Program specification number one from the previous section says:
“The Ball Mill, Cooling Fan, and a Lubricating Oil Pump should all go on when a start button is pressed.”
We could add the start pushbutton to each of the motor rungs, but there is a more efficient way to program this logic. We will use the start pushbutton signal to set a memory bit that indicates the motors should start.
Since we do not know how long the operator will hold in the start pushbutton, we add a branch around the start pushbutton signal to form a logic that is called a “seal-in”.
As demonstrated in other RealPars videos, "Why Should Stop Switches Normally Be Closed?" (https://bit.ly/3l6dxn5), the stop pushbutton is wired as normally closed in the field, breaking the circuit when the button is pressed. Therefore, we add an “Examine If Closed” instruction and add the stop pushbutton address to the bit.