Process Control Instrumentation PID CONTROLLER MAPUA INSTITUTE OF

Process Control & Instrumentation PID CONTROLLER MAPUA INSTITUTE OF TECHNOLOGY School of Chemical Engineering & Chemistry

OUTLINE • • Important Concepts Process Time Lags PID Control Algorithms Selection Of Control Action

PROCESS CONTROL • Definition – the physical regulation of a process to maintain a particular process variable as close as possible to a desired value.

4 BASIC COMPONENTS IN A FEEDBACK CONTROL LOOP Operator Set Point (SV) 3. Controller Output Process Variable (PV) 2. Measuring Element 4. Final Control Element Controlled Variable (CV) Load Variable Manipulated Variable (MV) Refining Process (Plant) 1. Process

FEEDBACK CONTROL ALGORITHM • Feedback Control = PID Control OUT(t) = OUTdesign + where OUT · OUT(t) = controller output, 0 - 100% · OUTdesign = design (steady state) controller output · OUT = control adjustment

PID CONTROL ALGORITHM • P = Proportional Control Action • I = Integral Control Action • D = Derivative Control Action

Proportional Control Action • control adjustment is proportional to the magnitude of the error OUT = (Kc)(e) where · OUT = control adjustment, % · Kc = Proportionality Constant (Gain or Sensitivity) · e = ERROR = Set Point (SP) - Process

Integral Control Action • control adjustment is proportional to the time integral of the error t OUT = (Kc)/( I) where (e)dt 0 · OUT = control adjustment, % · I = Integral Time Constant, time

Derivative Control Action • control adjustment is proportional to the rate of change of the error OUT = (Kc)( D)(de/dt) where · OUT = control adjustment, % · D = Derivative Time Constant, time

Types of PID Controller • • P - Proportional Controller PI - Proportional Integral Controller PD - Proportional Derivative Controller PID - Proportional Integral Derivative Controller

P - Proportional Controller OUT(t) = OUTdesign + (Kc)(e) • only one tuning parameter ( Kc ) • there is always an offset = steady state error or permanent deviation between the Set Point and the Process Variable

PI - Proportional Integral Controller t OUT(t) = OUTdesign + (Kc)(e) + (Kc)/( I) (e)dt 0 • eliminates offset • more unstable compared to P Controller • two tuning parameters ( Kc , I )

PD - Proportional Derivative Controller OUT(t) = OUTdesign + (Kc)(e) + (Kc)( D)(de/dt) • faster response • does not eliminates offset • susceptible to noise • two tuning parameters ( Kc , D)

PID - Proportional Integral Derivative Controller t OUT(t) = OUTdesign + (Kc)(e) + (Kc)/( I) (e)dt + (Kc)( D)(de/dt) 0 • faster response • eliminates offset • susceptible to noise • three tuning parameters ( Kc , I , D)

Selection of Control Action