Lessons · Industrial control · what a broken wire does
What a broken wire does
Wired and written correctly, a break stops the machine. Wired normally open and written [/Stop], the same break leaves it running with a dead stop button.
Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.
What it is for
One of those two failures is a production problem. The other is the one that hurts somebody.
How to think about it
Compare the two directly. The input sits at 0 either way; what differs is whether the rung reads 0 as 'stop' or as 'nothing is wrong'.
Worked example
{ [Start] | [Motor] } [Stop] (Motor)Correct. Running, then the wire breaks on scan 4. Motor: 0 1 1 0 0{ [Start] | [Motor] } [/Stop] (Motor)Wired normally open instead. The same break. Motor: 0 1 1 1 1Your turn
A protection nobody exercises is a protection nobody knows they have
Run a rung and watch the scan
The trap
The second version passes every test anybody runs, because everybody tests by pressing the button, not by cutting the wire.