Getting Started: Control and Automation

The act of carrying out control functions refers to the process that takes place within a system, which has as its antecedent that one or more input magnitudes (physical variables found in the environment) affect and manipulate in turn a series of output magnitudes, all this, from a control logic that implicitly entails actions under the principle of "intrinsic safety" that is inherent to the system.

When a sequence of steps is established to perform a specific task based on data obtained from the environment, the goal is for the process or system to be self-regulating. Once this is achieved, the process is considered automated, and one of its main applications is assisting humans with tasks related to accuracy, speed, and safety.

Any "automatic" control system must be stable; this is a primary requirement. The concept of ideal stability, considered absolute, refers to a control system where responses are completely immediate to manipulation of the system's input variables. However, in reality, a system must possess reasonable relative stability; that is, the response speed must be reasonably fast (according to the sensors and actuators used) and it must exhibit a good degree of flexibility. In addition to the above, a control system must have the capacity to reduce to zero a sufficiently small value derived from any error margins that may arise.

Figure 1.1 Automatic Control System.

Essentially, the existing technologies for establishing an automatic control system are oriented towards the concepts called "Dedicated or Standard Automation" and "Flexible Automation".

DEDICATED OR STANDARD AUTOMATION

The representative elements of this technology are the so-called electromechanical relays, which, once installed, make it undesirable to carry out modifications to their operating logic, due to how problematic and conflictive it is to change the design of a control system.

Electromechanical relays consist of a coil that, when its terminals are energized, produces a magnetic field, which in turn causes a series of moving contacts to close or open, interrupting or allowing, respectively, the passage of electric current through them; taking into account this way of acting, an electromechanical relay has two operating states, one when its coil is without energy (equivalent to logic 0) and when its coil is energized (equivalent to logic 1).

The state of the contacts of electromechanical relays can branch out to many other locations, thus affecting various points along the control circuit. Taking advantage of these characteristics, electromechanical relays, through their contacts, power the coils of other relays; that is, they control other relay blocks, which, when grouped into circuits, perform the logical operations of the automatic control system.

Figure 1.2 Relay frame

FLEXIBLE AUTOMATION

Control systems that operate under this philosophy base their decision-making on the execution of coded instructions, which are stored in a memory circuit and interpreted by a microprocessor or microcontroller. The key advantage of flexible automation is that if it becomes necessary to modify the control system, it is sufficient to change the coded instructions.

Figure 1.3 Electronic Controls. Flexible automation consists of a Programmable Logic Control (PLC) system capable of processing binary signals based on a user-defined program. This system includes input, output, and data transmission ports with the necessary interaction for its operation. In this way, mechanical sequences or manufacturing processes can be directly controlled using the input and output signals. The fields where a PLC system can be applied are virtually countless. These control systems are primarily intended for "process control" functions, ensuring that each step or phase of the process is carried out in the correct and synchronized chronological order that has been previously established. A PLC system is based on a specific type of computer, designed for work environments where its primary mission is the control of industrial processes, which may consist of various types of machinery, robots, assembly lines, etc.  

Figure 1.4 Automated process. A PLC may often have a keyboard as a data input device, but the programmable logic controller will only respond to its control actions based on the information provided by its sensors. Furthermore, the control activities performed by the PLC during operation can be monitored in detail using a monitor or printer. Depending on the actual situation requiring a response, the internal configuration of the PLC can have a high or low degree of complexity, regardless of the complexity of the application. A PLC consists of the following essential components:   Hardware.This refers to all the electronic components that make up the control system. Its main function is to activate or deactivate the controls that manipulate all the connected power elements, all according to a specific logical sequence. The most important hardware component is the microprocessor or microcontroller.   Software.This is the intangible part that has no physical counterpart, as it consists of the programs that determine how the control system operates. In other words, these are the instructions that generate the commands governing the electronic components. The programs are stored in memory, which can be accessed to execute the instructions. When either the order or the instructions that make up the program are modified, the execution sequence of the control system is invariably altered, even if this modification does not involve a change in the hardware.   Sensors.These are devices that interpret the physical variables found in the environment, convert them into electrical signals, and finally communicate them to the PLC. This information represents the state of the process being controlled.   Actuators.- To have the ability to modify the physical variables that are important within a process, power elements known as actuators are used.   Programmer.This is the means by which the software instructions are ordered and subsequently stored in the PLC. Currently, this process can be carried out using a personal computer, which in most cases also serves to verify the control system programs.