Automation or automatic control is the strong reduction or even the exclusion of human intervention in various industrial and technological processes associated with manufacturing, design, scientific research, extraction of minerals, the control of machinery, processing and gathering information, etc. Automation includes not only technical equipment and electronic devices but also systematic, statistical and mathematical methods for controlling machines and processes. In modern times the applied computational methods copy the neurological and mental functions of humans.
To automate a process it is necessary to have a source of information (e.g. a sensor), a tool for processing information (a processor, a chip), a control device (controller), an actuator and feedback. This total of mechanisms is perceived in its entirety and is called a system. Automation aims at freeing people from taking part in many production processes and other hard, dangerous or monotonous activities. Automation is considered to be part of the scientific and technical progress, because it increases labor productivity and product quality and reduces cost.
The main types of automation systems are the following:
Automation system for prognosticating and planning;
Automation system for research and experimentation;
Automation system for designing new products;
Flexible automation systems for production;
Automation system for controlling technological processes;
Automation system for controlling machines and devices.
In automation systems, the role of humans is limited to choosing an algorithm for the machine, selecting the input data and analyzing the results.
Human intervention is also required in case of accidents, unplanned situations and the necessity of solving unusual tasks. In other words, humans have the role of analysts, and thinkers, they are the creative unit in the system.
Automation is impossible without computerization, informatics, electronics and robotics. Notwithstanding the achievements of automation, a vast majority of industrial processes and the extraction of raw materials can be conducted only by humans. Still no computer or electronic device can compete with humans in terms of the level of sensory and logical perception, recognition of logical patterns, awareness of reality, resourcefulness and judgment. In other cases, human labor is more cost effective than the complicated, time consuming and costly process of automation.
Automation is used as early as the beginning of the twentieth century in central telephone exchanges, starting with the automatic switchboard, initially operating on the basis of vacuum lamps, then uses switching relays and finally becomes the foundation of the invention of computers. Other first achievements of automation are in the production of paper and rolled metal. The newly introduced controllers and relays accelerate the production process and drastically reduce production costs. Automation soon enters the lifestyle of people by automating the processes of customer service in restaurants. Some restaurants use conveyor belts for serving food directly at the customer’s tables, others use coffee machines and vending machines.
Department stores also began using the principles of automation in the arrangement of goods and self-service. Nowadays, we even have developed online shopping, where the need of a physically existing shop is eliminated. Goods from the store go directly to the client, as is in Vikiwat’s online store.
The main components of automated systems are:
counters (pulse and hour, electromechanical or electronic);
sensors (Hall-effect sensors, inductive sensors, capacitive sensors, magnetic sensors, optical sensors, temperature sensors, ultrasonic sensors, humidity sensors, etc.); joysticks; solenoid valves; thermostats; limit and mechanical position switches; level controllers for liquids; timers and time relays; signal console lamps and means of transportation; alarm signals (sirens, bells, etc.), thermal controllers; photoelectric switches; frequency inverters; hydraulic and pneumatic switches, taps and valves; pressure switches; contact and indicator gauges; electronic auxiliary equipment.
Pulse and hour counters
Counters are devices which are used for regulating, controlling and automating production processes, production lines, etc. Counters are basically of two major types – electromechanical and electronic.
Pulse counters work by means of mechanical contact – a button or other mechanism, or using an electronic sensor. They operate in collection pulse mode.
Upon reaching a certain number of pulses, set by a BCD encoder, the device switches on or off a mechanical switch. It can be reset electronically or mechanically.
Hour counters run in accumulation time mode. The accumulated time appears on a display. The counting begins immediately after the submission of input voltage. It can be used for counting the operating hours of various machines and equipment. Some of the hour counters don’t have reset option.
1. Hall-effect sensors.
They are contactless key switches based on the effect of Hall. They represent a converter that varies its output voltage in response to a magnetic field. Hall-effect sensors are often used in the automotive industry, where they help to make engines more environmentally friendly, thanks to a complete burning-out of the fuel mixture. They can be linear, trigger and switches. In linear Hall sensors the output signal, which is voltage, is proportional to the intensity of the magnetic field.
The various designs can be with or without a permanent magnet. This type of Hall sensors are used for precise contactless measurements of stationary positions or movements. Hall sensors – switches – find application in computer fans and in automotive industry. They have a mounted trigger which provides „1“ at its output at high voltage and „0“ at low voltage. They are also used as terminal switches or for measuring speed.
Hall-effect trigger sensors also work in switch mode, having an output signal „1“ at high magnetic field, but don’t go to state „0“ at low field. To do so, the power of the sensor has to be turned off. They are used in automotive industry. Hall-effect sensors can not be repaired because the electronics is inextricably connected with the plate, which shows the Hall effect.
2. Inductive sensors.
Inductive sensors are used for controlling movable components in production, tracking the number of details and products, defining rates and speed, remote monitoring of machine vibrations, controlling elements such as shafts, bearings, bushes. They are electronic devices reacting when metal objects approach their active surface, generating digital or analog output signal that opens or closes an electrical circuit.
The lack of mechanical contact provides the inductive sensor with long life and high reliability. The basic parameters of inductive sensors are:
switching distance – the distance between the active surface of the sensor and the metal object.
response – the difference in the time for changing the distance from the sensor to objects and the time of galloping motion of the output signal.
hysteresis – the difference in the distances of switching the sensor on and off.
There are various types of inductive sensors. According to the supply voltage there are AC and DC sensors. There are sensors for inclination, self-learning inductive sensors, linear inductive sensors, sensors with microprocessor control, etc.
3. Capacitive sensors.
Capacitive sensors are used in industrial systems for tracking the number of parts, regulating the level of liquids, as a proximity sensor for the motion of objects, just like inductive sensors. The difference is that capacitive sensors can control an object which may not be metallic. Capacitive sensors detect water, glass, plastic, oils, etc. A capacitive sensor contains a capacitor, two coaxial electrodes and a RC generator.
4. Magnetic sensors.
Magnetic sensors respond to changes in the magnetic field. They are activated upon increasing of the magnetic field and open or close an electric circuit. Magnetic sensors are used for guarding and locking of window openings, doors and hatches. They also provide access control to secure sites and warehouses. They can work remotely or through a magnetic chip or a card. They often combine with alarm systems.
5. Optical sensors.
Optical or photoelectric sensors react to changes in a light beam without physical contact between the sensor and the controlled object. The light beam can be in the visible or infrared spectrum. Optical sensors are used for security and access control to various objects, in the automation of production processes, for registering objects on industrial conveyor belts, for creating invisible barriers to provide safety for workers when working with dangerous machinery, packaging and labeling of products, etc. Optical sensors, based on their principle of action, are divided into:
– Optical barrier sensors. They are composed of a transmitter and a receiver in two separate housings located opposite to each other. The transmitter generates and emits a constant light beam towards the receiver. The sensor is activated when the light beam between them is intercepted. These sensors operate in the infrared part of the spectrum.
– Optical diffuse sensors. The transmitter and the receiver are located in a single housing. The transmitter generates and emits a light beam which is reflected by a stationary object and a small part of it goes back to the receiver. When a beam is intercepted, the receiver changes its working mode and activates the electric circuit at the output. Diffuse optical sensors work with infrared rays as well.
– Optical marker sensors. The emitter and the receiver are in a single housing and work in the visible part of the spectrum. These sensors are used for tracking colored markers on colored or transparent basis. They are used in production processes of products moving along conveyor belts.
6. Temperature sensors.
Temperature sensors work mainly according to the principle of thermocouples. Thermocouples are temperature sensors, which consist of two different conductors, responding to temperature in different ways and as a result they generate voltage, proportional to the difference in the temperature between both terminals of the wires. In physics, this is called a thermoelectric effect. Depending on the material of the wires, thermocouples are divided into several types:
– Type K thermocouple. It can be seen in two varieties – chromel – an alloy of nickel and chromium in proportion 90 to 10 and alumel – an alloy of 95% nickel, 2% aluminum, 2% magnesium, and 1% silicon.
– Type J thermocouple. This type has relatively low sensitivity – lower than the sensitivity of thermocouple type K. The material is an alloy of iron and constantan.
– Thermal resistor platinum 100. It is an alloy of rare metals and platinum. This type of temperature sensor has high accuracy. Its main parameter is that at 0°C it has a resistance of 100 Ohm.
Temperature sensors for industrial use are actually thermocouples, enclosed in a metal housing, which serves to measure the temperature of different processes, premises, objects or containers. They are also called thermistors and serve as tactile elements in automation systems by submitting feedback to the thermal controllers and control devices.
In addition to Pt100, there are other thermal resistors, their basic feature being their thermal dependence. They are divided into two types:
– NTC (negative temperature coefficient). This is a thermal resistor (thermistor) with a negative temperature coefficient. It is a semiconductor with negative temperature dependence, i.e. with temperature rise, the resistance of NTC thermistor decreases. The reason for the increase in temperature may be the heating component of the current, flowing through the semiconductor or increase in the ambient temperature.
– PTC (positive temperature coefficient). The resistance of this thermistor increases, when the temperature rises.
Thermistors are used for measuring the temperature, for limiting and stabilizing the current in electronic circuits or for compensating the temperature in transistor circuits.
7. Ultrasonic sensors
Ultrasonic sensors have the following advantages: high accuracy and fast response, simple structure, resistance to shock and vibration, lack of mechanical contact, they work in a wide range of temperature and pressure.
The principle of operation of a standard ultrasonic sensor is as follows: a transmitter, built into the sensor, emits short ultrasonic pulse and simultaneously starts a timer, which gives the time. When the pulse is reflected in the observed object and returns to the sensor – the timer stops. The time between the transmitted and the reflected pulse is used for calculating the distance to the subject. At a repeated pulse – it is compared with the time of the previous pulse and we can analyze the extent of movement of the object.Very often the output signal is a voltage which varies when the object moves or the movement of an object within the area of sensitivity of the sensor proportionally changes the output current. Ultrasonic sensors can be used for controlling all kinds of liquids, including explosion-risk and inflammable ones, conductive and non-conductive, in indoor and outdoor tanks. They are used to measure the distance to granules, bulk materials, transparent and opaque surfaces.