hello, new here as registered, please help with ladder diagram

hello, i am maggiesparky and have visited this forum many times and just love it. well i have a ladder diagram question and ask for your help to correctly diagram the following scenario:

a n.o. pb will activate 2 pushrods (separate devices). when the pb is pressed pushrod A extends and holds for twenty seconds before returning to home. after returning to home pushrod B extends and holds for twenty seconds. upon returning to home the counter resets and circuit returns to the off state.

the second scenario is a little easier but i still miss the timing aspects: same pb, same pushrods; press pb to extend pushrod A it retracts and there is a twenty second delay before pushrod B extends. after pushrod B retracts the timer restes to zero and circuit remains at rest state (off)

this is the best i understand the question, it is very similar to one that could appear on a test i take soon to become an electrician at the plant where i work.

the proper placement of timers the ton, toff, and res are where i fumble...

thank you loads...for i just might become what i have been wanting to do for near 20 years...and put an old education at devry to work.
thank you again and so very much.

the plc brand is allen bradley, model of controller is rslogix 500/slc-500 instruction set, thank you jtshaffer.

welcome to the forum. what brand of plc, which model of plc, etc. Please post your program that you have started on.

hello, i misread the last part of your request as to post into message...i am working it out on pen and paper just as i would in the test. i have no access to a scanner to post it immediately; can probably scan it tomorrow evening. thank you again for your reply. i get the control over the solenoids, actuating the rods but it is the placement of the timer, the delay, and the reset that throw me.

pardon...the pb is n.c. ...thank you

maggiesparky said:

hello, i misread the last part of your request as to post into message...i am working it out on pen and paper just as i would in the test. i have no access to a scanner to post it immediately

Click to expand...

You can also use ms paint to make your drawing. Then use the attach files button.

1st Case: .....upon returning to home the counter resets and circuit returns to the off state.

2nd Case: After pushrod B retracts, the timer resets to zero and circuit remains at rest state (off).

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The major difference between your description of Case 1 and 2 seems to be the Counter, and the Timer. You will need 1 or 2 timers for each case to determine the 20-second delay for each pushrod.

If you can use a Counter for Case 1, then you only need 1 timer for both pushrods. Use the Counter to recycle Timer 0 to time each pushrod. If Counter = 0, time Pushrod A. If Counter = 1, time Pushrod B.

If you only have timers available in Case 2, then use 2 timers to make it easier. Timer 1 finishes the 20-second cycle for Pushrod A, then triggers Timer 2, which finishes the 20-second cycle for Pushrod B.

Are the two scenarios are independent of each other?

And, what is the counter for? what do you want to count?

Plus, how detailed do you want the whole system? Number of inputs/outputs, valve types to be used for pushrods, etc? or just ignore all that and keep it simple?

And, what is the counter for? what do you want to count?

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What he needs to count are the Case 1 Pushrod cycles: Counter = 0, 20 seconds for Pushrod A, followed by Counter = 1, 20 seconds on the SAME timer for Pushrod B.

Then for Case 2, use no counters, but use 2 timers, Timer 1 started by Timer 0.

Did you get your Pushrods working, Maggiesparky? It seems that you will need 3 timers for Scenario 2. Does one of the 3 have to be an Off Delay (TOF) timer?

Thanks Lancie1, any idea about the valves which will be controlling the pushrods? I mean are they going to be spring returned or double solenoid? that will determine the retraction and detraction logic.

Let me know, if you need the ladder logic straight away.

Thanks all,

Thanks Lancie1, any idea about the valves which will be controlling the pushrods? I mean are they going to be spring returned or double solenoid?

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It is not a real problem, but instead a training exercise, so AssUMe that the valves are spring-return type with only 1 solenoid - energize to extend, de-energize to retract.

The way you typecast "assume" makes me think it's happened to you before

Case 2 is trickiest - without feedback that the pushrods have extended fully, how will the PLC know when to turn the output off ? A PLC is much, much faster than a pneumatic or hydraulic actuator !!

If it just going to be done based on time, then Case 2 is the same as Case 1, but with different timings at different places in the sequence.

In the real world, however, it is most common that driven devices provide some feedback... What would happen if one of the pushrods failed to extend fully ? This is the sort of question that every automation engineer should be asking...

The way you typecast "assume" makes me think it's happened to you before

Click to expand...

Yes, about 9,000 times and counting.