The Development Of On-line Weighing System Based On Electromagnetic Force Equilibrium Transducer

The weighing and the ingredients'controlling are still carried out by manual on some pipelining production line, which not only wastes a large amount of human resources, but also is the bottleneck of high-speed production and quality management. To resolve this problem, the matched weight and measurement devices are urgent to need. The real-time on-line weighing system is designed to resolve the mass control in the high-speed production.First of all, based of the understanding and analysis of the research on dynamic weighing technology at home and abroad, the purpose and significance of this designed is derived and the focus and the difficult part of this design are listed.Secondly, the characteristics and the advantages and the disadvantages of the commonly used types of weighing sensors are compared, the advantages and characteristics of the electromagnetic force equilibrium transducer used in this design are analyzed, and the work principle of electromagnetic force equilibrium transducer is mainly introduced in the article. It works on the balance principle that the Ampere force of the power wire in the magnetic field is equal to the gravity force of the objects. The weight is proportional to the current when the magnetic field intensity B, the wire length L is constant values. The measurement method of electromagnetic force equilibrium transducer is active control, compared with the resistance gauge, using the electromagnetic force equilibrium transducer with the unmatched advantages can reach higher precision. The closed-loop control system and the open-cont??system are compared in the article by system block diagram and mathematical model. The electromagnetic force equilibrium transducer works in closed-loop control, which approach is not sensitive to the external disturbance and the changes of system parameters, can reach higher precision than works in open-loop control means.The overall structure of the system and hardware and software design is specifically introduced in the article. The whole system is divided into three parts, namely, transmission part, weighing part and output part. The product is transmitted to the weighing unit by the conveyor, weighing procedure is completed in the moments when the production passing by the weighing unit, in accordance with the default information to judge whether the product is qualified or not and the remove action control. The PID adjustable means is used in the sensor output data collection and control circuits to improve the system dynamic characteristic greatly, the speed of respond is high and steady error is small. In addition, the pulse width modulation A/D conversion mode is adopted, whose merit is high-precision. EPM570, MAX II series CPLD device of ALTERA, is used to replace the traditional series chips of 74XX in signal processing with more flexibility fore the hardware structure is completed by the software. ATmega16L, AVR chip of ATMEL, is used as main control chip. The EPM570's output data is read by external interrupt, judged by the weighing information to control the remove device and alarm circuits, the data's real-time transmission is achieved by the serial communication between the MCU and PC. The communication between the PC and MCU is through the RS-485 transmission means, which has more reliability compared by RS-232. In the software design, the programming thought of the whole program and the design of the flow chart are mainly introduced, the program to the??570, and the key issues in the PC software design are briefly introduced. PC receives and deals with the data from the serial port, draws the real-time broken line and histogram graph, computes the average value and standard deviation, etc. The data is stored in the background database for inquiries and statistics for the future.To be a system with high reliability, some measures in hardware and software about system reliability design and the attention matters of PCB layout are also introduced. The discriminate and processing to the data is very important to get a accurate and reliability weight information in motion. In addition to the analog filter means, the digital filter is used to filter the clutter signal, the piecewise linear interpolation is used to resolve the problem of nonlinear and the zero point tracking technology is used to resolve the zero drift. Some compensation measures are also needed in the design for the temperature, environment and other interfering factors will significantly affect the system to reach high precision, such as the temperature compensation circuits, the aging treatment to the magnet, mechanical parts, etc. At last, the system error is analyzed and the uncertainty is assessed through the experimental data analysis, a number of improvements and plans are proposed...