机械设计汽车专业文献英文翻译外文于PLC高速IO口模拟信号的测量与控制论文.doc

┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装 ┊ ┊ ┊ ┊ ┊ 订 ┊ ┊ ┊ ┊ ┊ 线 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 湖北文理学院 毕业设计（论文）报告纸 - PAGE 1 - Measuring and Controlling of Analog signal Based on High-speed I/O port of PLC Frequency signal is gotten from voltage signal by external V/F converter, and then is sent to high-speed counter of PLC. As a host, CPU222 of Siemens S7-200 series PLC is used. Through programming PLC, input voltage is measured by high-speed I/O channels. High-speed digital pulse of variable duty cycle produced by PLC’s PWM pulse generator is turned into voltage signal of amplitude-adjustable after external RC low-pass filter circuit filter to achieve controlling of output analog. The method reduces the cost of measurement and control system via replacing expensive analog I/O modules. Peripheral circuit design and PLC program are given. Through analyzing and comparing data, it is found that the system can achieve ± 0.1% accuracy. I. INTRODUCTION PLC has advantages of high reliability, simple programming, easy learning, convenient usage and small volume. It can implement sequential logic control and automatic control of analog according to the requirement of technological process, so it is widely used in industrial field and also make a good control effect. In some systems controlled by PLC, the circumstance of measuring analog voltage signal often is encountered. Analog extended module of PLC is adopted to do some conversion work in this case. But these modules’ prices are close to the small and medium-sized PLC’s price, and only provide few input port. In addition, more one module is connected in order to practical application, whose expensive cost cause to decrease of performance cost ratio[1-8]. Based on CPU222 of Siemens S7-200 series PLC, use PLC’s high-speed digital I / O channel with low-cost add-in V/F converter to convert voltage signal into frequency signal and then send it into PLC’s