Duplicate Destructive Bits in PLCs. The BEST Program Scan Lesson.
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- čas přidán 14. 06. 2024
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Just because you can, doesn't mean you should. One of the things I try to pass on is make sure it is easy to trouble shoot, point that you show at the end of the video. Thanks Tim
100%... No where in here did I say we should but we do accidentally do it.
Thank you for the great explanation. Coming from a computer programming background where nothing happens if the trigger to a command is false, I had a hard time dealing with multiple commands controlling an output. To me, if the input to a rung was false, I expected the output to be untouched, but as you mentioned in the video, if the input is false, the controller will explicitly write a zero to the output.
I'm glad it was helpful
Very good instructional video! These two concepts (sequence of events and being very careful about using duplicate destructive bits) can be tough to see and caught even by experienced programmers. Thanks for sharing.
Thanks, I debated on editing the initial video and erasing it but I walked us right into it and felt I needed to explain it.
I’m glad you didn’t because it’s like I tell my guys, you can’t eat an elephant in one bite, so you have to take little bits and go back to eat some of the bites that you miss. I also told them the other day that a program bug was nothing more than a bite of the elephant that got missed. Like you have said before, “programming doesn’t change” but the programmer may not of thought of every scenario to fully debug it.
Good saying, I'll remember that
Hard lesson learned by new engineers the hard way, the world over. Good vid!
Yes it is whipped me many times. And apparently I still don't learn because I recorded the whole series and didn't notice it 😂
Great realistic video about how to troubleshoot logic!
Glad it was helpful!
great ! Thank you sir
You are welcome
Hi Tim,
At the 4:45-4:50 mark, you mention how the PLC scan still evaluates input6. I’ve asked the same question during a very advanced Rockwell Training Class with a certified Rockwell instructor who said that it does not get evaluated in order to decrease program scan rate times.
Is there any sort of official documentation from Rockwell that you could link stating explicitly that the input6 still gets evaluated?
It evaluates it every time. Look at the text view of the ladder and you can see the exact order.
@@TimWilborneis there any documentation that explicitly states that it evaluates every instruction? The ascii text representation of the rung is just another representation of the same rung in ladder. If I had a link to documentation, I’d have something to physically show people when they doubt whether the instruction gets evaluated or if it skips along to writing to the OTE bit location.
Yes it is in many of the software and processor manuals. I'm not near a computer for the rest of the month so can't site a specific link
I would duplicate an output like that, i have seen this done many times by people who say it is fine and what it does is inserts a bug into your program.
I would not do this, i am correcting what i said below. I have seen this done many times and it works most of the time and then it doesn't. It introduces a bug. I just corrected a long standing problem in one of our programs due to another tech using a duplicate bit. I was warned about this in school to never do this!