Definitions of Automatic Control Systems Flashcards
Actuator
A device that causes the process to provide the output; the device that provides the motive power to the process.
Actuating signal
Is an error signal determined by the reference selector in a control system that is equal to the difference between the output and input signals.
Closed-loop feedback control system
A system that uses a measurement of the output and compares it with the desired output
Cybernetics
refers to the science in which communication and control
systems in electronic and mechanical devices are studied and compared with those in biological systems. . From the Greek Κυβερνήτης (kubernites) meaning steersman, governor, pilot, or rudder.
Feed forward control system
A mechanism in a system that monitors performance
inputs rather than outputs, and reacts so as to maintain a specified state, thus preventing or minimizing problems before they occur. E.g. cooling of the skin can start a shivering response thus minimizing the extent of shivering
needed.
Gain
The ratio of the system output to the input
Negative feedback control
occurs when the output of a system acts to oppose changes to the input of the system; with the result that the changes
are attenuated. e.g drive car with eyes open, or in physiology, sweating to cool the body following an increase in body temperatures
Open-loop control system
A system that utilizes a device to control the process without using feedback. Thus the output has no effect upon the signal entering the process. E.g. drive car with eyes closed.
Positive feedback
sometimes referred to as “cumulative causation”, refers
to a situation where some effect causes more of itself. A system undergoing positive feedback is unstable, that is, it will tend to spiral out of control as the effect amplifies itself.
Technically, a system exhibiting positive feedback responds to perturbation acts to increase the magnitude of a perturbation. That is, “A produces more of B which in turn produces more of A”.
e.g. contractions in childbirth. When a contraction occurs, the hormone oxytocin is released into the body, which stimulates further contractions. This results in contractions increasing in amplitude and frequency
Proportional control
A proportional control system is a type of linear feedback control system. Two classic mechanical examples are the toilet
bowl float proportioning valve and the fly-ball governor.
The proportional control system is more complex than an on-off control system like a thermostat, but simpler than a proportional-integral-derivative (PID) control system used in something like an automobile cruise control.
An on-off control is like driving a car by applying either full power or no power and varying the duty cycle, to control speed. The power would be on until the target speed is reached, and then the power would be removed, so the car reduces speed. When the speed falls below the target, with a certain hysteresis, full power would again be applied. It can be seen that this looks like pulse-width modulation, but would result in poor control
Proportional Control Theory
In the proportional control algorithm, the
controller output is proportional to the error signal, which is the difference
between the set point (SP) and the process variable (PV). In other words,
the output of a proportional controller is the multiplication product of the
error signal and the proportional gain. This can be mathematically expressed
as:
where
Pout: Output of the proportional controller
Kp: Proportional gain
e(t): Instantaneous process error at time ‘t’. e(t) = SP − PV
SP: Set point
PV: Process variable
Regulator
A device that has the function
of maintaining a designated characteristic. It performs the activity of managing or maintaining a range of values in a machine.
e.g. Examples are a voltage regulator (which can be a transformer whose voltage ratio of transformation can be adjusted, or an electronic circuit that produces a defined voltage), a gas regulator, such as a diving regulator, which maintains its output at a fixed pressure lower than its input, and a fuel regulator (which controls the supply of fuel).
