It has long been known that most high-end industrial applications have relays to work efficiently. Relays are simple switches that operate both electrically and mechanically. They consist of a set of contacts and an electromagnet, thanks to which the switching mechanism is carried out. There are other principles of operation that differ depending on their application. What types of relays are there?
Why is it so effective?
The main operation of the relay occurs in places where only a low power signal can be applied. 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 send telegrams over long distances.
After the invention of computers, they helped to perform various logical operations using signals.
Design
The relay has four main parts:
- iron core;
- movable armature;
- control coil;
- common ground switch.
The image above shows the design of the relay.
This is an electromagnetic relay with a wire coil surrounded by an iron core. For the movable armature (armature) as well as for the switch contacts, a path with very low magnetic flux resistance is provided. The movable armature is connected to a yoke, which is mechanically connected to the switch contacts. These parts are securely held by a spring. It creates an air gap in the circuit when the relay is de-energized.
Working principle
The function can be better understood by examining 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, power is supplied to the electromagnet through the control switch and through the contacts. When the current begins to flow through the control coil, the electromagnet is charged, which allows the magnetic field to be strengthened.
Thus, the upper contact arm begins to be attracted to the lower fixed bracket, causing a short circuit to 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 complete the circuit.
As soon as the coil current is cut off, the movable armature willforcefully returned to its original position. This power will be almost equal to half the magnetic force. This is the main purpose and principle of operation 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 the application of low voltage operations, preference will be given to reducing the noise of the entire circuit. And for high voltage operations, the noise must be reduced by sparking.
History of the appearance of the first relays
In 1833 Carl Friedrich Gauss and Wilhelm Weber developed the electromagnetic relay. But the American scientist Joseph Henry often claimed that he invented the relay in 1835 to improve his version of the electric telegraph, developed earlier in 1831.
It is claimed by some that the English inventor Edward Davy "certainly invented the electrical relay" in his electrical telegraph c. 1835.
Also, a simple device now called a relay was included in Samuel Morse's original 1840 telegraph patent.
The mechanism described acted as a digital amplifier, repeating the telegraph signal, thus allowing the signals to travel as far as needed. The word has been appearing in the context of electromagnetic operations since 1860. What are the types of electromechanical relays?
Coaxial relay
Often a coaxial relay is used as a TR (transmit-receive) repeater that switchesantenna from receiver to transmitter. This protects the device from high power.
It is often used in transceivers that combine a transmitter and receiver in one device. The pins are designed not to reflect any RF power back to the source, but to provide very high isolation between the transmitter and receiver terminals. 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 the home are most often used. 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 protection mechanism detects these spikes and prevents access to the network.
The principle of operation of this relay is based on voltage measurement. If it exceeds or lowers the allowable rate, the relay contacts close for a certain time, after which they open again. But relays have different types.
Power contacts relay
This relay has contacts that are mechanically connected to each other (Mechanical Relay), so when the coil is energized or de-energized, all connections move together. If one set of contacts becomes stationary, no other contacts will be able to move. The function of the power contacts is to allow the safety circuit to check the status.
Forced operated contacts are also known as positivecontrol", "captive contacts", "interlocked contacts", "mechanically linked contacts" or "safety relays". These safety relays must comply with the design and construction rules that are defined in one major machinery standard, EN 50205, relays with force-guided (mechanically linked) contacts.
These safety design rules are defined in EN 13849-2 "Relay Classification" as "Basic Safety Principles" and "Tested Safety Principles" which apply to all devices. Forced operated contact relays are available with different sets of main contacts - NO, NC or "Changeover".
Use for machine tool logistics
The relay machine is standardized for industrial control. They feature a large number of contacts (sometimes expandable in the field) that are easily converted from normally open to normally closed, easily replaceable coils, and a form factor that allows multiple relays to be compactly mounted on a control panel. While such panels were once the backbone of automation in industries such as automotive assembly, the programmable logic controller (PLC) has largely displaced relay machine tools from serial control applications. In a relay, machine types matter a lot.
It allows you to switch circuits with electrical equipment. For example, a timer circuit may switch power tospecified time. For many years, relays have been the standard method for 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 de-energize the associated contacts.
Motor protection
Electric motors need protection against power overload, otherwise their windings may start to melt, risking a fire. Overload sensitive devices are thermal relays in which a coil heats a bimetallic strip or melts into solder to operate the auxiliary contacts. These auxiliary contacts are in series with the motor contactor coil, so they cut the motor off when it overheats.
This thermal protection operates relatively slowly, allowing the motor to draw higher starting currents before the protection function operates. When exposed to the same ambient temperature as the engine, a useful, albeit crude, engine temperature compensation 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 drive the contacts. To prevent short circuits due to current surges. Anchor movement is damped by the instrument panel.
Detectionthermal and magnetic overload are commonly used together in motor protection relays. The electronic overload relays measure motor current and can estimate winding temperature using a "thermal model" of the armature system, which can be tuned to provide more accurate protection.
Some motor protection mechanisms include temperature sensor inputs for direct measurement from a thermometer built into the winding.
What you need to know when choosing a relay?
You should note some factors when choosing a particular relay
- Protection - various means of protection should be noted, for example, from touching the coil. It helps reduce sparking in circuits using inductors. It also helps to reduce the overvoltage caused by changing signals.
- Look for a standard relay with all official approvals.
- Switch time - you can use the high speed version.
- Ratings - current ratings range from a few amps up to 3000 amps. In the case of nominal voltages, they range from 300 W AC to 600 W AC. There is also a high voltage version (about 15,000 volts).
- Type of contact used - NC, NO or closed contact.
- Depending on your goals, you can choose the types of circuit: "Make to Break" or "Break to Smart Contact".
- Note the insulation between the coil circuit and the contacts.
Also a 220V voltage relay for the home, so you should study the working diagrams and connection types.
