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Relay Basics

General Knowledge of Relays

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Types of Coils

Coils are classified according to the types of magnetic circuits and operational functions.

1. Magnetic circuit

Non-polarized: Operating coils do not have polarity
Polarized: Operating coils have polarity

2. Basic Function

Relay is classified into two basic functions: single-side stable relay and latching relay (also called "Keep" relay)

Single-Side Stable Relay

The contacts turn ON or OFF only when an input signal is received.

Single-Side Stable Relay
Latching (Keep) Relay

The contacts turn ON or OFF when an input signal is received but maintains its contact position during power interruptions.

 Latching (Keep) Relay
  • Select the optimal relay that meets your application and sequence requirements.

Types of Contacts

Contacts are classified according to the types of contact forms and contact reliabilities.

1. Contact Forms

There are three types of contact forms: Form A contacts, Form B contacts, and Form C contacts.

Form A contacts ("Make contacts")

This is normally open contact and closes when a voltage is applied to the coil.

Make contacts
Form B contacts ("Break contacts")

This is normally closed contact and opens when a voltage is applied to the coil.

Break contacts
Form C contacts ("Transfer contacts")

Combines the Form A and Form B contacts in a single relay and when a voltage is applied to the coil, Form C contact moves away from Form B contact and connects with Form A contact (for single-side stable relays).

Form C contacts (Transfer contacts)
2. Contact Reliability

Contact configurations are classified into three types according to the reliability level: Single contact, Twin contact and Cross-bar Twin contact.

Contact reliability

High

Single Contact Single Contact

One common terminal with only one point of contact

Twin Contact Twin Contact

One common terminal with two points of contact; increases contact reliability

Cross-Bar Twin Contact Cross-Bar Twin Contact

Moving and fixed contacts come together at a right angle reducing the area of its contact point and enabling stable contact resistance. Reduces occurrence of contact failure by entry of foreign matter.

Types of Terminals

The terminal configurations are classified as follows:

Types of Terminal Terminal configuration Typical Relay Model
Plug-in terminal
Plug-in terminal

Emphasis on maintenance,
Lineup of dedicated sockets

MY

MY

PC board terminal
PC board terminal

PC board (through hole) mount type

G5NB

G5NB

Screw terminal
Screw terminal

Emphasis on maintenance,
Screw terminal connection

G7Z

G7Z

Surface-mount terminal
Surface-mount terminal

PC board (surface-mount) automatic mount type

G6K(-F/G)

G6K(-F/G)

Quick connect terminal
Quick connect terminal

Emphasis on maintenance,
Tab terminal connection

G2R-T

G2R-T

Enclosures

The terminal configurations are classified as follows:

  • × : Penetration exist
  • ○ : No penetration
  • △ : Penetration may exist
Enclosures Characteristics
Atmosphere Conditions
Dust and dirt
Harmful gas
Typical Relay Models
Flux resistant type
(PCB relay)
This type of structure prevents solder flux penetration into the interior.
 
(Protects from large amounts of dirt and dust)
×
G2R

G2R

Palstic Sealed
(PCB Relay)
This type of structure prevents solder flux and cleaning solvent penetration.
 
G5Q

G5Q

Unsealed
(Plug-in Relay)
This type of structure places the relay inside a case to protect against foreign substances.
 
×
MY

MY

Plastic Sealed
(Plug-in relay)
This type of structure places the relay with resin case and cover to minimize corrosion effects.
 
G2A

G2A

Hermetically sealed
(Plug-in relay)
This type of structure places the relay in a corrosion resistant sealed case using metal or glass purged with inert gas (N2) to protect from corrosive gas penetration.
 
MYH

MYH