Page 97 - Dynamics and Control of Nuclear Reactors

8.3 Basic control theory 91

actions must be taken quickly, making it then necessary to fully automate the system.
Such is the case with reactor control.
Some examples of common closed-loop control actions are

• Temperature control in a room using a heater or an air-conditioner. The
thermostat measures the room temperature, compares it with the desired (set
point) temperature, and the error provides a signal to switch on or off the heater or
the air-conditioner.
• Control of automobile motion by the driver. The driver compares (by visual
observation) the heading of the vehicle against the markings on the road and
determines an error. Based on this information, the steering wheel is manipulated
to maintain proper position of the vehicle on the road.
• A wide receiver catching a football thrown by the quarterback. Explain why this
is an example of closed-loop control. How does this differ from hitting a golf ball
towards a target?

8.3 Basic control theory

Controller design and control actions vary from being simple to highly complex.
There are five types of feedback control systems:

• Manual
• On-off
• Proportional
• Integral
• Differential
• Advanced.

Feedback control action uses an error signal, which is the difference between the
desired output (set point) and the actual system output (measured value). The error
signal, e(t), is defined as
ð
ð
Error Signal ¼ Setpoint,X set desired conditionÞ Measurement,X m actual conditionÞ
etðÞ ¼ X set tðÞ X m tðÞ (8.1)
The control system makes use of the error signal to initiate an action by the actuator.

8.3.1 Manual control
In this control action the necessary actuation is performed by a person in the loop.
He/she observes the system’s output and takes control action. This may be based on
the experience and/or the intuition of the person.