Electromagnetic Relays -
NO - Normally Open - when the relay is not energized or activated, this
terminal is open-circuit.
NC - Normally Closed - when the relay is not energized or activated,
this terminal is closed circuit.
COM - The Common Center Terminal in relays. This is the center terminal
that closes circuit with NC-NO.
The terminals are potential free and floating and are insulated from
the control signals or coil windings by many kilo volts. Many provide
visible isolation. These terms apply to SSR or Big Contacters too.
Solid State Relays -
They are called SSR as there are made of semiconductors and have no
moving parts to wear out. They do generate heat depending on load and
switching. Thyristors are used in most as they are rugged, mosfets and
IGBT may also be used for various applications.
In this section you will find SSR designs and PCB layouts which you can
study. These were made and sold by me years ago. So the PCB
layouts have gone thru some revisions and they worked quite well.
Applications -
Many machines and equipment use some SSRs in their products which may
need replacement. So the SSR is not only sold to OEMs but also to
Service-Maintenance Market. These are also modified as Output
Modules for digital outputs coming from embedded systems or Computers.
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