Dynamic Weighing System Based On Cortex-M3

Electronic belt scale is a metrology instrument， which can continuouslyweighs the material on the belt conveyor. Electronic belt scale is widely used inindustrial production and trade flows. With the development of the sensortechnology and computer technology, the weighing technology has made greatprogress in digitization，intellectualization and informatization.Current kinds of belt scale can not meet the needs of various signal types. Inorder to solve this problem, a dynamic weighing system is designed in this thesisbased on Cortex-M3. The system integrates the functions of the measuring scalesand batching scales, and meets the demand of multi-signal type in the market.In the thesis, the structure and principle of the belt scale and load cell areanalyzed in detail, and the structures of hardware and software are given. Theweighing system integrates the measurement of multi-variable signals, dataprocessing, display, and transmission.The hardware of system consists of signal acquisition and processing module,signal-output module, and data transmission module, etc. Signal acquisition andprocessing module completes the shaping and counting of the pulse signal. Andthen，the analog signal is converted into digital signal by ADC (Analog-to-DigitalConverter) in the module. The signal output module performs the function of theanalog output of flow and load, and the pulse signal output of tons. Based on thedifference of the flow and set value from exterior, which is processed by the PID(Proportional-Integral-Differential) control algorithm, the module exports4-20mADCcurrent to control frequency converter, in order to mix the ingredients at precise rate. Thedata storage and display module completes saving and display of data processed,and provides functions of data querying and modifying. The module of datatransmission synchronizes the data between the host and slave based on485Bus. Thebasic structure and principle of each module, the circuit design, and the solution tothe problem of debugging are discussed in detail. The system software is designedaccording to the principle of the belt scale, and completes the functions of eachmodule with the hardware. At last, the test results show that the maximum errors ofthe load accumulated and stability of zero are0.09%and0.004%, which are betterthan the national standards.