Brochure

ESG
8.458.45
8.458.45
8.45
General
Definition
A SSR (solid state relay) is able to perform many tasks
that an EMR (electromechanical relay) can perform. The
SSR differs in that it has no moving mechanical parts
within it. It is essentially an electronic device that relies
on the electrical, magnetic and optical properties of
semiconductors, and electrical components to achieve
its Isolation and relay switching function.
Over the last ten years many standards have been set
regarding SSR packages, most notably the rectangular
package which has now become an industry standard for
power switching using SSRs, with models ranging from 1
to 125 A.
Applications
Since its introduction the SSR, as a technology, has
gained acceotance in many areas, which had previously
been the sole domain of the EMR or the Contactor. The
major growth areas have come from Industrial Process
Control applications, particularly heat/cool temperature
control, motors, lamps, solenoids, valves, transformers.
The following are typical examples of SSR applications:
manufacturing equipment, food equipment, security
systems, industrial lighting, fire and security systems,
dispensing machines, production equipment, on-board
power control, traffic control, instrumentation systems,
vending machines, test systems, office machines,
medical equipment, display lighting, elevator control,
metrology equipment, entertainment lighting.
The Advantages of the Solid State Relay
When utilised in the correct manner for the intended
application, the SSR provides many of the characteristics
that are often elusive in the EMR; a high degree of
reliability, long service life, significantly reduced electro-
magnetic interference, fast response and high vibration
resistance are significant benefits from SSRs.
In today's environment we have all come demande,
rather than to expect, improved performance from the
components that we use. The SSR offers Designers,
Engineers and Maintenance Engineers significant
advantages over alternative technologioes, further
enhanced by the use of Surface Mount Solid State
circuitry.
These advantages are namely consistency of operation
and longer usable liftime. The SSR has no moving parts
to wear out or arcing contacts to deteriorate, which are
often the primary cause of failure within an EMR. The
long term reliability of components used within SSRs
has become well established throughout industry, and
with no moving parts to become fractured, detached, or
to resonate during operation, makes the SSR solution
more robust when used in unfriendly environments.
• Zero voltage turn-on, low EMI/RFI
• Random turn-on, proportional control
• Long life (reliability) > 10
9
operations
• No contacts - handles high inrush current loads
• No acoustical noise
• High switching frequency
• Microprocessor compatible
• Design flexibility
• Fast response
• No moving parts
• No contact bounce
In terms of internal design, the SSR and the EMR are
fundamentally similar in that each has an input electri-
cally isolated from the output that control a load. Fig. 1
shows the basic configurations of both the SSR and
EMR. In the case of the SSR, the isolation is achieved by
photocoupling and transformer coupling, and in the
Application notes (SSR)
EMR by means of a magnetic coupling.
Comparing the two technologies, the input control of the
SSR is functionally equivalent to the EMR, while the
output device of the SSR performs the switching func-
tion of the EMR contacts.
The operating speed of the EMR is dependent upon the
time it takes for its mechanical mass to react to the
application and removal of a magnetic field. Operating
speed of the SSR is primarly determined by the swit-
ching speed of the output device, typically much faster -
microseconds for DC SSRs compared to milliseconds for
EMRs. In most ac SSRs, response time is related to
20 mW
LED
Optical
coupling
Photo detector
Current
Limiter
Snubber
Trigger
Output
device
(SSR)
AC solid state relay (SSR)
200 mW
Magnetic
coupling
Electro magnetic relay (EMR)
Mechanical
contacts
Armature
Iron
core
Coil
Fig. 1 Solid state relay and electromagnetic configurations