A programmable logic controller (PLC) or programmable controller is an industrial computer that has been durable and adapted to control production processes such as assembly lines, machines, robotic devices or any activity that requires high reliability, easy programming and diagnosis of process errors. Dick Morley is considered the father of the PLC, as he invented the first PLC, the Modicum 084, for General Motors in 1968.

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A programmable logic controller (PLC) or
programmable controller is an industrial
computer that has been durable and adapted to
control production processes such as assembly
lines, machines, robotic devices or any activity
that requires high reliability, easy programming
and diagnosis of process errors. Dick Morley is
considered the father of the PLC, as he invented
the first PLC, the Modicum 084, for General
Motors in 1968.

2. PLC scada system
• PLCs can range from small modular devices with dozens of inputs and
outputs (I/O), in an integral housing with the processor, too large a
modular rack-mounted device with thousands of I/Os that are often
interfaced with other PLC and SCADA systems. They can be designed
for many digital and analog I/O layouts, extended temperature
ranges, electrical noise immunity, and vibration immunity and
impacts.

3. Controlling machine
• Programs for controlling machine operation are usually stored in
battery-backed or non-volatile memory. PLCs were first developed in
the automotive industry to provide flexible, robust and easily
programmable controllers to replace hard-wired relay logic systems.
Since then, they have been widely accepted as highly reliable
automation controllers suitable for harsh environments.

4. Loop controller
• A PLC is an example of a hard real-time system because output results
must be produced in response to input conditions within a limited
time, otherwise unintended operation. PLCs originated in the late
1960s in the US automotive industry and were designed as a
replacement for relay logic systems. Previously, control logic for
manufacturing consisted mainly of relays, cam timers, drum
sequencers, and dedicated closed-loop controllers.

5. Hard wiring
• It was difficult for designers to change the automation process due to
hard wiring. Changes would require new involvement and careful
updating of the documentation. If even one wire was out of place, or
one relay failed, the entire system would fail. Technicians often spent
hours troubleshooting by examining schematics and comparing them
to existing wiring.

6. Relay system
• When general purpose computers became available, they were soon
used for control logic in industrial processes. These early computers
were unreliable and required specialized programmers and strict
control of operating conditions such as temperature, cleanliness, and
power quality. PLCs provided several advantages over earlier
automation systems. It tolerated industrial environments better than
computers and was more reliable, more compact and required less
maintenance than relay systems.

7. Programming language
• It was easily expandable with additional I/O modules, while relay
systems required complicated hardware changes in case of
reconfiguration. This made it easier to repeat the design of the
manufacturing process. With a simple programming language focused
on logic and switching operations, it was more user-friendly than
computers using general-purpose programming languages.

8. Ladder logic
• This also allowed his traffic to be tracked. Early PLCs were
programmed in ladder logic that strongly resembled the schematic
diagram of relay logic. In 1968, GM Hydromantic (the automatic
transmission division of General Motors) issued a request for
proposals for an electronic replacement for hardwired relay systems
based on a white paper written by engineer Edward R. Clark. The
winning proposal came from Bedford Associates of Bedford,
Massachusetts.

9. Electronics devices
• One of the people who worked on this project was Dick Morley, who
is considered the "father" of PLC. The Modicum brand was sold in
1977 to Gould Electronics and later to Schneider Electric, the current
owner. Around the same time, Modicum created Modbus, the data
communication protocol used with its PLCs.

10. Electrical devices
• Modbus has since become the standard open protocol commonly
used to connect many industrial electrical devices. One of the first
084s produced is now on display at the Schneider Electric plant in
North Andover, Massachusetts. It was introduced to Modicum GM
when the unit was retired after nearly twenty years of continuous
service. Modicum used the 84 moniker at the end of its product line
until the 984 was introduced.