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Old February 2nd, 2018, 09:20 AM   #1
VSeaver
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Micrologix 1000 First Scan Bit

I am pretty sure this has been asked before, but I am unable to find it any where. I have a first scan bit I am using to home 2 steppers on power up. The bit never comes on when I go from program to run. I looked in "Processor Status" and under the "Main" tab it says "No" for S:1/15. I am unable to select "Yes" for this. It is greyed out. I am sure there is something I am missing here.

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Old February 2nd, 2018, 09:48 AM   #2
OkiePC
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You will never see that bit when monitoring. To prove that it is working use it to drive a counter and then switch modes a handful of times and see if your counter changes.
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Old February 2nd, 2018, 09:57 AM   #3
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I have a timer in the same rung as this bit, but it never starts timing. I put a dummy bit in parallel with the status bit and toggle it and the timer times.
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Old February 2nd, 2018, 10:32 AM   #4
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Quote:
Originally Posted by VSeaver View Post
I have a timer in the same rung as this bit, but it never starts timing. I put a dummy bit in parallel with the status bit and toggle it and the timer times.
And when you untoggle it the timer resets?
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Old February 2nd, 2018, 10:37 AM   #5
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Rather than using a timer or counter. Just put a latching rung around S:1/15.

S:1/15 M1
---| |-------------( )
M1 |
---| |------
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Old February 2nd, 2018, 11:03 AM   #6
VSeaver
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When I toggle off the dummy bit the timer does reset. The program is written. So when I do toggle the dummy bit, the steppers home and the program runs fine. It's just when I either cycle power or go from program to run, the first scan bit does not start the first part of my program which is to make sure everything is home before starting the reset of the program. I may be wrong here but I would assume it is something to do with enabling it in the processor status menu.
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Old February 2nd, 2018, 12:08 PM   #7
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Hi,

Normally use something as shown attached. Useful for masking certain alarms or other equipment on power-up. Set the .PRE as necessary.

Regards,

Rob
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File Type: jpg FirstScan.jpg (18.9 KB, 37 views)
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Old February 2nd, 2018, 12:08 PM   #8
Mickey
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Post the program if you can. It's .RSS file (zip it first)
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Old February 2nd, 2018, 12:17 PM   #9
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I am not in front of the PLC right now so I tried the Emulator and put in program and back to run and it worked this time. Not sure what is going on. I will have to try it with the actual PLC when I get to it. It is at another facility at this time. I have attached the program.
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File Type: zip Dadant CTL Ladder Logic.zip (25.0 KB, 9 views)
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