Research and Design of Measuring Accuracy Method of Electronic Belt Scale

0. The introduction

For the logistics of bulk bulk materials (coal, ore, etc.), most economical transportation methods take ships as the means of transportation, and belt conveyors are mostly used for loading, unloading and transportation [1-5].But the accurate measurement of bulk material is always a worldwide problem.In international and domestic trade, the measurement of bulk cargo in ships usually adopts the method of "water meter weight", which is used as the voucher for handling the handover, settlement, billing, customs clearance, tax calculation, claim for compensation and arbitration of import and export commodities.But the water gauge is affected by many external factors, so deviation control is always a difficult problem to solve.After years of scientific research and development, the electronic belt scale as a belt conveying bulk material metering device, has been more and more widely used, especially the emergence of high-precision array electronic belt scale, so that its application of recognition has been greatly improved.But because the electronic belt scale is the dynamic material on the belt in the metering operation, the deviation will inevitably appear in the dynamic metering process. How to find and correct the deviation in time is the key link to ensure the accuracy of the metering scale.In the process of the construction of fuel intelligence, according to the accumulation of decades of using electronic scale in this unit, combined with the actual situation of the site, the array type electronic belt balance was selected, and a real-time monitoring and tracking system of array type belt balance was designed.This system greatly improves the accuracy of measurement, can reflect the measurement deviation and deviation trend in real time and intuition.it can move forward the post-analysis of measurement deviation to the real time monitoring in the process.it provides a new idea for improving the accuracy of measurement of bulk materials.

1.Principle and error reason of belt scale

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

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

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

Three is the use error caused by environmental reasons, mainly including the influence of temperature and humidity, magnetic field, vibration.

Four is the use error of the electronic belt scale caused by the field installation and daily use and maintenance, mainly is the limited technical level of the installation personnel, the installation quality and debugging did not meet the use requirements, the installation position design is unreasonable, and the operation error occurs in the calibration process.

2.The method of improving the accuracy of belt balance

2.1 Selection of electronic belt scales

Electronic belt scales after years of development, has formed a number of series and models of products, how to choose the appropriate electronic belt scales to improve the accuracy of measurement is very important.Array type electronic belt scales developed in recent years have a great breakthrough in accuracy, mainly reflected in the theoretical research, such as the establishment of the latest theory of internal force and belt effect theory.Internal force theory of array belt scale.For a single weighing unit, the influence of the belt tension is the same as that of the traditional belt scale.In a continuously mounted weighing array, the belt tension effects of adjacent elements cancel each other out.In other words, the influence of belt tension inside a continuously installed weighing array becomes an "internal force", and its influence on weighing is zero. The influence of belt tension is limited to the units at the outlet and entrance of the array.Belt effect theory of array belt scale."Belt effect" refers to the hardness, weakness and other physical characteristics of the belt on the weighing effect.Under the action of belt tension, the groove belt is semi-rigid. When the height of the supporting point is not in a quasi plane, the belt will produce waves along the direction of operation, and its influence on weighing is called the "belt effect".The influence of "belt effect" changes with the hardness of the belt, the flow rate of the material, the flow rate of the environment, the temperature of the environment and other factors.By detecting and analyzing the sampling values of each unit, a mathematical model of the influence of "belt effect" is established and compensated.Based on the above theory, the accuracy of the array type electronic belt scale has been greatly improved on the basis of the highest accuracy of the original national standard, which can reach the standard requirements equivalent to 0.25 level.Therefore, from the aspect of selection, the array type electronic belt balance should be the first choice.

2.2 Array belt scale structure

Under the guidance of "internal force theory", the overall structure of the weighing unit is very unique. The single-point suspended weighing unit is shown in Figure 1.Using a special weighing sensor as a single point support, using a special scale structure, two or more groups of weighing roller installed to form an independent weighing unit, a group of (2 ~ 8 or more) weighing units by continuous installation, to form a weighing array.Belt scale adopts unique structure design of high bending performance, simple structure, light weight, quick and convenient site installation.The sensor has a number of excellent performance indicators such as resistance to horizontal force and partial load. Combined with the patented array structure, the overall performance is greatly improved, which plays a key role in improving the long-term stability of the belt scale.

2.3 Characteristics of array belt scale

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

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

② The single-point suspension weighing platform is a weighing sensor supporting more than two groups of weighing idlers. It has the advantages of ingenious structure, high weighing precision, good stability and free from daily maintenance.

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

2.3 Real-time comparison and tracking monitoring system of array belt scale

Deviation will inevitably occur in the dynamic metering process of the electronic belt scale. How to find and correct the deviation in time is the key link to ensure the accuracy of the metering scale.Have developed comparing two scale real-time monitoring and tracking system, the electronic scale metering error of later analysis comparing to process real-time monitoring, realize the barrier to prevent abnormal forward, make ordinary monitoring personnel on duty can discover the electronic belt scale occurred the phenomenon of deviation, so as to take measures to prevent and interrupt measurement deviation.The method and principle of double scale real-time comparison tracking monitoring system are as follows.Two array electronic belt scales of the same specification, the same parameters and the same manufacturer are installed in series in the same adjacent section.Each electronic belt scale is composed of eight groups of single point suspension weighing units.Two electronic belt scales, one for measuring scale, one for monitoring scale, before and after adjacent installation, measurement at the same time.In theory, two scales in the same time period of the measurement of the data are exactly the same.The real-time comparison tracking monitoring system collects the instantaneous and cumulative values of two electronic belt scales in real time, and establishes the comparison mathematical model by applying them.By calculating the accumulative value deviation and accumulative value deviation rate of the two scales, the allowable deviation range is set, and the real-time comparison tracking and monitoring system of the two scales is formed.When the deviation of the cumulative value of the double scale exceeds the set value, it will send out class C acousto-optic alarm;When the error rate of the cumulative value of the double balance exceeds the set error rate, it will send out the acousto-optic alarm of class B;When the deviation of the accumulative value and the deviation rate of the accumulative value of the double scale exceed the set value, the sound and light alarm of class A will be issued.All real-time comparison tracking monitoring systems are remotely connected to the working computers of the personnel on duty to monitor the operation of the electronic belt scales in real time. The personnel on duty shall handle the necessary measures according to the types of sound and light alarms, so as to realize the real-time control of the metering process.At the same time, the remote monitoring shows the real-time comparison situation of the double balance. Through charts and other forms, the real-time error value, error rate and error control range can be displayed concisely and compentively, and the real-time acoustic and optical alarm of out of tolerance can reflect the operation situation of the electronic belt balance in multiple ways.

3. Application of tracking system

When the instantaneous and cumulative values of the two electronic belt scales are collected in real time, the real-time comparison tracking monitoring system of the double balance carries out necessary processing on these data, transforms them into the form of intuitive charts and so on, and displays the real-time data list of the double balance, the historical data curve of the double balance, the deviation rate curve of the double balance and the error alarm chart of the double balance in real time.Through the recorded curve tracking system, it can easily track the whole operation of the electronic belt balance, and accurately locate the time point when the deviation value and deviation rate of the double balance of the electronic belt balance are maximum.At the same time, combined with the on-site all-around video monitoring system, the operation condition of the electronic belt balance and belt conveyor can be analyzed, and the accurate and reliable operation of the double scale of the electronic belt balance can be found to provide continuous improvement measures.

4. Track the effectiveness of the system

The real-time comparison tracking and monitoring system of double scales transforms the post-analysis of measurement error of electronic scales into real-time comparison and monitoring of the process, which realizes the forward movement of the threshold of abnormal prevention.At the same time, the remote monitoring displays the real-time comparison situation of the double scales, and displays the error value, error rate and error control range in a concise and concise way in the form of charts and other forms, and the real-time acoustic and optical alarm for overrunning, so as to ensure the alarm and reminder in the first time when the deviation occurs in the operation of the electronic belt scales.Because of the real-time comparison and tracking monitoring of the double scales of the electronic belt scale, the abnormal situation of the electronic scale can be found and alerted in time, and the abnormal treatment can be carried out in the first time, so that the accuracy of the coal measurement of the belt conveyor has been improved overall, and the accuracy and credibility of the measurement data of the electronic belt scale have been improved at the same time.The real-time comparison tracking and monitoring system of the array belt balance and double balance has been applied to the coal unloading wharf of a power plant and achieved remarkable results.According to the statistics of six consecutive months, a total of 66 50,000-ton seaborne ships, totaling 2.27 million tons, were discharged, reducing the error rate from 0.75% to 0.5%, and controlling most of them within 0.25%.

5 conclusion

The real-time comparison tracking and monitoring system of the array belt balance and double balance carries out necessary processing on the collected data of the two array electronic belt balance, transforms it into the form of intuitive charts and so on, and automatically generates the concise real-time data list of the double balance, the historical data curve of the double balance, the deviation rate curve of the double balance and the error alarm chart of the double balance.Through the curve tracking system, it can easily track the whole operation of the electronic belt balance, and accurately locate the time point when the deviation value and deviation rate of the double balance of the electronic belt balance are the largest.At the same time, combined with the on-site all-around video monitoring system, the operation condition of the electronic belt scale and the belt conveyor can be analyzed at that time, and the cause of the deviation value and deviation rate of the double scale of the electronic belt scale can be accurately found, so as to provide continuous improvement measures for the accurate and reliable operation of the electronic belt scale in the future.Therefore, the application of array electronic belt scale + real-time comparison tracking monitoring system has a very positive significance to improve the accuracy of electronic belt scale.

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