Research And Design of Measurement Accuracy Method of Electronic Belt Scale

0. Introduction

For the logistics of bulk bulk materials (coal, ore, etc.), most of the economic transportation methods are ship as the transport tools, and most of the loading and unloading transportation are belt conveyor [1-5]; The accurate measurement of bulk materials has always been a worldwide problem. In international and domestic trade, the measurement of bulk cargo by ship usually adopts the "water gauge weight" method, which is used as the evidence for handling the handover, settlement, billing, customs clearance, tax calculation, claim and arbitration of import and export goods. But there are many factors that influence the water gauge, so deviation control is always a difficult problem. After years of research and development, electronic belt scale as a bulk material metering device for belt transportation has been widely used, especially the appearance of high-precision array electronic belt scale, which greatly improves its application recognition. However, because the electronic belt scale is the dynamic material on the belt in the measurement operation, it is inevitable that there will be deviation in the dynamic measurement process. How to find and correct the deviation in time is the key to ensure the accuracy of the measurement of the scale. In the process of intelligent fuel construction, according to the accumulation of electronic scale used in our unit for decades, combined with the actual situation on the spot, the array type electronic belt scale is selected, and a real-time monitoring and tracking system of array belt scale is designed. The system greatly improves the accuracy of measurement, can reflect the trend of measurement deviation and deviation in real time and intuitively, and move the post analysis of measurement deviation forward to real-time monitoring in the process, which provides a new way to improve the measurement accuracy of bulk materials.

1. Principle of belt scale and the cause of error

The weighing bridge of electronic belt scale is installed on the conveyor frame. When the material passes the weighing bridge, the measuring roller detects that the material quality on the belt conveyor acts on the weighing sensor through the lever, and generates a voltage signal proportional to the belt load. At the same time, the speed signal of belt conveyor detected by speed sensor is also sent to weighing instrument. The instrument integrates the speed signal and weighing signal to obtain instantaneous flow and cumulative measurement. There are many reasons for the error of the belt scale, the main reasons are as follows.

One is the reason of the electronic belt scale itself. The main reasons for the error of the electronic belt scale system are temperature change, belt speed change, load change, vibration of the scale body and external interference.

The second is the use error caused by the belt conveyor, including the impact of the roller runout of the belt conveyor, the influence of the rigidity, thickness, shape and material of the belt, the installation quality of the belt and the influence of the tension device on the belt tension.

Third, the use error of belt scale caused by environmental reasons mainly includes the influence of temperature and humidity, the influence of magnetic field and vibration.

Fourth, the use error of electronic belt scale caused by the on-site installation and daily use and maintenance of belt scale is mainly due to the limited technical level of installation personnel, the installation quality and commissioning fail to meet the requirements of use, the installation position design is unreasonable, and the operation in the calibration process is wrong.

2. Methods to improve the accuracy of belt scale

2.1 Selection of electronic belt scale

After years of development, electronic belt scale has formed many series and models of products. How to choose the suitable electronic belt scale is very important to improve the accuracy of measurement. In recent years, the array electronic belt scale has made great breakthrough in accuracy, mainly reflected in theoretical research, such as the establishment of the latest theory of internal force and belt effect. The theory of internal force of array belt scale. For a single weighing unit, the belt tension has the same effect as the traditional belt scale; In a continuous mounted weighing array, the belt tension effects of adjacent units are offset. That is, the influence of belt tension in a continuous installation weighing array becomes a kind of "internal force", the influence of symmetrical weight is zero, and the influence of belt tension is limited to the unit at the entrance and exit of the array. The belt effect theory of the array belt scale“ Belt effect "refers to the effect of symmetry and heavy weight of physical properties such as hardness and weakness of belt. Under the action of belt tension, the groove belt is semi rigid. When the height of the support point is not in a straight plane, the belt will produce waves along the running direction and its symmetrical weight is called "belt effect"“ The influence of belt effect is changed with the change of belt hardness, material flow, environmental flow, and environment temperature. By detecting and analyzing the sampling values of each unit, the array belt scale establishes a mathematical model of the influence of belt effect and makes compensation correction. Based on the above theory, the accuracy of the array electronic belt scale has been greatly improved on the basis of the highest precision of the original national standard, which can meet the standard requirements of 0.25. Therefore, the array type electronic belt scale should be preferred in the selection of the products.

2.2 Structure of array belt scale

Under the guidance of the theory of internal force, the whole structure of the weighing unit is very unique. A special weighing sensor is used as single point support, and a special scale structure is adopted. Two or more weighing rollers are installed to form an independent weighing unit. A group (2-8 or more) weighing units are installed continuously to form a weighing array. The belt scale is designed with unique high bending resistance structure, which is simple in structure, light in mass, and convenient in field installation. The sensor has many excellent performance indexes such as horizontal resistance and partial load. Combined with the patented structure of array, the overall performance is greatly improved, which plays a key role in improving the long-term stability of belt scale.

2.3 Characteristics of array belt scale

The array belt scale has the following characteristics [6-10].

① The array belt scale is composed of several series arrangement of specific weighing units. The influence of belt tension can be eliminated by processing array data and the weighing accuracy of belt scale can be greatly improved.

② Single point suspension weighing platform is a weighing sensor supporting more than two groups of weighing rollers, with clever structure, high weighing accuracy, good stability, and no daily maintenance.

③ I-shaped single point weighing sensor is a special sensor for single point suspension weighing platform, which has the characteristics of unique structure, high weighing accuracy and strong anti horizontal interference ability.

2.3 real time comparison and tracking monitoring system of array belt scale

The deviation of electronic belt scale will inevitably appear in the dynamic measurement process. How to find and correct the deviation in time is the key to ensure the accuracy of measurement. In this paper, a real-time comparison and monitoring system of double scales is developed. The post analysis of the measurement error of the electronic scale is transformed into the process real-time comparison monitoring, and the gateway forward of abnormal prevention is realized. The ordinary on duty monitoring personnel can find out the deviation of the electronic belt scale in time, and take measures to prevent and interrupt the occurrence of measurement deviation. The method and principle of the double scale real-time comparison tracking and monitoring system are as follows. Two array type electronic belt scales of the same specification, same parameter and same manufacturer shall be installed in series in the same section adjacent to each other. Each electronic belt scale is composed of eight groups of single point suspension weighing units. Two electronic belt scales are one metering scale and one is monitoring scale, which is installed adjacent to the front and rear, and measured at the same time. Theoretically, the data measured by the two scales in the same period are identical. The real-time comparison and monitoring system of double scales collects the instantaneous value and cumulative value of two electronic belt scales in real time, and applies them to establish the mathematical model of comparison. By calculating the cumulative value deviation and the cumulative value deviation rate of the two scales, the allowable deviation range is set to form a real-time comparison and tracking monitoring system for the two scales. When the cumulative value deviation of double scale exceeds the set value, class C sound and light alarm will be sent out; When the cumulative deviation rate of double scale exceeds the set error rate, class B sound and light alarm will be sent out; When the cumulative value deviation and cumulative value deviation rate of double scale exceed the set value, a class a sound and light alarm will be sent out. All real-time comparison and monitoring system is connected to the duty personnel working computer remotely, and the operation of electronic belt scale is monitored in real time. The watchman shall carry out necessary treatment according to the sound and light alarm type, so as to realize the real-time control of the measurement process. Meanwhile, the remote monitoring and display the real-time comparison of double scales, through charts and other forms, it can display the error value, error rate and error control range in a concise and concise way, and give real-time sound and light alarm for the over error, and reflect the operation of the electronic belt scale in many ways.

3. Application of tracking system

When the instantaneous value and cumulative value of two electronic belt scales are collected in real time, the dual scale real-time comparison and tracking monitoring system shall process these data necessary, and form intuitive charts and other forms. The real-time data list of double scales, historical data curve of double scales, deviation rate curve of double scales and alarm chart of double scale error shall be displayed in real time. Through the recorded curve tracking system, it can easily track the whole process of the electronic belt scale, and accurately locate the time point of the double scale deviation value and the maximum deviation rate. At the same time, combined with the field full-scale monitoring system, the operating conditions of the electronic belt scale and belt conveyor can be analyzed, and the continuous improvement measures can be provided for accurate and reliable operation of the double scale.

4. Achievements of tracking system

The system of double scale real-time comparison and monitoring transforms the post analysis of measurement error of electronic scale into process real-time comparison monitoring, and realizes the gateway forward shift of abnormal prevention. Meanwhile, the remote monitoring and display the real-time comparison of double scales, and the error value, error rate and error control range are displayed concisely and concisely in the form of charts, and the real-time sound and light alarm of the difference is too poor to ensure that the electronic belt scale can alarm and remind the first time when deviation occurs in the operation. Because of the real-time comparison and tracking monitoring of the double scale of the electronic belt scale, it can detect and alarm the abnormal situation of the electronic scale in time, and can handle the abnormal situation in the first time, so that the accuracy of the coal measurement of the belt conveyor has been improved as a whole, and the accuracy and reliability of the measurement data of the electronic belt scale are improved. The real-time comparison and tracking monitoring system of array belt scale has achieved remarkable results after it was applied to the coal unloading terminal of a power plant. According to the statistics of six consecutive months, 66 50000 ton ships were unloaded, totaling 2.27 million tons, which reduced the error rate from 0.75% to 0.5%, and most of them were controlled within 0.25%.

5. Closing remarks

The real-time comparison and monitoring system of array belt weigher performs necessary processing to the data of the two array electronic belt scales, transforms into intuitive charts and other forms, automatically generates simple and concise real-time data list of double scales, historical data curve of double scales, deviation rate curve of double scales, alarm chart of double scale error, etc. Through the curve tracking system, it can easily track the whole process of the electronic belt scale, and accurately locate the time point of the double scale deviation value and the maximum deviation rate; At the same time, combined with the field full-scale monitoring system, the operating conditions of the electronic belt scale and belt conveyor can be analyzed, and the reasons for the deviation value and deviation rate of the double scale can be found accurately, and the continuous improvement measures for the accurate and reliable operation of the electronic belt scale in the future can be provided. Therefore, the application of array type electronic belt scale + real-time comparison tracking and monitoring system is of great significance to improve the accuracy of the electronic belt scale.

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