Simple question...need a simple answer

EmesiS

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Join Date
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New Mexico
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I'm using a MicroLogix 1000 and I want to use the same output in different sections of my logix. Basically a timer triggers that output on and off then it goes to the next process. Then later on in the logix it needs to be triggered again in a repeat process. But because it is the same output it is not coming on. I can change it to a different output in the logix and the ladder works fine. I'm using different bits to trigger the output, but the output is cancelled out in the logix. There should be a way to do it without using subroutines or sequencers but I just can't seem to figure it out. So does anyone have any suggestions...thanx.
 
EmesiS said:
I'm using a MicroLogix 1000 and I want to use the same output in different sections of my logix. Basically a timer triggers that output on and off then it goes to the next process. Then later on in the logix it needs to be triggered again in a repeat process. But because it is the same output it is not coming on. I can change it to a different output in the logix and the ladder works fine. I'm using different bits to trigger the output, but the output is cancelled out in the logix. There should be a way to do it without using subroutines or sequencers but I just can't seem to figure it out. So does anyone have any suggestions...thanx.
Click to expand...

are you saying the output is being set in different locations throughout the program, or seperate bits are being ORed in one location only?

Ian
 
You can use the contact --| |-- for the output in as many places as you want in a program. You should only use the coil --( ) once. If you use it more than once only the logic from the rung closest to the end will execute properly because the ladder scans top to bottom.
 
Yes I want to use the same output in different parts of the program. And using different bits to trigger it. Hope you understand...thanx.
 
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Basically Either Bit will turn on the output. Those two XIC instructions, lets call them B3:0/0 and B3:0/1 (paralleled) will be set elsewhere in your logic by the two conditions you want to turn the output on, Lets call the output O:0/0.

If either B3:0/0 or B3:0/1 is true, then O:0/0 turns on.

Edited to make it easier to understand. And fix a few typos
 
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Ok so say I need to turn that same output on and off in 3 different placed in the program, would the parallel bits work. I know all this can be done using sequencers but I am just a rookie and still learning.

Also this is a great forum, I'm impressed with the quick response time and people here are truly helpful. Thanks for all the input.
 
Yes, you can use 3 seperate paralled bits to turn on the output, and turn on the bits in 3 seperate locations.

This is the correct way to drive a single output from multiple locations. OTEs should never be used more than once per Input/Output/Bit.

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EmesiS said:
Ok so say I need to turn that same output on and off in 3 different placed in the program, would the parallel bits work.
Click to expand...

Yes, the parallel bits would work.

EmesiS said:
I know all this can be done using sequencers but I am just a rookie and still learning.
Click to expand...

Have you read the learn PLC's section on this site, would be a great place to start to understand the basics of PLC operation.

There is also the simulator which gives grahical examples of different processes, very educational I think.
 
One way is to select a binary word, say B3:0 (make sure no bit of the word is used anywhere) then set B3:0/0 to on where required, also set B3:0/1 where required. Then on a rung have a compare block "if B3:0 is not equal to zero" then set the real world output to on.
Hope this makes sense.
Regards Alan Case
 
One way is to select a binary word, say B3:0 (make sure no bit of the word is used anywhere) then set B3:0/0 to on where required, also set B3:0/1 where required. Then on a rung have a compare block "if B3:0 is not equal to zero" then set the real world output to on. Hope this makes sense. Regards Alan Case
Click to expand...

That works (pretty much the exact same way too), but I still think having the seperate bits in XICs, paralleled, is better, because you can clearly see which bit is on, and have a nice description visible right up front. It makes troubleshotting so much easier.

I have a large machine at work that uses what you suggested for Faults and Alarms. And stops the machine if the Alarm word is not equal to zero. It annoys me so much cause I can't see which fault happened right off hand, I gotta go look deeper.
 
You can still see which bit is on via the binary representation of the word in the NEQ block and it keeps the code for the real output on 1 page even with 16 separate bits being set.
Regards Alan Case
 
Tharon.

In RS500 if you use a compare instruction on a word from a "B" file type you should be able to see the bits displayed. This doesn't work the same when comparing a word from the "N" file type.

B_file_comp.JPG


BD

EDIT: Note to self, must type faster!!!!
 
I didn't say you _couldn't_ see the bits, just that you could _clearly_ see the bits and their descriptions with an XIC for each bit.

In my opinion at least, it's just much faster to find out what's happening when I can see each seperately. I also keep the quick cross refrencing under the instructions on, makes for easy navigation through programs.

So much easier to see "B3:0/1" with a description "Request from Step 5 - Move Conveyor Forward" and "B3:0/2" "Request from Step 7 - Move Conveyor Forward".

Edit: We have 2 programmers (My Boss, Myself, pretty new, out of college, been working 8 months) and a 3rd electrician who knows very little about PLCs. We try to keep everything very followable and well described, to make it easier for people who didn't program the machine to be able to troubleshoot it while the programmer is busy or on vacation.
 
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