Understanding the basics of LD
LD is an easy-to-learn programing language for creating control programs in PLCs to automate or control machines in industries.
In Chapter 1, Introduction to Industrial Automation, it was mentioned that prior to the introduction of PLCs, there was automation but through the use of relays, timers, contactors, and so on. These were hardwired together to perform the required control or automation task. Relay logic circuits were used when designing such control and were also used for troubleshooting the system.
A relay logic circuit is an electrical circuit or drawing showing symbols of components, such as relays, switches, timers, and contactors, and their connections for the desired control or automation task. The circuit usually consists of two vertical lines (rails), one on the extreme left (supply voltage potential, live or positive) and the other on the right (zero potential, neutral or negative). One or several horizontal lines in a relay logic...