Brochure/Catalogue

Relay modules – Overview
Historical background
The term ‘relay’ was originally used for a station where
stagecoaches were able to change their tired horses for fresh
ones. The term ‘relay’ was given a totally different meaning
by the English physicist Charles Wheatstone (1802–1875).
In Wheatstone’s times, departing trains were advised of by a
bell ringing at the next railway station up the line.
This was achieved by connecting a battery in the rst station
to a bell in the second. However, as the railway stations
were generally several kilometres apart the power arriving
at the second station was often insufcient to ring the bell.
Wheatstone invented a switchgear apparatus that was
installed at the second railway station. This continued to
function even with low power supply levels. The switchgear
apparatus switched a second electrical circuit that actuated
the bell. This was the birth of the electromagnetic relay.
How a relay functions
A relay is an electromagnetic switch comprising of two
galvanically isolated circuits. Firstly the control circuit and
secondly the open circuit with the normally open contact.
As soon as the control circuit is energised, the coil creates
a magnetic eld in the core/yoke and attracts the armature.
The actuator now actuates the switch at the output, the
normally open contact (make contact) closes and the
normally closed contact (break contact) opens. When the
control circuit is turned off, the magnetic eld diminishes
and the return spring returns the armature to its initial
position. The actuator moves the normally open (make
contact) back to its normal position, the normally open
contact opens, the normally closed contact (break contact)
closes.
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Relay modules – Overview
A relay therefore offers the option of switching high loads
with low power, such as battery voltages, and acting as a
switching amplier. Thanks to the galvanic isolation
between input and output, a relay is also suitable for
providing isolation in the event of potential differences
between the control and operating circuits. If a relay also has
several working contacts, it can also be used as a contact
multiplier.
From relay to relay module
There are two alternative methods that make a relay module
suitable for use in industrial applications: mounting onto
a PCB – in combination with the corresponding assembly
techniques and circuitry – or plugging onto a specially
designed relay socket.
Generally, the design and rating data determine if a relay
module is or is not suitable for a particular application.
For example, relay modules with plugged on relays are only
partly suitable for use in applications subjected to heavy
vibrations. In this case, relay modules with soldered relays
should be preferred. Low, compact designs such as those
provided by the RIDERSERIES are utilised in small consumer
units where the overall available height is limited. Conversely,
the compact design of the TERMSERIES helps to save space
in electrical cabinets.
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Technical appendix/Glossary
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