Research On The Key Technology Of Intelligent Electromagnetic Flowmeter Based On HART Protocol

Electromagnetic flowmeter (EMF) rely on Faraday's law of induction. In electromagnetic flowmeter the flow rate is measured using the potential difference between tow electrodes when a magnetic field perpendicular to the flow is applied. Althought we had had a progress in empoldering EMF, we had lots of disadvantage in precision and anti-jamming. There are many reasons, such as loseing the excidion of little signal, having much conversion.Fieldbus Control System represents the direction of industry automation, which is growing more and more distributed and intelligent. To fund Fieldbus Industry Control System, it demands that all of the instruments in the system should have the function of Fieldbus Controlling. The HART protocol provides a uniquely backward compatible solution for smart instrument communication as both analog and digital communication signals are transmitted simultaneously on the same wiring. HART fieldbus technique is widely used in intelligent magnetic flowmeter. Aiming at the problems of our country's EMF and confirming the designing principle through analyzing the assignment of this item we puts forward the collectivity configuration of the intelligent EMF .The main work of the dissertation includes:In this paper, HART protocol is illustrated; its FSK Physical Layer specifies the transmittal manner signal and voltage of signal. Data Link Layer specifies the device type and data transport protocols. The Command Layer specifies the HART Command Set and Response codes. The Intelligent EMF, including both hardware and software, are realized on the foundation of these criterions.Introducing the design of the EMF hardware system, lays stress on analyzing the conversion and amplifying circuit, wave occurring circuit, the analog-digital conversion circuit, the keyboard display interface circuit, the communicating interface circuit and the anti-interference circuit.We adort a synchronization V/F conversion chip(AD652) to gather the voltage signal from transducer,so that we can get high precision.Adopting low-power CMOS chip P89C51RD2FN and X25045 to enhance anti-jamming,and predigesting circuit.In the communicating circuit, choosing HART signal proprieatary modem chip(HT2012)to realize the digital signal communication ,not disturbing 4～20mA simulate signals.Choosing MCS-51 assemble-langrage, we exertion modularization designing.Different modules have different functions, and any module has independency with others. With the particular analyzing of HART protocol, the method of software for implementing HART protocol communication in intelligent EMF is emphasized in the paper.Via Bell 202 modem, connecting PC's serial port with the resustance of intelligent EMF, so the intelligent EMF could communicate with Upper PC. The experiment shows that the intelligent EMF accords HART communicate criterion. Finally comparing the intelligent EMF with the standard EFM, the confirmation shows that the intelligent EMF can measure the voltage signal from transducer, realizing the functions of the intelligent EMF.