Study On Intelligent Loadcell Digitizing Unit With High Precision

With the improvement of weighing technique, intelligent and digital facilities are requiredto replace the analog ones used before. According to the present situation and development ofweighing technique, methods related in intelligent, network and precision weighing arestudied in this thesis, and an intelligent loadcell digitizing unit separated from the analogloadcell is designed to realize the digital alteration that makes an analog loadcell change to anintelligent one. The contributions of the thesis are presented as follows:1) Based on mixed-signal Micro-Control Unit (MCU) C8051F350 which integrates a24-bit ? ? ? Analog to Digital Converter (ADC) inside, channel switching, ratio voltagemeasurements and six-wire technique are studied, and a loadcell digitizing unit is designedwith self-calibration and digital compensation. The unit can work precisely at differentenvironments within the absolute maximum ratings. Experiments show that the mentionedtechniques meet the requirement of precise weighing.2) An expanding work is conducted to make the conventional RS-485 interface circuit meetthe requirements of bus snooping, multi-talker detecting and competition, and thecoresponding communication protocol is established. As a result, this loadcell digitizing unitpossesses of the functions of digital transmitter and is ready for instructions in terms of ASCⅡcode. The unit adapts to both network environment and intelligent management.3) Some novel functions are promoted and implimented, including: steplessly adjustibleexciting source supply for loadcell; interface accommodating six-wire and four-wire loadcell;JTAG interface for in-circuit debugging, flash programming, and on-line firmware upgrade.These functions expand the design concepts of conventional loadcell digitizing unit.