PID中英文.doc

附录一 英文原文 外文出处： Specialized English For Architectural Electric Engineering and Automation Introductions to PID controllers PID controllers can be stand-alone controllers (also called single loop controllers),controllers in PLCs, embedded controllers, or software in Visual Basic or C# computer programs. PID controllers are process controllers with the following characteristics: _ Continuous process control _ Analog input (also known as “measurement” or “Process Variable” or “PV”) _ Analog output (referred to simply as “output”) _ Setpoint (SP) _ Proportional (P) , Integral (I) , and/or Derivative (D) constants Examples of “continuous process control” are temperature, pressure, flow, and level control.For example, controlling the heating of a tank. For simple control, you have two temperature limit sensors (one low and one high) and then switch the heater on when the low temperature limit sensor turns on and then turn the heater off when the temperature rises to the high temperature limit sensor. This is similar to most home air conditioning heating thermostats. In contrast, the PID controller would receive input as the actual temperature and control a valve that regulates the flow of gas to the heater. The PID controller automatically finds the correct (constant) flow of gas to the heater that keeps the temperature steady at the setpoint.Instead of the temperature bouncing back and forth between two points, the temperature is held steady. If the setpoint is lowered, then the PID controller automatically reduces the amount of gas flowing to the heater. If the setpoint is raised, then the PID controller automatically increases the amount of gas flowing to the heater. Likewise the PID controller would automatically for hot,sunny days (when it is hotter outside the heater) and for cold, cloudy days. The analog input (measurement) is called the “process variable” or “PV”. You want the PV to be a highly accurate indication of the process parameter you are trying to control