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[AC/DC/PLC]

Hi. Can I have help with a question/exercise? I thought I was close but I cannot finish it off. It’s written ladder logic for a Mitsubishi FX PLC. I’ll try insert attachments of the question and were I am with it.

 

[lee1968nh]

Don't be lazy. Do the work yourself and do not ask others to do it for you...just by asking this, you're revealing your future...not a pretty one if you lean on others. Lean on yourself!

 

[ASF]

Welcome to the forum! Lee seems to be going a little hard on you IMO - you have shown your work to date, after all, you're not just asking someone to do it for you - but I think you'll still need to give a bit more detail to get the folks around here to help. Which part of the problem can you not solve? Which parts are working? What have you tried so far? The more effort you show, the more help you'll get.

 

[Steve Bailey]

Have you been able to send your program to a PLC to see what works and what doesn't?

Personally I don't see why you abandoned your initial attempt in favor of M3.

I would also use an M1 or a Y0 contact in the counter rung to prevent accumulating the count when the conveyor isn't running.

For clarity I would put the counter reset rung immediately following the counter rung. Someone troubleshooting the system should not have to search to find how the counter is reset.

 

[AC/DC/PLC]

Ok, so it’s just my second week and I cannot keep up with the pace set by the engineers in my class. They finished this exercise in class and I hadn’t started it. I made the mistake of skipping year 1 for year 2 in Automation (because I was good at a redundant ladder logic 15years ago when I was learning my electricians trade.) I cannot test it as I won’t be back in lab until Friday week. I reached out to my lecturer and he’s all about going at your own pace and not try keep up with the others. He told me I can finish it in lab in a fortnight. I just want to complete this exercise so I can learn it. I guess all I need to do is reset the pause button but I already have the pause button as an output. So it’s not that I’m not trying because I’m actually at a dead end and I think there’s something that I haven’t been taught that the others have. I understand how to reset counters but I don’t know how to reset the pause button.

 

[Steve Bailey]

but I don’t know how to reset the pause button

To me the term "Push Button" implies a momentary device. The spec goes so far as to call out the start push button as momentary, but even though it doesn't do the same for the stop push button or the reset push button is not a reason to assume they aren't also momentary devices.

You do understand the way the PLC operates don't you? In your initial approach, you press the reset button while the count is greater than or equal to 5. That action resets the counter, driving the count value to zero. So the next program scan the reset rung evaluates as false.

 

[Lare]

You don't need M3 latch for reset button.
You only need to think, if resetting is possible only when 5 parts are counted or also if less parts are counted.
(Your original smudged handwriting is key)

 

[AC/DC/PLC]

The stop button is on the top rung. I have the pause button as M2 on the second rung to pause the conveyor after it counts 5. Unless your saying M2 goes back to not being not true? M2 is energized after 5 counts simultaneously product high light comes on, I need to know how to de-energize M2, so I was thinking of branching out M2 under rst C1 but that’s the second time used as an output and that wouldn’t return it to NC even in theory. Honestly cannot get my head around it

 

[AC/DC/PLC]

Ok let me have another look

 

[Lare]

M2 (coil) is false if your counter C1 is less than 5.

 

[AC/DC/PLC]

So M3 - RST C1 then bottom rung end is complete? I sent it to my lecturer he said I wasn’t finished I thought he meant M2 had to be de-energized. But maybe he meant end rung and test in lab. He told me to cross out that line and try again, something to do with the proximity sensor. Sorry my brain is fried.

 

[AC/DC/PLC]

Not de energized but I meant not true

 

[Lare]

So M3 - RST C1 then bottom rung end is complete? I sent it to my lecturer he said I wasn’t finished I thought he meant M2 had to be de-energized. But maybe he meant end rung and test in lab. He told me to cross out that line and try again, something to do with the proximity sensor. Sorry my brain is fried.

Your code rung which you have overlined:

C1>=5 X4 RST C1 Would zero counter.

You M3 is also reseting counter, but M3 is false after counter is resetted. M3 is then true only one scan and not needed (it would still work anyways)



Remove your 2 last rungs and use your original C1>=5 X4 RST C1 rung innstead of them. It is simpler.

 

[AC/DC/PLC]

Ok thank you Lare. And thanks to the rest of ye, I’m off for the next two weeks and I’ll try learn it inside and out. I was told that I would be fine in class even if I never did ladder logic before. I couldn’t believe what we had to answer day 1 in class but I’ve learned so much these past 3 days I feel like it’s actually a great way to learn.

 

[Lare]

Ok thank you Lare. And thanks to the rest of ye, I’m off for the next two weeks and I’ll try learn it inside and out. I was told that I would be fine in class even if I never did ladder logic before. I couldn’t believe what we had to answer day 1 in class but I’ve learned so much these past 3 days I feel like it’s actually a great way to learn.

X3 (prox sensor) is counting also if conveyor isn't running.


It would be good to add conveyor running bit to series before counter block as Steve allready pointed.