Within systems theory, a control system or regulatory system is a specialized subsystem that is designed to monitor and regulate the behavior and operation of the broader system it is a part of in order to maintain its functionality. The primary objective of a control system is to preserve the internal level of order that enables the system to function and develop. Within systems theory this preservation of a stable or equilibrium state to a system’s operation is called homeostasis. On its most basic level homeostasis is the maintenance of a system within a given set of parameters or environmental conditions that best enable its internal functioning. Homeostasis is untimely at the core of what all types of control systems are designed to do. Some examples of control systems include the thermostat that is designed to regulate the temperature of a given system, such as a building, within a defined set of parameters. Another example from the human body is the hypothalamus that regulates the autonomic nervous system. It controls basic body functions such as internal temperature, hunger, sleep and so on. The commander of a military unit is another example. He or she is given the position of supreme control within the organization, responsible for its maintenance and operation. A nation’s government is another example of a control system, designed to maintain and develop the socio-economic system within a given jurisdiction.
Control System’s Elements
All of these very diverse systems share a basic underlying set of relations and components that are common to all regulatory systems. There are essentially just three components to any given control mechanism. Firstly, we need a sensor for feeding information into the system. Secondly, a controller that contains the logic or set of instructions for processing this information. Lastly, an actuator that executes some action in order to affect the state of the system or its environment.
Firstly, a sensor is a component that detects and encodes some stimulus from the system’s environment and transfers it to the controller. Any given sensor can of course, only sense a specific stimulus. A sensor has a physical device that is receptive to some change in a parameter that it is measuring, with this change in stimulus then being encoded into information and transferred ultimately to the controller. Examples of this are the visual system within biological organisms where the photons hitting the optical nerves in the retina are encoded into electrical signals to be sent to the brain, or seismometers that sense small movements in the earth’s surface and encode them into graphical representations.
Secondly, the controller. The controller is the brains of the operation. It contains the critical logic that is governing the whole system and is encoded in some set of instructions. The controller can be modeled as an information-processing unit taking in some input of information, manipulating this information according to its set of instructions with the result being an output of information that is designed to be acted upon. An example of a controller might be a digital circuit board composed of logic gates that physically manipulate an electrical input according to binary operations to produce some output signal.
On this basic level, the set of instructions is what we would call an algorithm. By switching gates on and off, they can respond to a limited set of input signals through an if/then logic, to create some output response. This set of logic gates is an example of a very simple controller. To take an example of a much more complex controller we might think about a democratic nation’s public administration system operating under a set of instructions encoded within a constitution. It is designed to take information about the state of the nation that has been received from a number of different sensors such as the mass media or statistics gathering and process this information according to these sets of instructions to produce the policies and regulations required to maintain and develop the socio-economic system of the nation state.
Lastly, the actuator. An actuator is an instrument or set of instruments that act on the instructions produced by the controller. It is designed to physically affect the system that is being regulated in order for it to conform with the instructions produced by the controller. An example of an actuator might be the muscles in the human body. They are controlled by electrical signals sent from the brain. We can actuate them in order to change the state of our environment by simply moving from one location to another. The brakes on a car are another example of an actuator. They execute or act on one’s instructions to regulate the speed of the car.
For a system to be regulated or under control means that for any given change in state presented by its environment the system can generate a response so as to maintain functionality. In order for a system to be able to regulate itself, all of these components to a regulatory system need to be working together. Without a sensor, the controller cannot know the state of its environment, and thus the appropriate response. If you are driving your car with impaired vision, you are not receiving all the required information about your changing environment that is required to generate the appropriate response, with the result being that sooner or later you will fail to receive critical information that will cause an accident, drastically reducing the system’s functionality; thus in such a situation one can say you are not fully in control of the vehicle. Without a controller the system cannot alter an input to a required output, thus cannot adapt, and will be under the control of external influences within its environment. In order for the system to have control over itself, it must have a logical set of instructions that are able to process any input signal to the required output response. There are two key questions to consider here. Firstly, the basic functioning of the logic unit. Are there errors in the instructions and how they are being processed, such as bugs in computer code or random deformations within DNA? Secondly, does the logic have sufficient variety and complexity to be able to represent all the different states that its environment will present it with? Within cybernetics, this is called requisite variety, which simply means that the system is required to have a set of instructions with sufficient variety and complexity to represent all the diverse states within its environment, or else it will not be able to regulate itself within that environment. As an example of this, we might think of asking a small child to run a multi-national corporation. The child simply does not have the conceptual capabilities to represent the complexity of the system it is asked to regulate. Thus, it is not in control and the system’s functionality will be degraded over time as it moves outside of some homeostatic parameter that the child is not aware of and thus not able to respond to. Thirdly, without the functioning of the regulatory system’s actuator, the instructions created by the logic unit cannot be executed upon and thus the system cannot alter its state to respond to the changes in its environment. If a nation’s law enforcement agency refuses to execute on a court’s legal decree to disband a popular protest, then the government is essentially out of control, as it no longer has the actuator required to regulate the system.
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