Mis-conceptions of PLC Ladder Logic
Perhaps the most important yet elusive concept to grasp when learning to program PLCs is the relationship between the electrical status of the PLC’s I/O points and the status of…
PLC Input Output Modules
Every programmable logic controller must have some means of receiving and interpreting signals from real-world sensors such as switches, and encoders, and also be able to effect control over real-world…
PLC Digital Input and Digital Output Modules
A “discrete” data point is one with only two states on and off. Process switches, push-button switches, limit switches, and proximity switches are all examples of discrete sensing devices. In…
Contacts and Coils in PLC Ladder Logic
The most elementary objects in Ladder Diagram programming are contacts and coils, intended to mimic the contacts and coils of electromechanical relays. Contacts and coils are discrete programming elements, dealing…
Motor Trip Logic using PLC Programming
Programmable Logic Controller (PLC) Questions and Answers This PLC is being used to start and stop an electric motor, and also to shut it down automatically if any of three…
PLC Program for Motor Starter
PLC tutorial explaining step by step procedure to program PLC for motor starter. Motor starters are of many types however the scope of this PLC tutorial is confined to simple…
PLC Pump Permissive Interlocks
The following PLC program was written to control the operation of a large electric motor-driven pump. A variety of “permissive” inputs protect the pump from damage under abnormal conditions, and…
What is Ladder Diagram Programming ?
Ladder Diagram (LD) Programming The most common language used to program PLCs is Ladder Diagram (LD), also known as Relay Ladder Logic (RLL). This is a graphical language showing the…
Basics of Fail-safe Circuits
Logic circuits, whether comprised of electromechanical relays or solid-state gates, can be built in many different ways to perform the same functions. There is usually no one "correct" way to…
History of Programmable Logic Controllers (PLC)
Every control system may be divided into three general sections: input devices (sensors), controllers, and output devices (actuators). The input devices sense what is happening in the process, the controller…
