two buttons

[FONT=&quot]Working on a class lab - gots some ideas but how to make it work in sequence has got me befuddled..
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[FONT=&quot]Two push buttons have to be pushed in the right order to operate a door. The order is 1 and then 2. If the right sequence is not pushed, an alarm is to go off and keep the door from operating until a reset button is pushed.[/FONT][FONT=&quot][/FONT]

Hi BB, l will get in first and ask you to show what you have already programmed/written, to enable people to offer help/guidance, as most on the site will realise it is most probable a example/exam question, that you don't seem to have put much effort in answering.

hi BB

please provide some more details in regards with ORDER ?? & RIGHT SEQUENCE ??
What kind of order do you want ? what is the right sequence of operation ??

Regards.
Meghnesh

Hi Broad Bruce,

There has to be more to the application. You at least need some kind of time factor involved. Otherwise, somebody could happen to press the first button one day & somebody else press the second button a week later. I've done a skeleton of the application in vBuilder Flow Chart programming. The same thing can be done in ladder.

This example was sized to fit on a single screen shot. You probably need to add logic to determine that the buttons return to inactive, but this is the basic logic. If someone doesn't do a ladder example, I will try to do so later today.

Their are to many unknown variables, what kind of PLC you are using, what programming language you are trying to achieve this in ladder, structured text, SFC, function blocks? etc...

broad bruce said:

[FONT=&quot]Working on a class lab - gots some ideas but how to make it work in sequence has got me befuddled..
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[FONT=&quot]
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[FONT=&quot]Two push buttons have to be pushed in the right order to operate a door. The order is 1 and then 2. If the right sequence is not pushed, an alarm is to go off and keep the door from operating until a reset button is pushed.[/FONT]

Click to expand...

Given the simplistic nature of the assignment, this must be a beginning level class. So first off, if we (collectively) do your work for you, what have YOU learned? You've learned how to manipulate others into doing your work for you!
Congratulations, you have just switched your track to Business Management...

So to offer more constructive guidance (aside from the overly complex solution already posted), break this down into basic logical elements. Button #1 (I01), Button #2 (I02), Reset Button (I03), Door Motor Controller (Q01) and Alarm (Q02).

Then start making ladder logic or boolean logic statements for the sequence you described. For example:

If
I01
And
I02
Then...

Hint: you may need one or more Marker Relays (M) in your logic.

You need about 3 rungs. I will show you one way to do the first 2 rungs. The last rung is for the Door Output. Rung 2 should have the following addresses: Stop Pushbutton, Door UP Limit Switch, Alarm Output, One Before Two flag relay, Pushbutton 2, and the Door Output.

looks like another student who lance does the exam for.

No, only part of this lab problem (not a exam). Most likly he had to turn it in uncompleted with only the 2 rungs. For most students, the working ladder logic is so foreign and so far removed from what they know, so that what they really need are working examples, not a bunch of lectures about how it works.

Learning how it works comes later with hands-on experience for most of us.

Hi Lance, I'm just taking the "mickey",all the people that you have helped I'm sure appreciate it. I also like your well explained logic and they way you emphasise the importance of giving descriptions on how the rungs work, as l and all others have come across unexplained logic and have to waste precious time in trouble shooting, working out the reason for the code. I am certainly no PLC specialist but l enjoy the different approaches all the people who post answers, enable me (as long as my memory remembers) to write better code. Has everyone notice how BB posted the question 2 days ago, didn't answer any posted questions then has received an answer to his problem and not a thanks to people for helping him?