SLC 5/03 Outputs Active During Program Anomoly

[Aabeck]

I have a SLC 5/03 setup I've been programming on the side to control Christmas lights, and just noticed an anomaly with this 5/03 - when I put it in Program mode to do a Sys Comms download (up to now I've done almost all programming using online edits) the outputs that are on at the time STAY ON when in program mode, throughout the download, & remain on until the unit is placed back in Run - then they respond like they should.

I went online with another 5/03 in a test rack & it shuts off all outputs as soon as it goes into Program, like I expected. I compared every setting between the 2 setups & the only setting different is "Index Across Data Files S:2/3" is No on the test rack & Yes on the Christmas lights system; and if I change bit S:2/3 on either to toggle the state it immediately toggles back to what it was. I even checked a 5/05 in another test rack & it says No & turns off all outputs in Program. It shows as a checkbox under Controller Properties, but can not be changed online, and I doubt this would cause the outputs to stay on in program mode. (EDIT: I just changed the Test 5/03 offline to Enable Indexing Across Data Files & downloaded it, it's now Yes & still turns off all outputs in Program mode.)

Both 5/03's are 1747-L552C, 32K, OS501 Ser C. Using RSLogix500 ver9.00 (CPR9). Zipped Xmas file attached.

Is there some other setting causing this or maybe a bad PLC? When I got more time (later) I'm thinking of swapping the 5/03's out & reprogramming them to see if it's in my program or in the 5/03 itself.

 

[Ron Beaufort]

when you say that the "outputs stayed on while in the program mode" - do you mean that the FIELD OUTPUTS (the actual devices) stayed on? ...

that would be truly weird ...

or ...

(1) do you mean that the OTE instructions on your RSLogix500 screen stayed "green on the screen" ? ...

or ...

(2) that the bit/boxes on your Output Image Table remained in a status of ONE ? ...

or ...

(3) something else ? ...

the next time you get a chance, see if the LEDs on the output modules stay lit up or not ...

note that you're using TRIAC type output modules ... if you're testing the ON/OFF condition of the output terminals - and you don't have a sufficient LOAD device connected, then it is NORMAL for the outputs to "stay on" - because they are passing a tiny amount of "leakage current" ...

you can search TRIAC here on the forum for more info - but the basic idea is that if you don't have a heavy enough load connected to a TRIAC type module, then the outputs will ALWAYS appear to be ON if you're using a sensitive meter to check the ON/OFF status ...

 

[Aabeck]

All of the LED's on the output card stay lit, and the corresponding TRIAC's are energized under load, with the field devices energized while in Program Mode. And when I first noticed this I had the last 2 output cards Relay Outs & they stayed on.

I wasn't looking at the status's in RSLogix, which do retain the last state when in Program Mode & show that online.

 

[Ron Beaufort]

I don't doubt that you saw what you're saying - but - that is definitely WEIRD behavior ...

personally I'm in the "let's learn something new" mode on this one ... it would be interesting to see if you can duplicate the same thing time after time ...

 

[Aabeck]

I've tried cycling power to it & re-downloaded my program & it still does it.

I just swapped out the two 5/03's & then reprogrammed both of them for the rack they are now in & the problem followed the 5/03 hardware - the test rack now has all the outputs staying on in Program Mode, the Christmas rack behaves properly.

I just pulled the Now-Test 5/03, removed the battery & shorted it to reset it to factory default, went to RSLinx to change the DF1 driver to the lowest speed you can imagine to talk to it & did a Sys Comm download, back to RSLinx to reconfigure the driver for 19,200, went online with the 5/03, put it in Run then back in Program & the output LED's & relay outputs on this rack stayed on!. And it doesn't matter if your change modes through RSLogix online or with the Program/Run key.

Definitely a hardware problem with the 5/03.

 

[Ron Beaufort]

I'd hang on to that one if I were you ... you should be able to find plenty of suckers who'd be willing to bet the rent that what you're seeing is totally impossible ... easy money ...

 

[Aabeck]

I was just wondering if this would be any value to any Rockwell engineers to determine this potentially deadly problem with one of their products?

 

[Ron Beaufort]

they might - or might not be - but personally I'd give you $50 for it to add to my lab equipment ... sounds like a very impressive little "show and tell" item ...

 

[Aabeck]

Just an update - while I was out this morning it popped up to me: "what would the outputs do if the PLC faulted?"

When I got home I added a DIV integer N7:10 by integer N7:11, set integer 11 to 1000, then added a SUB 1 from integer 11 - took about 1.2 seconds to fault the PLC with a Divide By Zero error - with all the outputs ON while faulted.

See attached picture to verify I'm not hallucinating. (The Battery LED is on 'cause I removed it)

 

[Doug-P]

with all the outputs ON while faulted.

Hence the admonition to E-stop outputs with hard relay contacts. Definitely adds some oomph to your 'potentially deadly' statement.

 

[Aabeck]

I just noticed something on my OP, I put the model of the 5/05 I had, not the 5/03's
The correct PLC # is: 1747-L532 Series D

Sorry.