control engr

1. PID Controller using PCUSIM
An Introduction to the Proportional Integral Derivative (PID) Controller using PCUsim interface
to control the machine in manual and automatic mode.
Engr. Owais Awan
Instrumentation and Control Lab
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2. Let’s start with a discussion about home temperature control. If the room temperature is below the setpoint, the
furnace is turned ON. When the room temperature increases above the setpoint, the furnace turns OFF. This type of
control is referred to as ON/OFF or Bang-Bang Control. The temperature is not exactly held at the setpoint of 70°F, but
cycles above and below the setpoint. ON/OFF control may be ok for your house, but it is not ok for industrial processes
or motion control 2

3. Let’s look at an example of tank level control to explain why. The Valve fills the tank as the pump drains it. If the valve
is operated with ON/OFF control, the water will fluctuate around the 50% setpoint. For our purpose, let’s say the
fluctuation is ±10%. In most industrial applications, this fluctuation around the setpoint is not acceptable. 3

4. An Introduction to the Proportional Integral Derivative (PID) Controller using PCUsim interface to control the machine
in manual and automatic mode.
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5. Let’s look at how a PID Controller fits into a feedback control loop. The Controller is responsible for ensuring that the
Process remains as close to the desired value as possible regardless of various disruptions.
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6. The controller compares the Transmitter Process Variable (PV) signal, and the Setpoint. Let’s refer to the difference
between the Process Variable and the Setpoint as the Error signal. Based on that comparison, the controller produces
an output signal to operate the Final Control Element. This PID Controller output is capable of operating the Final
Control Element over its entire 100% range.
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7. The PID controller determines how much and how quickly correction is applied by using varying amounts of
Proportional, Integral, and Derivative action. Each block contributes a unique signal that is added together to create the
controller output signal.
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8. The proportional block creates an output signal proportional to the magnitude of the Error Signal
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9. Unfortunately, the closer you get to the setpoint, the less it pushes. Eventually, the process just runs continuously close
to the setpoint, but not quite there.
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10. The integral block creates an output proportional to the duration and magnitude of the Error Signal
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11. . The longer the error and the greater the amount, the larger the integral output. As long as an Error exists, Integral
action will continue. -
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12. The derivative block creates an output signal proportional to the rate of change of the error signal. The faster the error
changes, the larger the derivative output. 12

13. Derivative control looks ahead to see what the error will be in the future and contributes to the controller output
accordingly. That brings us to a term called Controller Tuning.
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15. End of Lecture
Questions?
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