Lessons · Industrial control · when both directions are called at once
When both directions are called at once
Each rung requires the other direction to be absent, so calling both makes each one block the other and neither runs.
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
Refusing is the right answer. A motor commanded both ways at once is a fault upstream, not a decision to make.
How to think about it
Read the report 'it does nothing when I press both' as the interlock working, and say so. Time spent removing an interlock is time spent removing the thing protecting the gearbox.
Worked example
[Fwd] [/Rev] (M1) [Rev] [/Fwd] (M2)Forward alone, then both called. M1: 1 0
Your turn
Both directions called at once. How many motors run?
Run a rung and watch the scan
The trap
A program interlock is not enough on a reversing contactor. Contactors weld. The dangerous combination is also made impossible in the wiring.