What is Seal-in Circuit ?
A Seal-in circuit is a method of maintaining current flow after a momentary switch has been pressed and released. What is Seal-in Circuit ? Fig 1 : Start button not…
What is Interposing Relay in a PLC System ?
Interposing Relay is the auxiliary relay which is used to isolate the two different systems / devices. This could be because they have different 0V references, different voltages, AC vs. DC. Interposing…
PLC Valve Control Ladder Logic Programming
Objective : To understand the basic concept of PLC Valve Control Ladder Logic. Target Users : Students, Technicians, Freshers, Trainee engineers. Note : Barrier or Relay not shown in above…
PLC Analog Input Scaling
An Allen-Bradley SLC500 programmable logic controller (PLC) uses a 16-bit analog-to-digital converter ( in its model 1746-NI4 ) in analog input card to convert 4-20 mA signals into digital number…
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…
