Control system

A control system is a set of devices responsible for managing, ordering, directing or regulating the behavior of another system, in order to obtain the desired results.

In a control system, 4 parts can be identified: Measurement, Action, Control, and Reference.

Every control system measures and does something, the process is carried out by the controllerator who uses programs and references (Set-point).- The references or parameters are the adjustable part of the Software; they are intangible, they cannot be touched, and they need a physical support to be memorized; and the Measurements, Drives and Controllers are the Hardware that can be seen and touched.-

Due to our human nature, it is useful to mention manual control on the one hand and automatic control on the other.

In manual control, a conscious brain intervenes, performs the control, the measurements are the senses, the actions are muscular, and what we call the mind is the software with its references.-

In automatic control the controller is an artificial device; which can be mechanical, electronic, chemical, etc; that he was “programmed” to perform his task based on references; receives the measurements and acts on the actuators.

There are two common classes of control systems, open-loop systems and closed-loop systems. In open loop control systems, the output does not intervene in the control action; while in the closed-loop ones if it is going to be required to know the output to exercise control of the system. A closed loop system is also called a feedback control system.

In general, industrial control systems are used for industrial production processes to control equipment or machines.

Objectives

Control systems must achieve the following objectives:

1. Be stable and robust against disruptions and errors in models.
2. Being efficient according to a preset criterion avoiding abrupt and unreal behaviors.

Classification of control systems

Control systems can be open-loop or closed-loop based on whether or not the control action is independent of the output of the system to be controlled.

Open loop control system

It is that system in which the output has no effect on the control system, this means that there is no feedback from said output to the controller so that it can adjust the control action.

• Example 1: A common "automatic" washing machine, as it performs the washing cycles according to a time base, but does not measure the degree of cleaning of the clothes, which would be the way out to consider.
• Example 2: When making a toast, we place the time we assume enough for the bread to come out with the degree of toast we want, but the toaster cannot decide whether it is already toasted or not.

These systems are characterized by:

• Be simple and easy to maintain.
• The output is not compared to the entrance.
• To be affected by disturbances. These can be tangible or intangible.
• Precision depends on the previous calibration of the system.
• They are effective in automatic control systems

Closed-loop control system

They are the systems in which the control action is a function of the output signal; that is, in closed-loop control systems or control systems with feedback, the output to be controlled is fed back to compare it with the input (desired value) and thus generate an error that the controller receives to decide the action to take. on the process, in order to reduce said error and therefore bring the system output to the desired value. Their characteristics are:

• Be complex and wide in number of parameters.
• The output is compared to the input and to perform system control.
• Be more stable to internal disturbances and variations.

An example of a closed loop control system would be the water heater that we use for bathing

Another example would be a highly sensitive level regulator in a tank. The movement of the buoy produces more or less obstruction in a jet of air or gas at low pressure. This translates into pressure changes that affect the membrane of the stop valve, causing it to open more the closer it is to the maximum level.

Types of control systems

Control systems are grouped into three basic types:

1. Man-made. As the electrical or electronic systems that are permanently capturing signals of the state of the system under their control and that when detecting a deviation from the pre-established parameters of the normal operation of the system, they act through sensors and actuators, to bring the system back to its operational conditions. operating normals. A clear example of this will be a thermostat, which consecutively captures temperature signals. When the temperature drops or rises out of range, it acts by turning on a cooling or heating system.

1.1. Due to their causality they can be: causal and non-causal. A system is causal if there is a causal relationship between the outputs and inputs of the system, more explicitly, between the output and the future values of the input.

1.2. According to the number of inputs and outputs of the system, they are called: by their behavior

1.2.1. From one input and one output or SISO (single input, single output).

1.2.2. With one input and multiple outputs or SIMO (single input, multiple output).

1.2.3. From multiple inputs and one output or MISO (multiple input, single output).

1.2.4. Multiple inputs and multiple outputs or MIMO (multiple input, multiple output).

1.3. According to the equation that defines the system, it is called:

1.3.1. Linear, if the differential equation that defines it is linear.

1.3.2. Nonlinear, if the differential equation that defines it is nonlinear.

1.4.The signals or variables of dynamic systems are a function of time. And accordingly these systems are:

1.4.1. From continuous time, if the model of the system is a differential equation, and therefore time is considered infinitely divisible. Variables of continuous time are also called analog.

1.4.2. Of discrete time, if the system is defined by a difference equation. Time is considered to be divided into periods of constant value. The values of the variables are digital (binary, hexadecimal, etc.), and their value is only known in each period.

1.4.3. Of discrete events, if the system evolves according to variables whose value is known when a certain event occurs.

1.5. According to the relationship between the variables of the systems, we will say that:

1.5.1. Two systems are coupled when the variables of one of them are related to those of the other system.

1.5.2. Two systems are decoupled if the variables of both systems have no relationship.

1.6. Depending on the evolution of the variables of a system in time and space, they can be:

1.6.1. Stationary, when their variables are constant in time and space.

1.6.2. Not stationary, when their variables are not constant in time or in space.

1.7. Depending on the response of the system (output value) with respect to the variation of the system input:

1.7.1. The system is considered stable when any bounded input signal produces a bounded response from the output.

1.7.2. The system is considered unstable when there is at least one bounded input that produces an unbounded response from the output.

1.8. Whether or not the input and output of a system are compared, to control the latter, the system is called:

1.8.1. System in open loop, when the output to be controlled is not compared with the value of the input signal or reference signal.

1.8.2. System in closed loop, when the output to be controlled is compared with the reference signal. The output signal that is brought together with the input signal, to be compared, is called the feedback signal or feedback signal.

1.9. According to the possibility of predicting the behavior of a system, that is, its response, they are classified as:

1.9.1. Deterministic system, when its future behavior is predictable within tolerance limits.

1.9.2. stochastic system, if it is impossible to predict future behavior. System variables are called random variables.

2. Natural, including biological systems. For example, human body movements such as the act of indicating an object, walking or talking. It includes as components of the control system: The senses (Measurements), The muscles (Activations), and the brain in its frontal lobe (Controller).

The brain itself is a complete control system. The inputs, the senses, are processed in its posterior and lateral part, occupying most of the brain mass. The outputs, the muscular movements, are processed in its central part, the motor cortex.- The frontal lobe is the controller of human actions and the mind it is the software of the entire system.-

The brain and mind form a control system, with its 4 parts: Measurement, Action, Control and Reference.

3.

Whose components are man-made and the others are natural. The control system of a man driving his vehicle is found. This system is made up of the driver and the vehicle that becomes an extension of his muscular actions.-

The direction, the destination, that the driver has is the reference of the system, it is the parameter that his mind takes, and with his brain he will carry out the calculations, he will process the signals of his senses and the muscular actions necessary to reach your destiny.-

Another example could be the decisions a politician makes before an election. This system is made up of your brain, your senses, your muscles, and your entire mind. The output is manifested in the promises announced by the politician, the degree of acceptance of the proposal by the population, it is the feedback of the system that will adjust its next actions in search of its objective or reference.-

4. A control system can be pneumatic, electrical, mechanical or of any type, its function is to receive inputs and coordinate one or more responses according to its control loop (what it is programmed for).

5. Predictive control, are the control systems that work with a predictive system, and not active like the traditional one (they execute the solution to the problem before it begins to affect the process). In this way, it improves the efficiency of the process by quickly counteracting the effects.

Other examples: a) Signaling control system: traffic light control.

b) Temperature control system: heating control of a home.

c) Liquid level control system: control of water pumps in a building.

d) Vertical or load transport control system: Control of lifts or hoists, conveyor belts.

e) Component transfer control system: Transfer control of files, documents, multimedia components, etc.

f) Position control system: Movement control of a servomotor.

g) Electrical Power control system: Control of the electrical Power provided.

Characteristics of a control system

1. Control: selection of system inputs so that states or outputs change according to a desired way. The elements are:
   • It always exists to verify the achievement of the objectives set out in planning.
   • Measurement. To control it is essential to measure and quantify the results.
   • Detect deviations. One of the functions inherent in control is to discover the differences between execution and planning.
   • Establish corrective measures. The object of control is to foresee and correct errors.
   • Control factors; Quantity, Time, Cost, Quality. Controller: (Electronic). It is an electronic device that emulates the ability of humans to exercise control. By means of four control actions: compare, calculate, adjust and limit. Process: progressively continuous natural operation or development, marked by a series of gradual changes that happen to each other in a relatively fixed form and that lead to a determined result or purpose. Progressive artificial or voluntary operation consisting of a series of controlled actions or movements, systematically directed towards a determined result or purpose. Examples: chemical, economic and biological processes. Supervision: act of observing the work and tasks of another (individual or machine) who may not know the subject in depth.
2. Input Current Sign: Considered as a stimulus applied to a system from an external energy source for the purpose of the system producing a specific response.
3. Departure Current Sign: Answer obtained by the system that may or may not relate to the response implied by the input.
4. Variable Manipulated: It is the element to which its magnitude is modified, to achieve the desired response. I mean, the process is manipulated.
5. Controlled variable: It is the element you want to control. You can say it's the way out of the process.
6. Conversion: The variations or changes that occur in the variable are generated by receptors.
7. External Variations: These are the factors that influence the action of producing a corrective order change.
8. Energy Source: It is the one that delivers the energy necessary to generate any type of activity within the system.
9. Feedback: Feedback is an important feature of closed loop control systems. It is a sequential ratio of causes and effects between the state variables. Depending on the corrective action taken by the system, it can either support a decision, when a return occurs in the system it is said that there is a negative feedback; if the system supports the initial decision it is said that there is a positive feedback.
10. Phase variables: These are the variables that result from the transformation of the original system to the controlable canonical form. From here you also get the control matrix whose range must be of full order to control the system.

Engineering in control systems

Problems

The problems considered in control systems engineering are basically dealt with in two fundamental steps, such as:

1. The analysis.
2. The design.

That analysis investigates the characteristics of an existing system. While in the design the components are chosen to create a control system that later executes a particular task.

Design methods

There are two layout methods:

1. Analysis design.
2. Synthesis design.

Representation

The representation of problems in control systems is carried out through three basic representations or models:

1. Differential equations, integral, derived and other mathematical relationships.
2. Block diagrams.
3. Graphics in analysis flow.

Block diagrams and flow charts are graphical representations intended to shorten the corrective process of the system, regardless of whether it is characterized schematically or by mathematical equations. Differential equations and other mathematical relationships are used when detailed relationships of the system are required. Each control system can be theoretically represented by its mathematical equations. The use of mathematical operations is evident in all controllers of the type Proportional Controller (P), Proportional Controller, Integral (PI) and Proportional Controller, Integral and Derivative (PID), which due to the combination and superposition of mathematical calculations helps to control circuits, assemblies and industrial systems in order to help improve them.