Lessons · Industrial control · contacts in series are AND
Series is AND
Contacts in series on one rung must all be closed for power to reach the coil: series is AND.
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
Guard closed AND key on AND start pressed: safety and sequencing conditions stack up, and series is how the diagram says 'all of these'.
How to think about it
List every condition that must be true, then draw them left to right on one rung. Order does not change the logic, so put the safety conditions first where readers look.
Worked example
[GuardClosed] [KeyOn] [Start] (Motor)All three must be on: AND.
[GuardClosed] [/Fault] (Ready)Series with a normally closed contact: closed AND not faulted.
Your turn
Both A and B.
[A] (Out)
Run a rung and watch the scan
The trap
A long series rung is a long AND. One contact nobody expected to be off makes the whole rung false, and the diagram does not say which one.
Practise contacts in series are AND on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.