Counting relay??

[brother]

I was chatting with a fellow electrician about fire door/curtain and it was interesting how it was wired. It has a 'safety edge' that when its comming down if it hits something it goes back up, and then starts to come down again. It does this 3 times, and after the 3rd time, it just closes wheather something is under it or not (so get out of the way!!).

Do they use something of a 'counting relay' for this set up?? Is there such a thing as a counting relay??

 

[iwire]

I would bet if the door is relatively new it has an electronic brain ruining standard relays.

 

[ohmhead]

Photo eye

Photo eye

Well how about a time delay relay or it can be done with many different devices or circuits like a electronic timer . I have seen your bump rail on a roll up door before but our door never had a delay if your under it a photo eye stops door from coming down if you out from under door it closes . best to ya

 

[iwire]

Here is a fire door controller with safety edge cycling, it is used in conjunction with a standard motorized door operator.

http://www.liftmaster.com/consumerweb/pages/productmodeldetail.aspx?modelId=875

Reading the manual it says it will try to shut the door three times and on the third time it hits an obstruction it will stop the door on the obstruction, not try to crush it.

Or with a change of dip switches it will drop the door by gravity after the third attempt.

LM21AFCB

Keep in mind there are thousands of fire doors that are closed by gravity and they will try to close regardless of obstructions once triggered.