Weird Micrologix 1000

Hey guys, I saw something really weird on 3 different brand new Micrologix 1000 1761-L32BWA. After downloading the program and put on run mode, output 10 was on. I checked the program and that output is never used in the program, also the forces were not installed nor enabled. I measured the voltage in the output and it was 120 VAC, even more weird is that if I force the output off, the voltage goes away. So a bad relay is not an issue, I think. Has anyone seen anything like this? Thanks for your comments.

I can't remember if the Micrologix 1000 indicates by a fault if it has no program. If so, was this indication present? I'm thinking possibly a test program which was not erased. Does your program use output 10? If so does it work correctly?

bernie_carlton said:

I can't remember if the Micrologix 1000 indicates by a fault if it has no program.

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I loaded the program, its and old program that I have and that is used in other identical machines.

bernie_carlton said:

If so, was this indication present? I'm thinking possibly a test program which was not erased. Does your program use output 10? If so does it work correctly?

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The indicator for output 10 was on, and the actual output had voltage, my first thougth was a bad relay, but if I force the output off, the voltage goes away. The output 10 is not used in the program. The progran works ok because there is no need for that particular output.

Definitely a weird one, but there is always a reason. Maybe the program is turning it on at the word level? If something writes 1024 to word O:0.0, output 10 will turn on. Also, is there an HMI connected? That could be turning on the output as well.



-Eric

Eric Nelson said:

Definitely a weird one, but there is always a reason. Maybe the program is turning it on at the word level? If something writes 1024 to word O:0.0, output 10 will turn on. Also, is there an HMI connected? That could be turning on the output as well.



-Eric

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There is nothing writing to a word, only individual outputs going on, and there is no HMI.

What you are describing is consistent with a "1" simply being placed in the data table at the Bit 10 position.

If that bit isn't referenced in the program, it will simply turn on. You could force it off, or just put a "0" in the data table.

What I've never heard of is a zero being in the data table and the output indicator being on.

While this might be an old program, it's certainly possible that somebody opened it and inadvertently placed a bit in this data table location.

I have seen this exactly as Ken described it. Someone put a bit in the bit box ( as Ron likes to say) or that address was used at one time then changed while a one was still there. Just toggle it off.

Don't forget to change the offline file.

Ken Roach said:

What you are describing is consistent with a "1" simply being placed in the data table at the Bit 10 position.

If that bit isn't referenced in the program, it will simply turn on. You could force it off, or just put a "0" in the data table.

What I've never heard of is a zero being in the data table and the output indicator being on.

While this might be an old program, it's certainly possible that somebody opened it and inadvertently placed a bit in this data table location.

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Probably that is what happened.