电气工程及其自动化外文资料翻译.doc

电气工程及其自动化外文资料翻译
毕业设计(论文)外文资料翻译系别: 电气工程系专业: 电气工程及其自动化班级: 电 031 姓名: 韩建英学号: 31 外文出处: Specialized English For Architectural Electric Engineering and Automation 附件:1、外文原文;2、外文资料翻译译文。指导教师评语: 签字: 年月日注:请将该封面与附件装订成册。 1、外文原文 Introductions to temperature control and PID controllers Process control system. Automatic process control is concerned with maintaining process variables temperatures pressures positions, and the like at some desired operation value. Processes are dynamic in nature. Changes are always occurring, and if actions are not taken, the important process variables-those related to safety, product quality, and production rates-will not achieve design conditions. In order to fix ideas, let us consider a heat exchanger in which a process stream is heated by condensing steam. The process is sketched in Fig. 1 Heat exchanger The purpose of this unit is to heat the process fluid from some inlet temperature, Ti t , up to a certain desired outlet temperature, T t . As mentioned, the heating medium is condensing steam. The energy gained by the process fluid is equal to the heat released by the steam, provided there are no heat losses to surroundings, iii that is, the heat exchanger and piping are well insulated. In this process there are many variables that can change, causing the outlet temperature to deviate from its desired value. [21 If this happens, some action must be