Process Controllers

7/29/2019 Process Controllers

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Simulation of Process Control

Loop using DiscontinuousControllers


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Simulink Model of a first-order process loopunder an on-off controller with hysteresis


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The Relay block allows its output to switch between two specified values.

When the relay is on, it remains on until the input drops below the value of the

Switch off point parameter. When the relay is off, it remains off until the input

exceeds the value of the Switch on point parameter. The block accepts one input

and generates one output.

The Switch on point value must be greater than or equal to the Switch off point.

Specifying a Switch on point value greater than the Switch off point models

hysteresis, whereas specifying equal values models a switch with a threshold at

that value.

When the initial input falls between the Switch off point and Switch on point

values, the initial output is the value when the relay is off.


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Simulink Model of a first-order process loopunder an on-off controller with dead zone


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The Dead Zone block generates zero output within a specified region, called its

dead zone. You specify the lower limit (LL) and upper limit (UL) of the dead

zone as the Start of dead zone and End of dead zone parameters, respectively.

The block output depends on the input (U) and the values for the lower and

upper limits:

Input Output

U >= LL and U UL U UL

U < LL U LL


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Simulation of Process Control Loopusing Continuous Controllers


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Regulatory Control with Step Disturbance for P Controller


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Regulatory Control with Sinusoidal Disturbance for P Controller


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Servo Control with Step set point for P Controller


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Servo Control with Sinusoidal set point for P Controller


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Regulatory Control with Step Disturbance for PI Controller


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Regulatory Control with Sinusoidal Disturbance for PI Controller


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Servo Control with Step set point for PI Controller


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Servo Control with Sinusoidal set point for PI Controller


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Regulatory Control with Step Disturbance for PID Controller


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Regulatory Control with Sinusoidal Disturbance for PID Controller


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Servo Control with Step set point for PID Controller


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Servo Control with Sinusoidal set point for PID Controller


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Comparisons of multiple P controllers


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Comparisons of P, PI, PID servo controllers (for step point)


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ZieglerNichols tuning method

Control Type Kp Ki Kd

P Ku / 2 - -

PI Ku / 2.2 1.2Kp / Pu -

classic PID 0.60Ku 2Kp / Pu KpPu / 8


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Z-N tuned PID control

For Process Transfer Function= 6/(48*s^3 + 44*s^2 + 12*s + 1 )

MATLAB code for Z-N tuning method


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MATLAB code for Z N tuning method

%the below code takes the function input from the user and computes the controller

parameters using ZIEGLER-NICHOLAS method

anum=input('Enter the numerator of function: '); % taking the numerator of process

function as user input

aden=input('Enter the denominator of function: '); % taking the denominator of

process function as user input

sys=tf(anum,aden); % making a transer function from the numerator and denominator

S=allmargin(sys); % extracting the crossover frequency etc of the transfer function

if S.GainMargin ~=Inf % proceeding forward in case the system is closed loop stable

Ku=S.GainMargin;

Pu=2*pi/S.GMFrequency;

in=input('Enter the controller type 1.P 2.PI 3.PID'); % asking the user the type ofcontroller for which he wants to compute the values

if (in==1) % giving output for P only controller

Kp=0.5*Ku

con=tf([Kp], [1])


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([ p], [ ])

elseif (in==2) % giving output for PI controller

Kp=0.45*Ku

Ti=Pu/1.2

Ki=Kp/Ti

con=tf([(Kp*Ti) Kp],[Ti 0])

elseif (in==3) % giving output for PID controller

Kp=0.6*Ku

Ti=Pu/2

Ki=Kp/Ti

Td=0.125*Pu

Kd=Td*Kp

con=tf([(Kp*Ti*Td) (Kp*Ti) Kp],[Ti 0])

else

disp('Incorrect option entered');

end

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Process Controllers