Werner, what are you saying? That both forward and reverse starters can be activated at the same time in the above ladder logic? I don't see how, given that I have TWO sets of interlocks to prevent this, on rungs o & 1, and 3 & 4. Even if these fail, the Reversing motor starter (if it is a NEMA-rated starter) will also have an interlock that prevents both from being activated.
On rung 5 you have a contact labeled S:4/9 "alternate slow"
Is the purpose of this to alternate the horn (1 sec on and one sec off?)
Never saw this - looks right handy - need to learn about it.
This brings up an interesting topic: How do you handle audible alarms? One time long ago (before PLCs were in wide use), I was working in a chemical plant control room. The shift operator was complaining about an alarm horn that was going off on a nuisance trip. A control damper limit switch was stuck, and the horn kept sounding. The operator would push the Alarm Acknowledge button, the horn would quit for 15 seconds, then it would take off again, about 100 decibels. Finally the operator shouted, "It's either me or that horn! Either I am leaving or that horn is!" Then he picked up a hammer and knocked the horn off the wall.
Since that event, I have been cautious in the use of horns. There are many events that must have an alarm horn. When I use a horn, I never allow it to go continuously, except in a catastrophic event. I alternate, 1 second on, 3 seconds off. This is much easier on the nerves, and more acceptable to every operator that I have talked with.
Also, I use 4 alarm levels, unless otherwise required by the customer:
(1) Not serious, but you need to know about it eventually. Alarm is blinking light only.
(2) There is a problem and some action is required. Alarm is intermittant horn and light for 3 minutes, or until acknowledged, then blinking light until problem is resolved.
(3) There is a serious problem, and action is required immediately. Alarm is fast intermittant horn and light for 10 minutes, or until acknowledged, then blinking light until problem is resolved.
(4) This plant will explode soon, and you should run! Alarm is continuous horn until it blows. This level is rarely used. I seen it at the Eastman Composition 4 explosives plant up in Northeast Tennessee.