Types of Relays

Different Types of Relays (Mechanical, SSR, Internal or External)
What are Relays?
Relays are the control switches that operate with low-powered
electrical signals controlling most types of circuits. An example
of an ideal relay application is having one electrical signal setup to control several circuits, allowing complete isolation of
electricity between the controller and the controlled circuits.
Think of these signals in relation to a “relay race” in sporting
events, where the race is made up of sequential parts,
and each team member passes from one to the next team
member, or with microwave or broadcast transmitter relays,
they repeat or reproduce transponder signals forward from
another source.
A relay acts as an insulator that protects the device being
used. When the control (input end), or the load (output end),
are not electrically connected, the relay prevents any power
surge damages to your application.
Using a system with large quantities of mechanical relays
makes it possible to safely switch multiple devices on and off
sequentially, in a particular order, or by using an automated
set of timers.
These relay applications above can help with understanding
different processes of relays using electromagnetic control
switches and operators, or solid state relay controllers.
Somewhere between 1831 and 1840, several inventors were
experiencing breakthroughs with their relay experiments and
perfecting their relay mechanisms for the electrical telegraph
intended to digitally amplify repeated signals for furthering the
range of previous telegraph transmission schemes. Basic Relay Designs
In some cases, multiple types of relays might be appropriate
for your specific application. Understanding the various
form factors, technologies, and styles of relays are essential
for picking the best-suited relay for your particular job
requirement. Some applications depend on certain strengths
of a relay application and many relays have limitations not
appropriate for all types of switches or controllers, V=IR.
Cybernetic Fountain
A common example of using multiple mechanical relays is
for controllers that trigger a Cybernetic Fountain display, timed
to coordinate with laser lights, water displays and music. An
example of one of these systems is Nam Van Lake Cybernetic
Fountain show, which features 288 spotlights and 86 spouts,
set-up as a precisely choreographed fountain show. Music
accompanies the show and a bit of laser action. Relays
associated with electrical circuitry include heating and air
conditioning controls, refrigeration, and washing machinery.
The input may be electrical with output directly mechanical or
the reverse set-up is often used.
Other types of relays include hydraulic or pneumatic relays. All
types of relays contain sensing units within an electric coil that
are on/off powered by AC or DC current.
Solid State Relays
Mechanical Relays These relays perform the same function but differ from
mechanical relays because they have no moving parts. Solid
state relays are semiconductor devices that use light rather
than magnetism to actuate switches. Most systems using
solid state relays, or SSR’s, have a light emitting diode or use
the light from a LED source. The load end of the open space
senses the light, triggering a solid state switch controlling the
opening and closing of the circuit.
The use of an electromagnetic coil that is energized by a
current to open or close a circuit for one or many mechanical
relays is a safe application because the system needs a power
source to operate. The magnetic field pulls or pushes the arm
of the switch, removing or initiating contact.
The advantage to using solid state relays is that they protect
circuits from electrical noise. SSR’s have no contact bounce,
they have low EMI/RFI, and compared to mechanical relays,
they have a longer life due to no moving parts. A solid state
relay can handle only single pole switching, however.
EZ Series
Intelligent Relay
http://www.omega.com/technical-learning / info@omega.com / 800.826.6342
© 2016 OMEGA Engineering, Inc. All rights reserved.
Introducing the New PlatinumTM Series Low-Cost
Temperature and Process Controllers
SSR330 and SSR660 Series
Solid state relays for Vdc and Vac input/Vac output
Pulsed output is a form of maintaining a contact position
indefinitely without any power needed to be applied to the
coil. Found in latching relays, stay, keep, or impulse relays,
the advantage to a pulsed output is that one coil will consume
power for just the instant when a relay is switched. This form of
pulse relay contact can retain an on/off setting across a power
outage. Using a remote control for building light systems
with pulsed output has none of the characteristic humming
produced when an AC energized coil is continuously on. For an example, two opposing coils fabricated with a
permanent magnet or an over-center spring holds the contacts
in position after the coil is de-energized. Using a pulse to one
coil switches the relay on, pulsing the opposite coil switches
the relay off. These relay forms are found in numerous industrial
applications such as in the Avionics industry, where controls
of simple switches and single-ended outputs are required
for high tech control systems. When relays require a remnant
core, to maintain contact in the operation position, a current
pulse of opposite polarity is required to release the contacts. The formula will be I=P/V. For example, let's assume we have
a 15,000 W heater, and that we are powering it up with 120V
to heat an aluminum sheet. The current will be 10,000/120=
80 A. As the example controller is using a DC pulse signal,
we will need relay SSRL660DC100, which is rated for 100 A. Example: SRFG-624/10-P + CN32PT-440 + SSRL240DC25. High-reliability, Vdc Input/Vac output, or Vac Input/Vac
output with thermal conductive pad, SSRL240 and SSRL660
series. Use the SSRL series for controlling large resistance
heaters together with temperature controllers. Three-phase
loads can be controlled with two or three SSR’s.
High accuracy with fast response, the Platinum series
temp controllers feature a three-color programmable display
capable of changing color and/or changing the state of
designated outputs every time an alarm is triggered. The
display is a large, 9-segment LED for various configurations
of mechanical relays, SSR’s, dc pulse, current outputs, or
analog voltage. CNPt Series
PLATINUM Series temperature
and process controllers
Analog output is fully scalable and can be configured as
either a proportional controller or as a retransmission to follow
your display. Includes universal inputs for thermocouple,
thermistors, RTD’s, and process voltage/current.
Why is this Product One of the Most Powerful Products
in Its Class?
OMEGA Engineering explains: “Additional features usually
found only on more expensive controllers make this the
most powerful product in its class. Some of these additional
standard features are: remote set-point for cascaded control
set-ups, high-high/low-low alarm functionality, external latch
reset, external ramp and soak program initiation, combination
heat/cool control mode, configuration save and transfer, and
configuration password protection.”
1. http://www.omega.com/pptst/SSRL240_660.html
2. http://www.omega.com/pptst/CNPT_Series.html
3. http://www.omega.com/subsection/scrs-ssrs-contactors-controllers.html
4. www.ni.com/white-paper/2774/en/
SRFR and SRFG Series Flexible silicone rubber fiberglass insulated
heaters. OMEGA flexible silicone heaters are lightweight and thin. Great
for operating temps of 56 to 232ºC. For gentle warming use 2.5 W/in2.
Rapid warming and high temperatures can be best achieved, controlled
at temp limits not to exceed the safe maximum of 232ºC, use 5 W/in2.
http://www.omega.com/technical-learning / info@omega.com / 800.826.6342
© 2016 OMEGA Engineering, Inc. All rights reserved.
Download PDF