Relay | Structure of Relays and Operating Principles | ElectGo

Relays are the special case of switches which are electromagnetic switches. With the help of the relays, a low-powered electrical signal is used to control the ON and OFF state of a circuit. It is used in different circuits for different purposes from which the switching purpose is the main concern.

There are different categories of relays depending upon the structure and the operation of the relay. However, a general relay structure of a relay comprises the following parts.

Electromagnet

• The electromagnets used in the relays are made up with the help of the coil. The coil wire is wrapped in a core of soft iron. The soft iron core is used for the path for magnetic flux. As the name suggests electromagnetic relay works on the electromagnet. 

Moveable Armature

• The moveable armature is used in contact with the electromagnet. The complete working of the relay is dependent on the electromagnet used in the relay and the moveable armature. When the electromagnet is forced to perform its operation due to any overload condition or the predefined condition as per the operation of the relay, the moveable armature is used for connection purposes or contact purposes. 

Switch Point Contacts

• The switch point contacts in a relay are used for switching purposes. There are basically switch points in a general relay. With the help of the switch points, the switching operation of the relay is performed.

Spring

• The above-mentioned components in the structure of the relay are held together at their fixed position with the help of the spring. The spring can be adjusted for the switching purpose of the relay.

From the very beginning of the modern era, relays are being utilized in different fields for the general operation of switching. These are switching devices that are operated and controlled by a small signal in a system. The product lineup of the relays is as follows:

General Purpose Relays

• The general purpose relays are used for the different kinds of general switching operations. Different kinds of relays with different operations fall in the category of general-purpose relays. The general purpose relays include the power relay, ratchet relay, latching relay, and other relays as well which are used in different systems. General-purpose relays are also available for the control panels. 

Terminal Relays

• The terminal relays are used in different panels to save some space. The installation of the different equipment in a control panel for the purpose of terminals is a complex job. To avoid the multiple components and to save some space in panels terminal relays are used which provide the terminals for the basic connections. Different manufacturers provide different kinds and types of terminal relays.

I/O Relays

• I/O relays are used for the connection purpose of the PLC with other components and controllers. The terminals of the I/O relay are used for connection purposes. The I/O relays are used in different systems to get rid of the complex wirings. These relays are simply used for the connection of the different inputs and the outputs without using wiring for the same connection. Terminals are available in this kind of relay for the connection of inputs and outputs.

Solid State Relays

• Solid-state relays are the popular kind of relays that are provided by a number of manufacturers and are used commonly in different applications. In a solid state relay semiconductor is utilized for the operation. High frequency and high-speed operation are provided from the solid state relays. The solid-state relay is also called the no-contact relay.

The different terms for the relay are divided into two categories. One category is the general relay term and the other category is the contact section. The different terms associated with the relays are defined in the following sections.

General Relay Terms:

The general terms for the relay are as under:

Coil Designation

• The designation of the coil is represented with different symbols as per the state of the coil. The latching relays will have their own symbol for the reset condition and normal condition. Similarly, other relays will have their own coil designation symbol.

Nominal Coil Voltage

• The voltage value flowing in the normal operation of the relay is termed the nominal operating current for the relay.

Nominal Operating Current

• The current value flowing in the normal operation of the relay is termed the nominal operating current for the relay.

Nominal Operating Power

• The nominal value of the power consumed by a relay in normal operation is termed the nominal operating power of the relay/

Coil resistance

• The resistance of the coil is observed in the DC relays. The resistance of the coil in dc type relay is termed coil resistance. 

Pick up Voltage

• The values of the voltage at which the contacts of the relay are in operating condition are termed the pickup voltages. 

Drop out Voltage

• The value of the voltage for which the operating for which the operation of the relay is reverted to a non-operating condition is called the dropout voltage. The dropout voltage for different relays is different. 

Maximum applied Voltage

• The maximum amount of voltage that can be continuously provided to the coil of the relay without any damage caused to the coil is termed the maximum applied voltage. 

Contact Section

The terms for the contact section of a relay are:

Contact Forms

• The contact form is used to represent the mechanism used for the contacts of the relay and the number of contacts used in the relay.

MBB Contacts

• The contacts of the make-before-break relays are called the MBB contacts. In this type of contact one Form is open and the other is closed respectively. 

Rated Switching Power

• Each relay type has its own rated switching power which is set by the manufacturers. The switching operation is performed at a certain value of the contacts of the relay and this is termed the rated switching power.

Maximum Switching Voltage

• The maximum switching voltage value which can be handled by the contacts of the relay is called the maximum switching voltage. 

Maximum Switching Current

• The maximum switching current value which can be handled by the contacts of the relay is called the maximum switching current. 

Maximum Switching Power

• The maximum power at which the contacts of the relay can operate is termed the maximum switching power. The power across the contacts should not be exceeded above this value in order to keep the relay in its working state.

Maximum Switching Capacity

• The maximum switching capacity of the relay is predefined by the manufacturer. It is the value that is obtained from the maximum switching current and the maximum switching voltage.

Contact Resistance

• The resistance measured across the contacts when the contacts are in contact with each other is termed as contact resistance.