What is Ladder Logic Diagram?
Ladder Logic is a programming language is to programs a Programmable Logic Controller. Ladder Logic is used to develop a program for a PLC.
Ladder Logic Diagram also known as Ladder Diagram (LD) is the most common programming language used to program PLCs. It is a graphical language that shows a logical relationship between inputs and outputs as like they are relays.
Single Push Button START/STOP Ladder Logic Diagram
Siemens TIA Portal v15.1 software is used to program Siemens PLCs. In this post, we have used S7-1500 series PLC which has 16 digital inputs, 16 digital outputs, 5 analog inputs, and 2 analog outputs.
For programming single push button ON/OFF function, we require only one input. One output is used to show the result on the PLC trainer. In real-time, if you are not needed to use any output, one can use a Memory tag instead.
Below is the list of PLC tags used along with their address.
I0.0 – Push Button ON/OFF (Input)
Q0.0 – Desired Output (Output)
M0.0 – ON Memory (Memory)
M0.1 – OFF Memory (Memory)
The Push Button used in this example is normally open (N.O.).
Single Push Button ON/OFF Ladder Logic Program uses only 3 rungs to give an output. To explain the program, it is divided into 3 networks. Network 1 explains the logic when we press Push Button for the first time i.e. to start the cycle. Network 2 explains the logic when we again press the Push Button to stop the cycle. And network 3 explains Single Push Button ON/OFF logic.
When Push Button is pressed, N.O. The Push Button gets closed to turn on the ON Memory M0.0. Please note that, as we are pressing the Push Button for the first time OFF Memory must be normally closed (N.C) in order to turn on M0.0.
And when the Push Button is pressed for the second time, M0.1 turns ON (explained in network 2). As M0.1 turns ON, N.C. M0.1 in network 1 turns OFF cutting the power of M0.0 and thus, M0.0 turns OFF.
On pressing the Push Button for the first time, M0.0 which is N.C in network 2 will turn N.O., Q0.0 will turn N.C. and M0.1 will not turn ON.
For the next push button press, M0.0 will turn N.C and M0.1 will turn ON. As M0.1 turns on it will cut off the power supply of the output Q0.0 explained in network 3 and the system turns OFF.
After pressing the push button, M0.0 turns ON as explained in network 1. In network 3, M0.1 is N.C. and hence M0.0 ON condition turns ON the Output Q0.0. Note, that, this output must be latched in order to keep the system running.
|Single Push Button ON/OFF Ladder Logic Diagram|
|Single Push Button START/STOP Ladder Logic Diagram|