Design And Implementation Of Self-balancing Digitally Controlled DC Bridge

Because of the advantages of high measurement accuracy,good stability and low cost,bridge-method is still widely used in the field of precision resistance measurement.With the development and progress of technology,digital DC bridges began to replace traditional manual balancing bridges.At present,domestic digital DC bridge products have the disadvantage of poor stability,so there are few applications in the actual resistance precision measurement.Although the measurement accuracy of foreign digital DC bridge products is relatively high,but the price is extremely expensive,and it is not suitable for general resistance measurement occasions.Therefore,in order to make up for the shortcomings of domestic digital DC bridge products,it is of certain application value to study on a study on a digital DC bridge capable of automatic balance,high measurement accuracy and good stability.In this paper,an improved digitally control DC bridge structure is proposed by analyzing and comparing the principles of several balanced bridge structures.Around this structure,the design of the control circuit based on stm32f103c8t6 main control chip is completed,which can be divided into four modules:the main controller module,the human-computer interaction interface module,the improved bridge module and the voltage acquisition module.In addition,an independent stable power supply is designed for the embedded circuit.Using a fly-back-switching-power-supply scheme,an independent power supply is designed for analog devices and digital devices to avoid mutual interference between digital signals and analog signals.In order to realize the automatic balance of the improved numerical control DC bridge,the balance adjustment process of the DC bridge is analyzed.At the same time,in order to obtain better control accuracy,the continuous-domain-fuzzy-controller is selected as the balance controller.An improved bridge simulation model was established in MATLAB/Simulink,and the simulation verified the feasibility of the continuous-domain-fuzzy-controller.In addition,the detailed design process of implementing fuzzy controller using C language is introduced in detail.The software design adopts the embedded real-time system FreeRTOS as the core of programming,dividing different functions into independent task modules.The task modules are managed and scheduled by the system kernel to achieve the corresponding function,which improves the real-time response of the system and reduces the waste of control chip resources.At the same time,a human-computer interaction interface is designed,which can provide functions such as gear calibration,parameter reading and measurement result acquisition.This article elaborated the design process of software and hardware and its theoretical basis in detail.On this basis,a prototype measuring instrument for the new type of digital DC bridge was developed.After completing system commissioning,the performance of the circuit function module and the system function were tested.The test results showed that the indicators and performance meet the expected design requirements.