How Ladder Logic Program Scan Works

PLC programs scan cyclically. This means that it is repeated many times and in the same order. The primary sequence of a PLC scan is reading the inputs, executing the program, diagnostics, and communication, and updating the outputs. We will look at these scan items with particular attention to how the ladder logic program is … Read more

PLC Learning Series – Program Cyclic Scan

Programmable logic controllers (PLC) use a cyclic scan. The time that it takes to complete one scan is called Scan Time. Typical scan times range from 10 milliseconds to 10 microseconds. This translates from 0.01 to 0.0001 seconds per PLC scan. Understanding how the program scan will help us in programming and troubleshooting the PLC. … Read more

PLC Fiddle Shift Register Challenge

Shift registers will move (shift) bits in a word (register) to the left or right. If we look at an example of boxes moving along a conveyor belt, the boxes would represent the bits in the register. The movement of the conveyor would be the shifting of the register that represents the movement of the … Read more

PLC Fiddle Compare Instruction Challenge

Just about every program usually has some data comparison instruction. This is the ability to compare information from one area of the controller to another and act on results. The output of this comparison conditions the logical continuity of a rung. PLC Fiddle is a free online browser simulator and has the following compare contact … Read more

PLC Fiddle Math Challenge Examples

PLC programming will often involve math equations that need to be solved. Every manufacturer of programmable logic controllers will include math logic for you to use in your programs. Numbering systems play an important role. You can usually perform math using BCD (Binary Coded Decimal), Binary or Floating Point. Here is a link that will … Read more

PLC Fiddle Counter Challenge – Counters

Counters are used in a lot of PLC programs that I have seen. A timing chart is a secret behind understanding the counter that you need in your application. Making a timing chart before writing the program will ensure that all of the information will be accounted. The secret to using counters is a good … Read more