Control Devices: Calibrated Orifice, CAM Timer, Centrifugal Governor, Cineston Controller, Control Panel (Engineering), Control Valves,

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pages: 37. Chapters: Calibrated orifice, Cam timer, Centrifugal governor, Cineston controller, Control panel (engineering), Control valves, Dashpot timer, Digital test controller, Drum sequencer (controller), Electrohydraulic servo valve, Flow computer, Flow control (fluid), Gas flow computer, IQAN, Mass flow controller, Orifice plate, Pendulum-and-hydrostat control, PID controller, Pneumatic flow control, Restrictive flow orifice, Servomechanism, Servo drive, Servo motor, Ship's wheel, Shuttle valve, Solar dial, Sorteberg relay, Stack light, Steering engine, Steering wheel, Street light controller, Subsea valves, Tiller, Ziegler-Nichols method. Excerpt: A proportional-integral-derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems. A PID controller calculates an "error" value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs. The PID controller calculation (algorithm) involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted P, I, and D. Heuristically, these values can be interpreted in terms of time: P depends on the present error, I on the accumulation of past errors, and D is a prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve, a damper, or the power supplied to a heating element. In the absence of knowledge of the underlying process, a PID controller has historically been considered to be the best controller. By tuning the three parameters in the PID controller algorithm, the controller can provide control action designed for specific process requirements. The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the setpoint and the degree of system oscillation. Note that the use of the PID algorithm for control does not guarantee optimal control of the system or system stability. Some applications may require using only one or two actions to provide the appropriate system control. This is achieved by setting the other parameters to zero. A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers are fairly common, since derivative action is sensitive to measurement noise, whereas the absence of an integral ter