Relays are electromechanical switches that are used to control circuits by opening or closing contacts in response to electrical signals. There are several types of relays, each designed for specific applications. Here are some common types of relays along with their symbols:

1. Electromagnetic Relay (EMR):
   • Symbol:
      
   • Description: EMRs use an electromagnet to mechanically operate the switch contacts.
2. Solid State Relay (SSR):
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   • Description: SSRs use semiconductor devices such as transistors to perform switching without any moving parts.
3. Thermal Relay:
   • Symbol:
      
   • Description: Thermal relays use the change in temperature to operate the contacts, protecting circuits from overloads.
4. Reed Relay:
   • Symbol:
      
   • Description: Reed relays use a reed switch enclosed in a coil to control the contacts. They offer high insulation and can switch high voltages.
5. Time Delay Relay:
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   • Description: Time delay relays operate after a preset time delay, used for applications requiring timed control.
6. Polarized Relay:
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   • Description: Polarized relays have a specific polarity requirement for operation, typically used in DC circuits.
7. Latching Relay:
   • Symbol:
      
   • Description: Latching relays maintain their state even after the control signal is removed until reset, making them suitable for energy-saving applications.

These symbols are standardized and widely used in circuit diagrams to represent various types of relays.