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Publication 700-AT001A-EN-E June 2002
Chapter
1
Basic Concepts of SSRs
Overview
What are SSRs?
Difference between SSRs and Mechanical Relays
SSRs (solid-state relays) have no movable contacts. SSRs are not very different in
general operation from mechanical relays that have movable contacts. SSRs,
however, employ semiconductor switching elements, such as thyristors, triacs,
diodes, and transistors. Furthermore, SSRs employ optical semiconductors called
photocouplers to isolate input (control) and output (load) signals. Photocouplers
change electric signals into optical signals and transmit the signals through space,
thus fully isolating the input and output sections while transferring the signals at
high speed.
SSRs consist of electronic parts with no mechanical contacts. Therefore,
SSRs have a variety of features that mechanical relays do not
incorporate. The greatest feature of SSRs is that SSRs do not use
switching contacts that will physically wear out.
SSRs are ideal for a wide range of applications due to the following
performance characteristics:
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