| Natural gas is a kind of important chemical raw material and clean energy sources. The volume measurement of Standard orifice is a major way in trade. Instead of the mechanical measurement, the DDZ instrument method is being widely used.Basing on the prospect of market and the state of natural gas measurement, the author develops FQJ-108 Natural gas measurement system. Its arithmetic standard is SY/T6143-1996, the idea of design is to use hardware platform of pc-base and software platform of embedded operation system.Measurement system is composed of computer, flow calculator and transmitter, configuration is very flexible. The computer is a HMI interface and Data Base Management platform. It provides various kinds of function, such as flow chart, real time dynamic display, real time and historical trend chart, alarm, report, data logging, parameter setting etc. The function of flow calculation and compensation, data acquisition and storage, communication is also provided in Flow calculator. The Field signal is converted into electronic signal by transmitter. Artic explains detailedly the principle and flow chart of hardware and software system .This papers gives simple iterative arithmetic of flow calculation. The precision of judgement and its value was changed, but the effect of iterative number and precision is roughly equivalent to fast Newton iterative arithmetic. Flow is added in the method of integration.The technology of micro-electronics and calculation method was fully made in the system. How to improve the accuracy of Standard orifice measurement is also discussed from the following aspects: the means of measurement and transmitter, online correction of measurement parameter and abnormal condition .All those means are used to overcome its shortcomings of less scale of measurement range, short period of checkout, more tache of maintenance and low accuracy of measure.The Modbus protocol is used as primary protocol in the system. When there is a user-defined communication protocol, it is converted into Modbus protocol through communication controller. Papers gives some solutions to improving efficiency and finishing project of remote communication. Software system can communicate with several hardwares at the same time. Flow calculator may be also accessed as single equipment in other systems.An Example is given in the papers to introduce function, graphics, flow calculation and compensation, report etc. The treatment of grounding and software is also suggested.In a word, we integrate into the system the advanced technology of computer,communication, control, sensor, measurement and database. The success of system consists in its structure, extensibility, development thought, online correction, real time online configuration, high-speed and multi-channels. In the end, it should be pointed out that Natural gas measurement system base-on field bus is an uptrend. The system prospects well.
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