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PID Controller -A PID controller is an instrument used in industrial control applications to regulate temperature, flow, pressure, speed and other process variables.PID control uses closed-loop control feedback to keep the actual output from a process as close to the target or setpoint output as possible.   The PI, or Proportional and Integral, controller is a commonly used method in control systems to correct for error between the commanded set point and the actual value based on some type of feedback.   Bode Plot  is method in which logarithmic value of magnitude are to be plotted against logarithmic values of frequencies. Logarithmic plots makes it possible to plot wide range of variations on a single paper   Stability from Bode Plot  - Marginally Stable system - GM PM Gain Cross over frequency(ωgc) < Phase cross over frequency (ωpc)   ωgc < ωpc, Gain margin and Phase margin are positive, stable system ωgc > ωpc, G.M. and P.M. negative, unstable...
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PID Tuning Using Ziegler Nichols Method

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  The distinguishing feature of the PID controller is the ability to use the three control terms of proportional, integral and derivative influence on the controller output to apply accurate and optimal control. The block diagram on the right shows the principles of how these terms are generated and applied. It shows a PID controller, which continuously calculates an error value as the difference between a desired setpoint   SP = r(t) and a measured process variable   , and applies a correction based on proportional , integral , and derivative   terms. The controller attempts to minimize the error over time by adjustment of a control variable u(t) , such as the opening of a control valve , to a new value determined by a weighted sum   of the control   terms. In this   model: ·  Term   P   is   proportional   to   the   current   value   of   the   SP − PV   error   e(   t ). For ex...
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