LIM instruction problem - RSLogix5000

zitam

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• Apr 7, 2011

• #1

Hi,

I'm running a training and as an example I gave traffic lights using timer and LIM instructions.

Test value was Timer.acc and when students were using three LIMs in different rungs it doesn't work properly. LIM with limits of 0 and 25000 didn't turn up the light, next one (25000 to 30000) didn't work either. Only the last one with highest limits seems ok.

When we use only one limit instruction with LES and GRT instruction situation looks similar.

What may've caused the problem?

Matt

 

jstolaruk

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• Apr 7, 2011

• #2

You'll have to post the code. I use it all the time with no problems.

 

Steve Bailey

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• Apr 7, 2011

• #3

Did you use the same coil(s) in all three rungs?

 

zitam

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• Apr 7, 2011

• #4

lowest lim - coil for "green" light

middle lim - coil for "green" light and coil for "red" light in two branches

highest lim - coil for "red" light

 

MarkNightingale

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• Apr 7, 2011

• #5

Zitam,

That is why the lights are not coming on in the first 2 rungs of code. You should only have one output coil for each light.
When the code is being scanned because the final rung is not true it will be 'turning off' the output that has been turned on in the previous rungs.

Mark

 

Steve Bailey

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• Apr 7, 2011

• #6

Make the outputs of the LIM instructions three internal coils, "Low", "Middle", and "High". Then add two more rungs:

  Low         Green

--] [---+------( )-

        |

Middle  |

--] [---+

 

 High          Red

--] [---+------( )-

        |

Middle  |

--] [---+

 

MarkNightingale

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• Apr 7, 2011

• #7

Or just put both limit instructions in the same rung, which would make less tags and rungs of code.

 

MarkNightingale

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• Apr 7, 2011

• #8

Or just do this

 

Ron Beaufort

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• Apr 7, 2011

• #9

I'll bet your problems go deeper than that ...

I'm running a training

Click to expand...

the advice that my distinguished colleagues are offering you is excellent – but based on what you've posted, I've got a hunch that you would benefit by taking about 90 minutes of your time to watch the videos posted here:

http://www.ronbeaufort.com/sample_lessons.htm

be sure to watch ALL ELEVEN of them – IN NUMBER ORDER ...

IMPORTANT: when using RSLogix5000, there are some IMPORTANT DIFFERENCES in how the processors scan the ladder logic from what is shown in the RSLogix5 and RSLogix500 systems used in the sample lessons ... be sure to come back and ask questions after you watch the videos and we'll be happy to fill you in ... also - be sure to tell us whether you're using ControlLogix or CompactLogix systems for your classes ...

even with the scan differences, I believe your time will be well spent in watching these free lessons ...

 

Last edited: Apr 7, 2011

zitam

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• Apr 7, 2011

• #10

Sometimes I'm impressed by my stupidity

thanks for help

 

daba

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• Apr 8, 2011

• #11

zitam said:

Sometimes I'm impressed by my stupidity

Click to expand...

Like it !, and could probably think up hundreds of times I could have used it