Automatic Control Systems: Types and Components
Automatic: All have a similar structure: a sensor, a controller, and a trigger.
A sensor measures a physical quantity like temperature. Sensors capture information from the environment and are used to measure physical quantities, such as velocity or temperature.
A controller circuit uses the information provided by the sensor to activate or deactivate a radiator, for example. The controller in an automatic system can be anything from a simple electrical circuit to a computer.
A trigger is responsible for carrying out the action for which the automated system was designed. In our radiator example, the radiator itself would be the trigger. Triggers are usually motors, lights, etc.
A control system is a set of interconnected elements used to automate a machine or process. The input (E) is the information the system receives (e.g., the level of light). The output is how the system responds to this information (e.g., the resulting illumination).
Open and Closed Loop Control Systems
- Open-loop control system: The system operates without considering the state of the output.
- Closed-loop control system: The output is compared with the input to correct any errors caused by disturbances affecting the system.
Types of Sensors
Position sensors: These include mechanical switches, magnetic proximity switches, optical position sensors (LDR, photodiodes, and phototransistors), and other position sensors (based on magnetic properties).
Electromagnetic Systems
Electromagnetic systems are based on activating a device by moving parts.
Limit switches: These can be used as controllers in automatic systems to activate other devices. For example, they can control the liquid level in a water reservoir.
Relays: A relay consists of a coil and a movable metal piece attached to contacts. When an electric current passes through the coil, it behaves like a magnet and attracts the metal piece, which changes the position of the contacts.
Programmed Control Systems
Programmed control systems use devices that can store a program internally. To change the operation, it’s not necessary to modify the circuit; you just need to change the program instructions.
Control via a PC: A controller card allows the computer to communicate with the robot being controlled. With this card, the computer receives data from the robot’s sensors and, in turn, controls its motors, lights, or other actuators.
Robots and Microcontrollers
A robot is an automatic machine that can capture information from its environment and react to it. It can also be programmed to perform various tasks.
Microcontroller: These are small, miniature computers embedded in an integrated circuit.
Pneumatic and Hydraulic Circuits
Pneumatic circuits use air, and hydraulic circuits use mineral oil.
Advantages:
- Air is abundant, can be stored, and is clean.
- Oil is resistant to corrosion, has lubricating properties, and is incompressible.
Fluid: Includes both liquids and gases. They don’t have a fixed shape but take the shape of their container.
Mineral: Obtained by the distillation of petroleum and coal tar.
Pressure: Force exerted per unit area: P = F / S (Force = Pressure x Area). Pressure is expressed in pascals (Pa).
Elements of Pneumatic and Hydraulic Circuits
- Power generator element: In an electrical circuit, this is the battery; in a pneumatic circuit, it’s the compressor; in a hydraulic circuit, it’s the pump.
- Transport elements: These connect the circuit elements. In electrical circuits, these are cables; in pneumatic and hydraulic circuits, these are pipes through which the fluid circulates.
- Actuators: Receptors that transform the received energy into another type of energy to perform an action. Examples include lamps in electrical circuits and cylinders in pneumatic and hydraulic circuits.
- Control elements: These open or close the circuit. Examples include switches in electrical circuits and valves in pneumatic and hydraulic circuits, which allow or prevent the movement of the fluid.
Flow Rate: The amount of fluid passing through a section of the circuit per unit of time. It is measured in l/s (Q = Fluid Volume / Time).