| Firstly, the principle of the microwave auto-measurement system is introduced in the paper. The system has changed the traditional manual measuring pattern with shortcomings of low speed, low precision, easily to be interrupted by people, and adopts the auto-measurement method that greatly improves measuring speed and precision. Besides, with this system, one port reflection coefficient, SWR can be got at dot-frequency. One port reflection parameters, two ports transmission parameters and Q value of microwave resonator can be measured over sweepfrequency. Adopting domestic popular graphic programming software——LabVIEW, the interface of this system is beauty and easily to be operated. This system is cost-effective, and it is used widely for microwave teaching and experiment.In the system, the data acquisition card as an important link which connects the microcomputer system and network analyzer, has played an important role. Nowadays, the application scope of the data acquisition system is becoming increasingly wider, and the types of the measuring signal and signal source mentioned are larger and larger, so the request for measuring is becoming higher. There are many data acquisition systems in our country, but many of them have defects such as few channels, low sampling rate, low speed of data transmission, low precision, hard to be operated, depending on a high request for the testing environment. The data acquisition system with wide application scope and high performance-to-price ratio is needed. Therefore, based on the research of data-acquiring technique, combined with the specification of the auto-measurement system, a set of technical program is proposed and a data acquisition card with many channels and high precision is designed. The card adopts the new technology which combines the MCU and CPLD, and has a high accuracy which is owed to 12-bit high sampling AD converter and 12-bit multi-channel DA converter being applied. Besides, it takes the serial port as the interface, which achieves the speedy and reliable data transmission between the MCU and the PC, and then display the data on the PC.This paper introduces the composing principle of data acquisition card particularly by hardware and software. The hardware is constituted by six modules: AD conversion module, DA conversion module, data output interface module, CPLD module, MCU module, serial port communication module. The MCU which provides data bus communicates with PC visa the serial port, and controls the CPLD to produce all conversion circuits and control signals other modules require. The high integration properties of CPLD could not only simplify the previous complicated circuitry designed by separating components and the hardware design, but also reduce the system's developing period and enhance the system's reliability and security. In addition, the ISP (In System Programmable) performance makes system's development more convenient. The software is made up of master computer and slave computer. The slave computer adopts the C language, based on the KEIL C which is popular in the current field of programming environment. The master computer adopts LabVIEW as the programming tool, communicates with MCU visa NI-VISA, and establishes a set of communication protocol.Finally, combining with the software of the microwave auto-measurement system, detection is carried through under the influence of point frequency and sweep frequency. It is shown from the final debugging results that the error measured by the data acquisition card that is designed by SCM and CPLD has met the technical requirements, which proves the feasibility and practicability of the scheme in this paper. Besides, it can also be widely used in many areas such as industry,instrument,mechatronics,intelligent furniture and so on.
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