AdvancedTopic 73 of 101Signals, Control & Comms
PLC and industrial control
Programmable logic controllers automate machines with ladder logic.
In depth
PLCs are rugged industrial computers executing scan cycles (read inputs, run logic, write outputs). Programmed in IEC 61131-3 languages: ladder diagram, function block, structured text, sequential function chart. Used for machines, conveyors and process interlocks with safety variants.
Key points
- Scan time
- Digital and analog I/O modules
- Fieldbus connectivity
ExampleA bottling line sequence is coded in ladder logic with timers and counters.
What is PLC and industrial control?
Programmable logic controllers automate machines with ladder logic.
Why is it important to understand PLC and industrial control?
PLCs control machines and processes in factories, so they are the workhorse of industrial automation.
What is ladder logic?
A graphical programming language that resembles relay circuits, widely used to program PLCs for industrial logic.
What makes a PLC reliable?
It is built for industrial environments with rugged hardware, deterministic scan cycles and watchdog protection.
How is PLC and industrial control used in practice?
Typical applications include automating a conveyor with start, stop and interlock logic, controlling a packaging line with sensors and actuators and sequencing a pump and valve in a water plant.
What should I learn before PLC and industrial control?
Study "Feedforward and cascade control" first (topic 72 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of PLC and industrial control?
Scan time. Digital and analog I/O modules. Fieldbus connectivity.
Can you give an example of PLC and industrial control?
A bottling line sequence is coded in ladder logic with timers and counters.
What comes after PLC and industrial control?
The next topic is "SCADA and DCS", which builds directly on this one.
How difficult is PLC and industrial control?
It is classed as Advanced in Signals, Control & Comms (topic 73 of 101). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Signals, Control & Comms.