Relay: Structure of Relays and Operating Principles. 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. Relays are used in the different circuits for the different purposes from which the switching purpose is the main concern.
There are different categories of the relays depending upon the structure and the operation of the relay. However a general relay structure of a relay comprise of the following parts.
The electromagnets used in the relays are made up with the help of coil. The coil wire is wrapped on a core of soft iron. The soft iron core is used for the path for magnetic flux. As the name suggest 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 the connection purposes or the contact purposes.
- Switch Point Contacts.
The switch point contacts in a relay are used for the 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.
The above mentioned components in a structure of 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 the relays are being utilized in different fields for the general operation of switching. These are switching devices which are operated and controlled by a small signal in a system. The product lineup of the relays is as follow:
- General Purpose Relays:
The general purpose relays are used for the different kind of general switching operations. Different kinds of relays with different operations fall in the category of the general purpose relays. The general purpose relays include the power relays, ratchet relays, latching relays 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 the terminal relays are used which provide the terminals for the basic connections. Different manufacturers provide different kind and types of the 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 the connection purpose. 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 these kind of relays for the connection of inputs and outputs.
- Solid State Relays:
Solid state relays are the popular kind of relays which 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. A high frequency and high speed operation is provided from the solid state relays. The solid state relays are also called the no-contact relays.
Relay – Explanation of Terms:
The different terms for the relays 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 the 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 as the nominal operating current for the relay.
- Nominal Operating Current:
The current value flowing in the normal operation of the relay is termed as 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 as 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 as the coil resistance.
- Pick up Voltage:
The values of the voltage at which the contacts of the relay are in the operating condition are termed as the pick up voltages.
- Drop out Voltage:
The value of the voltage for which the operating for which the operation of the relay is reverted to non-operating condition is called the drop out voltage. The drop out voltage for different relays is different.
- Maximum applied Voltage:
The maximum amount of voltage which can be continuously provided to the coil of the relay without any damaged caused to the coil is termed as the maximum applied voltage.
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 the certain value of the contacts of the relay and this is termed as 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 as 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 which 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 the contact resistance.
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