I don't understand!

[baldyspate 0]

Hi Fellas: This isn't critical and it's not going to be fixed or replaced. I'm curious though... An SLC500/? w/120V inputs and triac outs: The program on one rung uses an input and an output as a simple relay. -------| |----------------------------------------------------( )----- I:2/0 O:5/8 In this case, when a real input is applied the card shows such on the led display, but there is no output. Using a laptop I toggled the input and it showed active in rslogix while the output did not.(in rslogix or for real) When I toggled the output with rs... it showed active on the screen, the led, and energized the motor starter it is connected to. I understand a proc reads the inputs to a file, processes the values to an output file, and then writes the outputs to the ouput card. I'm having trouble picturing how the above combination of results could happen. Thanx for any answers or ideas.

[Guest trn_psycho]

Sounds like the output is being used elsewhere in the program. Right click the output and select find all. Make sure that there isn't some other logic keeping it from going high. It could also be that it's in a sub routine that isn't being called (JSR XX)

[Guest]

I'm betting (a LOT more than pocket change) that the Ladder File which contains that rung is not actually being SCANNED by the processor ... chances are you need a JSR instruction in Ladder File #2 to "send" the processor over to the "subroutine" file ... if this isn't your problem, post your RSS file and we'll help you figure it out ...

[baldyspate 0]

Sorry, I don't have access to the file and the net at the same time. Paranoid people. This is on the fourth rung of the first file in the program. There are 11 files, but not jups or calls, etc, ahead. There are only writes to bits and a timer ahead of this rung. It's the second input and first output of the program. I only discovered it because I was wondering why there were two wires to the ouput when there should have been only one. Someone had moved the input wire (from two p/p switches in series and supplied from the same power terminal as the output commons ) to the output terminal, maybe years ago, to apparently get around the problem. Leaving O:5/8 attached, natch. Seems a little....dangerous. I love this site...wish I stopped in more.

[baldyspate 0]

You made me rethink. Thanx both Psycho and Ron It's a rare thing, but I may be wrong.... about the previous rungs. There may be a mov or some such I can't check for a while but I'll bet one of you are right. either somethings interfereing or changing the initial value in said output file bit. thanx... If you're still interested I'll fill in some blanks tomorrow. in this toopic

[Guest]

ALWAYS interested ... that's what we're here for ... if you're sure that your mystery rung is located in the "first" ladder file (usually that's ladder file #2) then check for instructions like JMP or TND in the rungs above (before) the one that's giving you the problem ... best plan of attack: post your RSS file - if you can do it without getting in trouble ...

[baldyspate 0]

Oops... There was a jump statement and it was the culprit. The physcal input which would have made the (JMP) rung false had been removed along with whatever equipment it used to be wired to and undocumented wiring mods to go with it. I aggravated my troubleshooting problem by somehow latching the input true and leaving it that way for a while. I'm not real experienced with PLCs but even I should have noticed it. Thanx, it was fun and good experience, with RSLogix while correcting the problem.

[Guest]

thanks for coming back and "closing the loop" ...