Lessons · Industrial control · one coil, one rung
One coil, one rung
If either condition should drive the output, that is a branch. If both must, that is series. Either way it is one rung.
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
It makes the program mean what it says, and it makes the next person's cross-reference honest.
How to think about it
Merge, do not delete blindly: both conditions were put there by somebody who wanted them. Work out whether they are an OR or an AND, write the one rung, and remove the dead one so nobody edits it expecting an effect.
Worked example
{ [A] | [B] } (Lamp)Either one lights it. A on, B off. Lamp: 1[A] [B] (Lamp)Both required. A on, B off. Lamp: 0
Your turn
Either condition should light the lamp. Join them.
{ [A] [B] } (Lamp)Run a rung and watch the scan
The trap
Leaving the dead rung in place because 'it works now' hands the next person a rung that cannot do anything and looks like it can.