It has long been known that most high-end industrial applications have relays for efficient operation. Relays are simple switches that operate both electrically and mechanically. They consist of a set of contacts and an electromagnet, due to which the switching mechanism is implemented. There are other operating principles that differ depending on their application. What types of relays are there?
Why is it so effective?
The main relay operations take place in places where only a low power signal can be supplied. This device is also used in places where multiple circuits must be controlled by a single signal. Their use began during the invention of telephones, which played an important role in switching calls at telephone exchanges. They were also used to transmit telegrams over long distances.
After the invention of computers, they helped in performing various logical operations using signals.
"Design"
The relay has four main parts:
- iron core;
- movable reinforcement;
- control coil;
- contact point switch.
The image above shows the design of the relay.
This is a wired coil electromagnetic relay surrounded by an iron core. For movable armature (armature), as well as for switch contacts, a path with a very low resistance to magnetic flux is provided. The movable armature is connected to the yoke, which is mechanically connected to the contacts of the switch. These parts are held securely by a spring. It creates an air gap in the circuit when the relay is de-energized.
Principle of operation
The function can be better understood by studying the following diagram above.
The diagram shows the relay elements and how they are used. The iron core is surrounded by a control coil. As shown, the power source is supplied to the electromagnet through a control switch and through the contacts. When the current begins to move through the control coil, the electromagnet is charged, which allows you to strengthen the magnetic field.
Thus, the upper contact arm begins to be attracted to the lower fixed bracket, causing a short circuit for power. On the other hand, if the relay was already de-energized when the contacts were closed, then they move in the opposite direction and close the circuit.
As soon as the coil current is disconnected, the movable reinforcement will be returned by force back to its original position. This power will be almost equal to half the magnetic force. This is the main purpose and principle of the relay.
In the relay, the types of operations are divided into two main ones. One of them is the use of low voltage. For applications with low voltage, preference will be given to reducing noise throughout the circuit. And for high voltage operations, noise should be reduced by sparking.
The history of the first relays
In 1833, Karl Friedrich Gauss and Wilhelm Weber developed an electromagnetic relay. But the American scientist Joseph Henry often claimed that he invented the relay in 1835 in order to improve his version of the electric telegraph, developed earlier in 1831.
It is claimed by some that the English inventor Edward Davy "definitely invented the electric relay" in his electric telegraph c 1835.
Also a simple device, now called a relay, was included in Samuel Morse's original telegraphic patent of 1840.
The described mechanism acted as a digital amplifier, repeating the telegraph signal, thus allowing the signals to propagate as far as necessary. The word appears in the context of electromagnetic operations since 1860. And what are the types of electromechanical relays?
Coaxial relay
Often, a coaxial relay is used as a TR (transmit-receive) repeater, which switches the antenna from receiver to transmitter. This protects the device from high power.
It is often used in transceivers that combine the transmitter and receiver in one device. The contacts are designed so as not to reflect any radio frequency power back to the source, but to provide a very high isolation between the terminals of the receiver and transmitter. The characteristic impedance of the relay is matched to the transmission line of the system impedance, for example, 50 Ohms.
Relay voltage 220V for home
Relays for home use most often. It is necessary to secure all connected devices. Increasing or decreasing the voltage of the input network can adversely affect the operation of the devices. This security mechanism notices these leaps and prevents access to the network.
The principle of operation of this relay is based on voltage measurement. If it exceeds or reduces the permissible norm, the relay contacts close for a certain time, and then open again. But relays have different types.
Power relay
This relay has contacts that are mechanically connected to each other (Mechanical relay), therefore, when the coil is energized or de-energized, all connections move together. If one set of contacts becomes stationary, no other contacts can move. The function of the power contacts is to enable the safety circuit to check the condition.
Forced-controlled contacts are also known as “positive-controlled contacts,” “captive contacts,” “locked contacts,” “mechanically connected contacts,” or “safety relays.” These safety relays must comply with the design and manufacturing rules that are defined in one basic machinery standard EN 50205 - relays with forcedly controlled (mechanically connected) contacts.
These rules for safety design are defined in EN 13849-2 Relay Classification as Basic Safety Principles and Verified Safety Principles, which apply to all devices. Forced contact relays are manufactured with different sets of main contacts - NO, NC, or "Switching".
Use for machine logistics
The relay machine is standardized for industrial control. They are characterized by a large number of contacts (sometimes expandable in the field), which can easily be transferred from a normally open state to a normally closed state, easily replaced by coils and a form factor that allows compact installation of many relays on the control panel. Although such panels were once the foundation of automation in industries such as automobile assembly, the programmable logic controller (PLC) has largely supplanted relay machines from serial control applications. In relays, machine types are of great importance.
It allows you to switch circuits using electrical equipment. For example, a timer circuit may switch power at a given time. For many years, relays have been the standard method of controlling industrial electronic systems. Several devices can be used together to perform complex functions (relay logistics). The principle of relay logistics is based on mechanisms that energize and deenergize related contacts.
Motor protection
Electric motors need protection against power overload, otherwise their winding may begin to melt with the risk of a fire. Overload sensitive devices are a thermal relay in which a coil heats a bimetallic strip or melts in solder to operate auxiliary contacts. These auxiliary contacts are located in series with the coil of the motor contactor, so they turn off the motor when it overheats.
This thermal protection is relatively slow, allowing the motor to consume higher inrush currents until the protective function is activated. When it is exposed to the same ambient temperature as the engine, a useful, albeit crude, compensation of the engine temperature is provided.
Another common overload protection system uses an electromagnetic coil built in series with the motor circuit. This is similar to a control relay, but requires a fairly high fault current to control the contacts. To prevent short circuits arising from surges. The movement of the armature is damped using the dashboard.
Thermal and magnetic overload detection are commonly used together in a motor protection relay. Electronic overload relays measure the current of the motor, and can estimate the temperature of the winding using the “thermal model” of the armature system, which can be configured to provide more accurate protection.
Some motor protection mechanisms include temperature sensor inputs for direct measurement from a thermometer integrated in the winding.
What you need to know when choosing a relay?
You should note some factors when choosing a particular relay.
- Protection - it should be noted various means of protection, for example, from touching the coil. It helps reduce sparking in circuits with inductors. It also helps to reduce the overvoltage that occurs when signals change.
- Look for a standard relay with all official permissions.
- Switch time - you can use the high speed version.
- Ratings - Current ratings range from a few amperes to 3000 amperes. For rated voltages, they range from 300 watts of alternating current to 600 watts of alternating current. There is also a high voltage version (about 15,000 volts).
- The type of contact used is NC, NO, or closed contact.
- Depending on your goals, you can choose the types of chains: “Make to break” or “Break to smart contact”.
- Pay attention to the insulation between the coil circuit and the contacts.
There is also a 220V voltage relay for the home, so you should study the work circuits and connection types.