need help

[bernie_carlton]

I wonder if this will be one of those exercises with 'now that you have the simplest example modify it assuming momentary switches' type situations with increasing complexity after each round. I can think of lots of stuff.

 

[JRB]

I whooped this up just for the fun of it, seems like it might work given limited details.

 

[bernie_carlton]

JRB, in your example, assume that switch 1 was pressed then, later, switch 2 was pressed. The alarm is sounding. Switch 1 is then reset. Switch 2 immediately controls the alarm and it continues uninterrupted. This is the same action as there being no intermediate NC contacts in the ladder.

The only difference would be if switch 3 had been the initial switch made. Upon it being reset the alarm would be off for one scan time. A negligible difference.

 

[Bering C Sparky]

In that example if more than one switch were pushed (and maintained) at the same time then there would be NO alarm sounding until one of the switches were opened back up.

You would be better off with only one rung and just have the 3 inputs in parallel to a single OTE.

 

[bernie_carlton]

You are looking at his ladder wrong. The intermediate NC contacts are not inputs, they are the contacts from the individual coils at the ends of the rungs.

But, as I noted, there is no net advantage over the simple parallel rung version.

 

[Bering C Sparky]

You are looking at his ladder wrong. The intermediate NC contacts are not inputs, they are the contacts from the individual coils at the ends of the rungs.

But, as I noted, there is no net advantage over the simple parallel rung version.

You are correct, I did look at that wrong. (Damn Dyslexia)
Trying to do 5 things at once and still get in some PLCS.net time.

My bad!!

BCS

 

[JRB]

JRB, in your example, assume that switch 1 was pressed then, later, switch 2 was pressed. The alarm is sounding. Switch 1 is then reset. Switch 2 immediately controls the alarm and it continues uninterrupted. This is the same action as there being no intermediate NC contacts in the ladder.

The only difference would be if switch 3 had been the initial switch made. Upon it being reset the alarm would be off for one scan time. A negligible difference.

"the only switch capable of turning off the alarm, if activated, is the switch that set the alarm".

Three parallel contacts do not meet the above criteria, (where only the switch that set the alarm can turn it off).

The last switch to turn off is not the same as "the switch that set the alarm".

And, even if we assume as you did that switch 2 was pressed and maintained after pressing switch 1;

The alarm is sounding because of switch 1.
And only switch 1 can turn the alarm off. (meeting the criteria of the OP)
If switch 2 is pressed after switch 1,
Then switch 2 immediately becomes the switch that set the alarm, once switch 1 turns the alarm off.
And only switch 2 can turn the alarm off. (again meeting the criteria of the OP)

Now in your haste to unwhoop my simple circuit, do you agree that it perfectly meets the criteria the OP
asked for, and 3 parallel contacts don't?


Why don't you all provide your own examples, instead of misinterpreting mine?

 

[pal]

JRB - I'm sorry I can't totally agree although technically your arguement is sound from a programmers point of view .
From the OP's 1st post , a member of management comes down to check . Switch 1 starts the alarm . Switch 2 is then turned on . Switch 1 is turned off but the alarm still sounds and in this case the alarm does not go off even for 1 scan . The alarm does not stop till switch 2 is turned off . The management would not accept this as complying with their request .
Unfortunately , I'm at home & don't have Logix 500 so I hope you will accept apologies and a description for a possible solution . To your logic in #17 I'll add 3 sets of 3 rungs before the alarm output . I'll only describe the 1st of each set for alarm 1, since the other two are repeats of the 1st with different addressing to suit alarms 2 and 3 .

Change the alarm switches to latched in the rungs 1 to 3 .

Set 1 - New rung #4 E_SW2 NO in parallel with E_SW3 NO . Then in series ALARMSW1 NO and latched output ON_2_OR_3

Set 2 - New rung #7 E_SW1 NO in series with E_SW2 NC and E_SW3 NC. Then Unlatch output ON_2_OR_3

Set 3 - New rung #10 ON_2_OR_3 NC in series with E_SW1 NC . Then Unlatch output ALARMSW1

All switches are off . When E_SW1 is turned on , ALARMSW1 latches on and as per your last rung ( now rung #13 ), the alarm sounds .

If E_SW2 is turned on then ON_2_OR_3 is latched on . ALARMSW1 can't be turned off until ON_2_OR_3 is unlatched .

ON_2_OR_3 is only unlatched when E_SW1 is on AND E_SW2 & E_SW3 are both off

Paul

 

[Bering C Sparky]

Why don't you all provide your own examples, instead of misinterpreting mine?

@JRB
First off let me apologize to you for not seeing your post correctly and making coments that had nothing to do with what you actually had posted.
I did not do this intentionally and meant no ill will toward you in doing it.
I have been quick to jump the gun lately and trying to do more than one thing at a time, and I have been making lots of mistakes because of it.
This is something I need to work on and improve.
Again...Very Sorry.

Yes. To accomplish what they ask is trickier than the straight forward parallel rung we have all probably envisaged by now.

Why trickier though?...

@Geospark
Once again you have proven yourself to be the GURU high atop the mountain.
This was not as easy or straight forward as first perceived, and this is what you were trying to point out in the beginning of this thread.
In fact it might be easier to use Non-Maintained Switches to Accomplish this than to use Maintained.

Even though we are not supposed to post homework logic, I would love to see how others might handle the same problem.

Anyway I gave it a go and it is posted below.
I had to post each of the 3 rungs as a separate JPEG and I also included the zipped .rss file.
This logic should qualify what has been requested although it may be a bit unorthodox.
(This is based on using 3 Maintained Switches, so it follows suit with what has been discussed previously)

BCS

 

[willxfmr]

This actually looks like the kind of work orders I get. No real information, just a vague concept that offers more questions than answers.

Will.

 

[JRB]

Hi Paul;

I really can't concur, because any time any alarm switch is on, the single alarm in this simple system should
be on, right? If SW2 is pressed after SW1, there must still be an emergency, so why would you want the alarm to
turn off if SW1 is pulled out, and SW2 is pressed in, even for one scan? What purpose would any blurp in transition
serve? My example only meets the criteria set forth in the original post, it may not survive repeated assault from
conjured up images and possibilities not expressly stated in the original post.

My circuit, albeit half-assed, was just something I whooped up in minutes to help jlchandler on his way, but I have
this funny feeling he checked out right after posts 2&3. Sometimes, these test type questions seem very easy for
anyone not trying to figure them out, and it's also easy to see how a beginner may have trouble even starting to.
That's why, rather than berating the poster, if I can help, I always try to offer some solution in visual form,
even if other posters attack it like a hunk of bait fish in the most frightening episode of Shark Week(TM). If it
can provide a starting point, that's a chance I'm willing to take.

Bearing C, no offense taken, no need to apologise, no animosity towards anyone. I'm not a programmer, I'd like
to see how others might do it too.