What is a Relay? How does a Relay works!

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What is a Relay? How does a Relay works!

A Relay is electromagnetic switch. It is used in application to turn on and off circuit by low power signal, or where several circuits must be controlled by one signal.

Main parts in a Relay: 

• Electromagnet,
• Movable armature,
• Switch  point contact,
• Spring.

Relay has two types of contact:

• Normally open contact (NO) – contact is open when relay is not energized
• Normally closed contact (NC) –  contact is closed when relay is not energized

There are four different types of relay:

• SPST – Single pole Single throw – This relay has two terminal which can be connected or disconnected.  SPSTs are perfect for on-off switching.
  
• SPDT – Single pole Double throw – SPDTs are relays where common terminal connects to either of two others, never connecting to both at the same time. SPDT switches should usually have five terminals (including two for coil).
  
• DPST – Double pole Single throw – DPSTs  This relays are equivalent to a pair of SPST switches or relays actuated by a single coil. DPST switch has six terminals (including two for coil).
  
• DPDT – Double pole Double throw –  These are equivalent to two SPDT switches or relays actuated by a single coil.  DPST switch has eight terminals (including two for coil).
  

Relays are used whenever is necessary high power or high voltage circuit with low power circuit, especially when galvanic isolation is desirable.
High voltage or High current devices can be controlled with small, low voltage wiring and pilot switches. Operators can be isolated from the high voltage circuit. Low power devices, such as microprocessor can drive relay to control electrical loads beyond their direct drive capability.

Now days  there is another type of relay, Solid State Relay. Solid State Relay uses power of semiconductor devices such as thyristors and transistors, to switch current up to hundred amperes.

Electromagnetic relays are still commonly used in applications today because they are simple cheap and most important provide complete physical isolation between control and load circuit. In applications where a circuit must be completely ON or OFF with minimal on state voltage drop or to avoid danger of injury or damage of leakage current, electromagnetic relay is a better choice.

#relay #What is a Relay #How does a Relay works

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Animation: Sasho Boshinoski
Hrvoje Čočić
Story: Hrvoje Čočić
Category: Education
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