QUESTION

QUESTION 2 Process variable - is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range. See also control theory. A servomechanism - sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a car's cruise control uses closed loop feedback, which classifies it as a servomechanism. Feedback - There are many different control mechanisms that can be used, both in everyday life and in chemical engineering applications. Two broad control schemes, both of which encompass each other are feedback control and feed-forward control. Feedback control is a control mechanism that uses information from measurements to manipulate a variable to achieve the desired result. Feed-forward control, also called anticipative control, is a control mechanism that predicts the effects of measured disturbances and takes corrective action to achieve the desired result. The focus of this article is to explain application, advantages, and disadvantages of feedback control. Process set point - A preset value such as a specific speed or position that the control system is supposed to reach. Also known as the target value. Error - The difference between the SP and the PV. When errors are detected, the controller sends instructions to the control system to adjust the output to compensate. Controller and Measurement - 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.