The Research And Development Of Intelligent Pressure Transmitter Based On HART Protocols

Field bus, make relationships between the process control devices and even the high control management network, as a communication network among intelligent instruments in the field of process control automation, manufacturing automation. As HART field bus proposals a solution superimposing the digital signal at the present field control system without risk, the intelligent instruments based on HART field bus technique are widely used.With the development and appliance of the microcomputer and the embedded system, its high speed and agility are recognized by people. It is a trend to use microprocessor for a real-time supervisory control and data analysis. It has unexampled predominance in realizing the micromation, digital communication, intelligentize and network network connections of the instrumental production. The same time, it makes the instrumental production developmentting towards high accuracy, high reliability, high adaptability.In this paper ,the research and development of a intelligent pressure transmitter based on HART protocol is introduced , which is a project of guangdong xinhui instrument company.The intelligent pressure transmitter is built around a XE88LC05 microcontroller. The design of hardware and software as well as the implementation of HART digital communication are described concretely. The difficult problem in the design of intelligent transmitter, low power consumption technology is also presented.To overcome the output nonlinearity and temperature drift of pressure sensor, the method to reconstruct the sensor output with the input pressure and sensor temperature using bivariate polynomial is proposed. The coefficients of curved surface formulation are decided by the least square method and saved by EEPROM. Then the system can compute the input pressure depend on the curved surface formulation when the sensor output and temperature are knowable. The method it not only benefits temperature compensation but also helps non-linear rectifying.The advantage of the method proposed here is that it provides a way to get a consistent expression at the range of sensor calibration data, which eliminates the effect of output nonlinearity and temperature drift of the sensor and demands least data stored than the interpolation, and the accuracy of sensor can be reached to 0.2%.The intelligent pressure transmitter is universal for it can be used in many kind of sensor. Compare with overseas manufacture, it has more performance than cost.