Outputs will not fire

I am using studio 5000 for the program. For some reason even when the ladder logic is completely true to fire the output, the output still will not fire even in the program. Any suggestions on anything that would cause that?

Are the outputs in a subroutine? If so is that subroutine being called?

Is the plc in run mode or remote run?

Yes they are in a subroutine, The subroutine is being called, the plcs in remote run.

Are the outputs used anywhere else in the program?

No they are not.

Let's start with something real basic.....

Right-click on the output and select Toggle Bit. If the bit turns on/off each time you toggle it then the logic is not executing. Don't force, just toggle.

OG

I tried to toggle the output bit. It doesn't do anything. We executed the logic so the whole rung was "true" only leaving the output to fire. It still does nothing.

I made a separate test rung in the same subroutine with just a bit that I could toggle and an output bit. That output will turn on.

One thing I do when writing a program and emulating or commissioning it is create a DINT tag for Ladder_Is_Running and in the beginning of the main routine MOV 0 to it.

Then in each subroutine OTE Ladder_Is_Running.1 for the first, .2 second and so on.

Then in rung before the above MOV 0 I put a line of XIC L_I_R.1, XIC L_I_R.2, and on until the last used bit ending with a NOP.

When online if a rung is being scanned and turns on its bit then that XIC will show true. If one never shows true then the call is not there or if conditional not being called.

When troubleshooting an existing program to see if a subroutine is being scanned I do the same with only a single bit.

Ok, that confirms the logic is executing. Now, right-click on the output and select Cross Reference.

That should opne a windows at the bottom with a list of all locations where that output bit is being used. Look at the column labeled "Destructive" and under that look for all occurences with a "Y". That would indicate any locations where that bit is being turned on or off.

One of those will be the rung you ar eworking on. If there is more than one, then that is the problem. If two rungs are trying to affect the same output at the same time the last one in the scan cycle wins and the first one won't appear to operate correctly (as you have described).

OG

corbett11 said:

I tried to toggle the output bit. It doesn't do anything. We executed the logic so the whole rung was "true" only leaving the output to fire. It still does nothing.

Click to expand...

I would right click on the output and Find All to see if it is being cleared elsewhere.

There may also be a command clearing the entire output card, or doing a masked MOV to clear certain bits.

Another thing to check is add a branch around the output and create a OTE Test_Bit and see if the Test_Bit comes on. If it does the rung is being scanned true but somewhere else the output is being turned off.

One other thing you can try is trending the OTE tag. In the sample rate window set it to 2-3ms and watch the trend when the rung is true. You may see a blip every now and there where the scan rate and trend sample hit just right and turns on then off again within a couple milliseconds.

If this happens it is likely as others have said. Cross reference to make sure the OTE isn't used ANYwhere else. Even if the tag is being used as an OTE in a rung that you have blocked or added an AFI to it will still cause issues.

This is because when the program scans your rung that is true your tag will be set to 1. Then the scan continues and to the other rung that is false, sees the same tag as an OTE and then sets the tag to 0.

This has hit me a couple of times when I'm redesigning a station and reusing/changing outputs. I block the old rungs so I can keep track of the original program in case I need to revert back. Then I remember I have to fully delete the old OTE.

Another basic check, make sure you have 24VDC or 120VAC coming out of the output card. Maybe a blown fuse down the line?

What is the specific output module?

All this interest in the output module........It isn't turning on in the logic.



OG

Operaghost said:

All this interest in the output module........It isn't turning on in the logic.



OG

Click to expand...

Just curious what it is. Some modules can be taken out of run mode or disabled and won't turn on in the logic.