This fourth edition of Programmable Logic Controllers continues to provide an
up-to-date introduction to all aspects of PLC programming, installation, and
maintaining procedures. No previous knowledge of PLC systems or programming
is assumed. As one reviewer of this edition put it "I honestly believe that
someone with little or no background to PLC systems could take this book and
teach themselves PLCs"

What is a PLC (Programmable Logic Controller)?

A Programmable Logic Controller, or PLC, is more or less a tiny computer
with a built-in operating system (OS).

This OS is highly specialized to handle incoming events in real time, i.e.
at the time of their occurrence. The PLC has input lines where sensors are
connected to notify upon events (e.g. temperature above/below a certain level,
liquid level reached, etc.), and it has output lines to signal any reaction
to the incoming events (e.g. start an engine, open/close a valve, etc.)
The system is user programmable. It uses a language called "Relay Ladder"
or RLL (Relay Ladder Logic). The name of this language implies the fact that
the control logic of the earlier days, which was built from relays, is being
simulated. The PLCs purpose in life

The PLC is primarily used to control machinery. A program is written for
the PLC which turns on and off outputs based on input conditions and the
internal program. In this aspect, a PLC is similar to a computer. However,
a PLC is designed to be programmed once, and run repeatedly as needed.
In fact, a crafty programmer could use a PLC to control not only simple
devices such as a garage door opener, but their whole house, including
turning lights on and off at certain times, monitoring a custom built
security system, etc.

Most commonly, a PLC is found inside of a machine in an industrial
environment. A PLC can run an automatic machine for years with little
human intervention. They are designed to withstand most harsh environments
a PLC will encoun.

Download File Size:77.61 MB

---