits.

Disadvantages: Can not give personalized information on the accuracy of the formula in the batching scale.

2.2.4 Maximum method

Use to find (X1, X2, ..., XN). Taking into account the international recommendation R61 to use the maximum processing method when measuring and setting deviations, the accuracy of the ingredients is expressed as:

Xb = MAX (X1, X2, ..., XN)

Advantages: Using a weighted method can get a single accurate level of data, which is in line with people's habits. In R61, this method is used to determine the setting deviation and measurement deviation, which is in line with the spirit of R61.

Disadvantages: Can not give personalized information on the accuracy of the formula in the batching scale. The conclusion is more extensive.

Combining the above methods, the combined evaluation method is more scientific and closer to the actual production, so it is recommended to adopt it in production.

2.3 Evaluation method of charging accuracy

2.3.1 Evaluation of total load accuracy

Treat the multiple loads in the formula as a complete charge, and use International Recommendation R61 to evaluate the accuracy of the charge. This is already fully expressed in International Recommendation R61.

2.3.2 Evaluating the accuracy of loading with the accuracy of each weighing unit

Similar to the accuracy of batching, the accuracy level of each weighing unit is processed according to the weighting method, standard tolerance method or maximum value method, and the processed result is used as the loading accuracy of the batching scale.

中 In the above two methods of evaluating the accuracy level of the charging. The second method is complicated in data processing, and there is no theoretical basis or actual precedent. The first method is in full compliance with the spirit of International Recommendation R61.

3. Concluding remarks

Scientific evaluation of the accuracy level of gravity automatic batching scales is a complicated system engineering, and there is no domestic or foreign experience to draw on. We have carried out a large number of practical tests and referenced previous engineering application cases and listened to the opinions of two experts, Shen Liren and Chen Rixing, in the research on the ingredients and loading accuracy evaluation method of the ingredient scale. In the case where the industry standard is still being formulated, it is a scientific and feasible method to evaluate the automatic batching weighing instrument with the accuracy of the ingredients in 2.2.1 and the accuracy of the charging in 2.3.1.

references:

[1] 《Automatic gravimetric filling instruments》 OIML R 61-1 Edition 2004 (E)

[2] "Gravity Type Automatic Loading Weighing Apparatus" Light Industry Standard of the People's Republic of China QB / T 2501-2000

[3] Verification Regulations for "Gravity Type Automatic Loading Weighing Apparatus (Quantitative Automatic Weighing Apparatus)"