Basic elements of automation

Any automatic device consists of interconnected elements whose task is to qualitatively or quantitatively transform the signal they receive.

Automation element — It is part of the device of an automatic control system in which qualitative or quantitative transformations of physical quantities are carried out. In addition to the conversion of physical quantities, the automation element serves to transmit a signal from the previous element to the next.

The elements included in the automatic systems perform various functions and, depending on their functional purpose, are subdivided into perceiving, transforming, executing, adjusting and correcting organs (elements), as well as elements for adding and subtracting signals.

Perceptive organs (sensory elements) are designed to measure and convert a controlled or controlled value of the control object into a signal convenient for transmission and further processing.

Examples: sensors for measuring temperature (thermocouples, thermistors), humidity, speed, force, etc.

Amplifiers (elements), amplifiers — devices which, without changing the physical nature of the signal, produce only amplification, i.e. increasing it to the required value. Automatic systems use mechanical, hydraulic, electronic, magnetic, electromechanical (electromagnetic relays, magnetic starters), electric machine amplifiers, etc.

Transforming organs (elements) converting signals of one physical nature into signals of another physical nature for convenience in further transmission and processing.

Examples: Non-electrical to electrical converters.

Executive bodies (elements) are intended to change the value of the control action on the control object, if the object is one unit with the control body, or to change the input values ​​(coordinates) of the control body, which should also be considered as an element of automatic systems. According to the principle of operation and design, the executive and regulating elements are diverse.

Examples: heating elements in temperature control systems, electrically actuated valves and valves in liquid and gas control systems, etc.

Governing Bodies (Elements) are designed to set the required value of the controlled variable.

Corrective bodies (elements) serve to correct automatic systems in order to improve their operation.

Depending on the functions performed by automation elements, they can be divided into sensors, amplifiers, stabilizers, relays, distributors, motors, etc.

Sensor (measuring body, sensor element) — an element that converts one physical quantity into another, more convenient for use in an automatic device.

The most common sensors are those that convert non-electrical quantities (temperature, pressure, flow, etc.) into electrical ones. Among them there are parametric and generator sensors.

Parametric sensors are those that convert the measured value into a parameter of the electrical circuit — current, voltage, resistance, etc.

For example, a temperature contact sensor converts a change in temperature into a change in electrical circuit resistance from a minimum when the contacts are closed to infinitely high when the contacts are open. This item is a temperature sensor installed in household irons.

Rice. 1. Scheme of regulation of heating temperature by thermal contact

In a cold iron, the thermal contact, which is sensitive to temperature changes, closes, and when the iron is turned on, a current flows through the heating element, which heats it up. When the plate of the iron reaches the contact temperature, it opens and disconnects the heating element from the network.

A generator is called a sensor that converts the measured value into EMF, for example a thermocouple used in conjunction with a voltmeter to measure temperature. The emf at the ends of such a thermocouple is proportional to the temperature difference between the cold and hot junctions.

Rice. 2. Thermocouple device

The device and principle of operation of the thermocouple. The working body of the thermocouple is a sensitive element consisting of two different thermoelectrodes 9 welded together at the end 11, which is a hot junction.The thermoelectrodes are isolated along their entire length using insulators 1 and placed in protective fittings 10. The free ends of the element are connected to the contacts 7 of the thermocouple located in the head 4, which is closed with a cover 6 with a gasket 5. The positive thermoelectrode is connected to a contact with a «+» sign.

The sealing of the thermoelectrode sleeves 9 is carried out using an epoxy compound 8. The working end of the thermocouple is isolated from the protective reinforcement with a ceramic tip, which may be missing in some designs to reduce thermal inertia. Thermocouples may have a nipple 2 for field mounting and a nipple 3 for entering the connecting wires of the meters.

Read more about the classification, device and principle of operation of thermocouples in this article: Thermoelectric converters

Differences between parametric and generator sensors

In parametric sensors, the input signal changes each parameter of the sensor (resistance, capacitance, inductance) and its output signal accordingly. An external power source is required for their operation. Generator sensors generate EMF under the action of the input signal and do not require an additional power source.

Read more about the different types of sensors here: potentiometer sensors, inductive sensors

Other automation elements

Amplifier — an element in which the input and output quantities have the same physical nature but are quantitatively transformed. The amplification effect is achieved by using the energy of the power source.In electrical amplifiers, voltage gain ku = Uout /Uin, current gain ki=Iout/Azin and power gain kstr=ktics are distinguished.

Any electrical machine generator can serve as an amplifier. A small change in excitation in it leads to a significant change in the output signal - load current or voltage. The power source is a motor that drives the generator into rotation.

Examples of amplifiers previously actively used in electric propulsion: electric machine amplifiers, magnetic amplifiers… Currently, amplifiers and converters are actively used for these purposes. thyristors and high switching frequency transistors.

Stabilizer - an automation element that provides an almost constant value of the output value when the input value changes within the specified limits. The main characteristic of the stabilizer is the stabilization coefficient, which indicates how many times the relative change of the input value is greater than the relative change of the output value. Current and voltage stabilizers are used in electrical devices.

Read more about stabilizers here: Ferroresonant voltage stabilizers and Electronic voltage stabilizers

Relay - an element in which, when a certain input value is reached, the output value changes abruptly. Relays are used to fix certain values ​​of the input value, amplify the signal and simultaneously transmit the signal to several electrically unrelated circuits. The most common are various designs electromagnetic control relay.

Distributor — an automation element that provides alternative switching of signal transmission circuits. Distribution is most often used in electrical circuits. An example of a distributor is a step finder.

Engine — a mechanism that converts some energy into mechanical energy. Electric motors are most often used in automation devices, but pneumatic ones are also used. In automation, the most common devices of this type are stepper motors.

Transmitter — a device designed to convert one quantity into another, convenient for transmission over a communication channel. In addition to the main function, the transmitter usually performs encoding of the converted value, which makes it possible to use communication channels efficiently and reduce the influence of interference on the transmitted signal.

Receiver — a device that converts the received signal on the communication channel into a value convenient for perception by the elements of the automation system. If the signal is encoded during transmission, a decoder is included in the receiver. Receivers and transmitters are actively used in telecontrol and telesignaling systems.