Research Of HART Communication Protocol Used To Smart Transducer

Nowadays,fieldbus technique became very important in the world of process control,through which digital communication is used to fields instruments,this leads to a revolution to control systems.However,4～20mA analog signal instruments alse have a large application in industry,the HART communication protocol—a transitional protocol during transition from analog system to digital system—emerges as the times require.Based on Bell202 communication standards,HART protocol transfer data with different frequency signals and plus with analog signals of 4～20mA.It is characteristic that realizes digital communication in the transmission of analog signals,it has strong competition in this interim period and grows quickly because of this technology belongs to research of link between the preceding and the following.Firstly, in this paper, HART protocol is illustrated, it adopt a predigested mode of OSI/ISO in which have seven functional layers, only three layers have been used in HART protocol.Physical Layer specifies the transmittal manner of signal and voltage of signal, Data Link Layer specifies the device type and format of data transmit, Command Layer specifies all kinds of HART command and reoponse codes.Secondly, being based upon HART protocol,the method of smart transducer design is introduced, meanwhile make a feasibility analyse for HART retrofit of traditional transducer.through master the knowledge of HART protocol,this paper researches the system of smart transducer that it combines MCU with sensor.It importantly researches the hardware and software of smart transducer,the detailed hardware are introduced,including the single-chip microcomputer module,the sensor module,the communication module and A/D,D/A module.Then,the structures of software are analyzed and designed,the completion of Data Link Layer and Command Layer is emphasized,which including the realization of measuring and controlling program,communication program.Furthermore, data fusion is proposed to mitigate the crosstalks between different measured parameters.Finally, make the experiments and debugging through pressure smart transducer, at the same time, the problem and experiences I met in developing hardware and software of smart transducer system are summarized in the last of this paper.