Sorta OT: Relay Contact Race Condition

Hello Guys,

I've been reading through some training material on sequential relay-controlled pneumatic systems. I've come across a circuit design method used by a large equipment manufacturer and something has been bothering me about their method that maybe some of you guys who worked on old school relay systems can shed some light on.

Take a look at the excerpt of the wiring diagram attached. Look at nodes 29-32. Relays K14 & K15 designate states, and K10 & K7 are conditions for entering those states, respectively. They use this method to guarantee that the states are followed in a specific order.

Now here's my problem. If K14 is active and transitioning to K15, when K15 goes on, if the NC contact of K15 opened before the NO contact of K15 closed, then K15 would never be latched on. The NO contact of K14 would open up, so K15 would switch off, and the machine would not be in either of these states.

Would this be a reasonable concern if one were to build this system? I posted recently about an E-Stop circuit design similar to this that had timing issues and the contacts bounced back and forth infinitely, that experience brought me on to this thinking.

Thanks!

While there is some concern, from the time of application of power to K15 its NC contact would have to open, K14's coil would de energise, then its contact, which was closed, would have to open. In that same time the NO contact of K15 would have to close. The closing of K15 would probably win (one event versus 3) but it would be best to research timing diagrams (opening and closing) for the relays. It wouldn't be appropriate in a safety type circuit.

Hi Bernie,

Thanks for the tip regarding the timing diagrams. After doing some research, I guess this would be a typical application for control relays with make-before-break contacts?

Thanks!