What is a Seal Circuit and How Does it Work (Programming Ladder Logic For PLC Mechatronics Part 2)

Welcome to intro to mechatronics part 2. In this video we will be going over seal circuits in ladder logic.
For your reference I have a summary of the last video on this slide.
So to start off lets take a look at a 2 normally open contact inputs, and one normally off coil
The first input contact will represent a start button this is designated with a letter A. This button when pressed will connect the circuit
The second contact which we will refer to as B is a stop button and this is wired so it is normally closed or in other words is always connected until the button is pressed then the circuit is no longer connected.
These 2 contacts are connect to a coil that will represent a motor with a fan
Now lets take a look at what happens when we press the start motor button A. The motor starts running. Notice that the stop motor is powered on by default. We will be representing a closed contact by a yellow box around the contact and the flow of electricity by a yellow arrow.
So now lets see what happens when we stop press the start button… The motor turns off. Notice that this logic makes it so you will have to continuously press the start button for the motor to stay on. You could circumnavigate this problem by having a start toggle switch. Or we could use a seal circuit
So what is a seal circuit. It is a circuit that remembers that the start button was pushed. We add another coil that is x1 which is a memory bit to remember that the switch was pressed and we put that same bit in parallel with the start button or in other words or gated so that if either the start button is pushed or it remembers that the start button was pushed the motor will run. We then place another rung that has a contact of x1 that when activated completes the circuit and power the motor which is coil x2.
Now lets see what happens when we press the start button power flows through the a and b contact to the x1 remember coil. On the next rung the x1 contact is energized which energizes the x2 run motor coil
Now if we stop pressing the start button the energy now will flow through the x1 remember branch and power the motor.
To break the seal circuit we can turn on stop button which is a normally connected button to break the circuit. Now the remember bit is off and the motor is off.
When we release the stop button the motor stays off.

Disclaimer
These videos are intended for educational purposes only (students trying to pass a class) If you design or build something based off of these videos you do so at your own risk. I am not a professional engineer and this should not be considered engineering advice. Consult an engineer if you feel you may put someone at risk.

[michelakpro]

excellent video, simple and clear thanks

[VAM_Physics_and_Engineering]

I noticed i received a dislike... the probable reason is due to the normally open contact for B. to be clear there is a difference between wiring a normally closed button and programing a normally closed contact. If we were to place a normally closed contact at b then the wired button would counter act it and it would be a normal button. This might be a topic for a future video.