OMRON provides General-purpose Relays, I/O
Relays, Power Relays, Latching Relays, and Ratchet Relays.
Overview of General-purpose Relays
What Are Relays?
To get an idea of what relays are, think of a children's athletic
Little A holds on tightly to the baton and passes it to the Big B.
This is a relay.
Now lets look at a more technical example.
Think of turning on a television with a remote control.
Structure and Principle of Relays
A relay consists of an electromagnet that receives an electric signal and
converts it to a mechanical action and a switch that open and closes the
Schematic Diagram Showing the Principle of Relays
Principle of Operation
In this example, we will turn ON a lamp using switch S1 and a relay.
1. Press S1 to turn it ON.
2. Current i flows to the operating coil and
magnetizes the core.
3. The armature is drawn to the core by the
4. When the armature reaches the core, the
moving and fixed contacts make contact and the lamp lights.
5. When S1 is released to turn it OFF,
current no longer flows to the operating coil, the electromagnetic force
no longer exists, and the armature returns to its original position by the
force of the release spring.
6. When the armature has returned to its
original state, the contacts become separated and the lamp turns OFF.
Applications for Relays
Relays are used in most machines and devices
that use electricity.
Types of Relays
There are different ways to classify relays. The following groupings will
be used in this technical guide.
Types of Electromagnets
Relays are classified into the following types, depending on whether or
not they have a permanent magnet.
Non-polarized relays do not use a permanent magnet in their
This means that generally the operating coils do not have polarity.
There are some non-polarized relays, such as those with built-in operation
indicators, or surge-absorbing diodes, whose operating coils have
Polarized relays use the magnetic flux of the permanent magnet in their
electromagnetic sections. This means that the operating coil has polarity.
Description of Relay Operation
Single-side Stable Relays
No current is applied to the operating coil, so the electromagnet does not
operate. The armature is pulled by the force of the release spring in the
counterclockwise direction and, as a result, the moving contact makes
contact with the normally closed contact (turns ON) and the normally open
contact stays disconnected from the moving contact (remains OFF).
When current flows to the operating coil the electromagnet is magnetized
and the armature is drawn to the core. As a result, the moving contact
moves away from (turns OFF) the normally closed (NC) contact and connects
(turns ON) the normally open (NO) contact.
Latching Relays (also called 'Bistable' or 'Keep' Relays)
Magnetic Latching Relays: Two-coil Latching Relays
Relaxed State (after Reset)
The diagram shows the relay in the relaxed state.
Latching relays are the same as the single-side stable relays described
previously except that the core, yoke, and armature aremade from semi-hard
magnetic material and there are at least two coils in the relay.
Operating State (Set)
When current flows through coil A, the electromagnet (made of semihard
material) is magnetized and the armature is attracted to the core.
As a result, the moving contact moves away from the normally closed (NC)
contact (turns OFF) and makes contact (turns ON) with the normally open
In the set state, the residual magnetic flux in the semi-hard magnetic
material (material that has properties similar to a permanent magnet) will
keep the armature attracted to the core even if a current is no longer
applied to coil A.
Release State (Reset) To Relaxed State
If a current is applied to coil B, which is wound in the opposite
direction to coil A, the residual magnetic flux in the semi-hard magnetic
material will reduce and the magnetic attraction will weaken. The power of
the release spring will become stronger than the magnetic attraction, so
the armature will release and the relay will be in a relaxed state.
When the armature has released, there will be almost no residual magnetic
flux in the semi-hard magnetic material.
Note: In contrast to the hard magnetic material used in a permanent magnet,
semi-hard magnetic material requires less energy to magnetize and
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