Lessons · Industrial control · contacts in parallel are OR
Parallel is OR
Contacts in parallel branches give power two routes to the coil: either branch closed is enough. Parallel is OR.
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
Start from the panel OR from the remote, alarm on high temperature OR low pressure: alternatives are branches.
How to think about it
Write each alternative as its own branch inside braces, separated by |, then continue the rung with anything that must also be true. Series after a branch is AND after OR.
Worked example
{ [PanelStart] | [RemoteStart] } (Motor)Either start energises the coil: OR.{ [HighTemp] | [LowPressure] } [/Muted] (Alarm)OR inside the braces, then AND with not muted.Your turn
Either sensor trips the alarm.
{ [SensorA] [SensorB] } (Alarm)Run a rung and watch the scan
The trap
Two rungs each writing the same coil is not OR: the lower rung's answer wins. OR lives inside one rung, as a branch.
Practise contacts in parallel are OR on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.