Lessons · Industrial control · where the stop belongs
Where the stop belongs
In series with the whole rung, outside the branch -- so it breaks every path, not just one of them.
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
Inside the branch, there is a way around it, and the way around it is the start button somebody is already pressing.
How to think about it
A branch is a set of paths to the coil. Trace each one separately and ask whether it crosses the stop. If any path does not, that path can hold the output up on its own.
Worked example
{ [Start] | [Motor] [/Stop] } (Motor)The stop moved onto the seal leg only. Start pressed on scan 2, Stop held from scan 3, Start still held on scan 4. Motor: 0 1 1 1 -- it never stops.Your turn
Where does the stop contact go?
in with the whole rung
Run a rung and watch the scan
The trap
With Start released this broken rung behaves perfectly. It needs both buttons at once to fail -- which is precisely what a frightened operator does.
Practise where the stop belongs on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.