1746-NO4I woes

I have 2 identical systems, 1 beside me and the other 1000 miles away on site. During commisioning the NO4I started playing up, it gave just 4 VDC output from the externally supplied 24 VDC. So I got them to take it out and check it. It then stopped working altogether. Now the PLC cannot even see the card and it faults the program.

So I sent another NO4I card up that I know works and although it gives 24 VDC, it still does not work. The PLC cannot detect it. I have tried it in the original slot 9, then slot 5 and then 4. The PLC still cannot detect the card. Aslo when both cards were switched to backplane supply, no power light was present, only when switched to external power with the external power connected does the light come on.

The PLC is now comming back for more testing. Does anyone have any ideas as to what could have happened? I cannot guarentee that it worked properly before commisioning, but I suspect it did. Could ther be something wrong with the backplane?

Thanks
Stu

Greetings Stu ...

the NO4I ... gave just 4 VDC output

Click to expand...

first of all, the VOLTAGE output doesn't really mean anything ... the "I" on the end means that this is a CURRENT card ... if you truly need a VOLTAGE output then you need a 1746-NO4V module instead ... for the CURRENT card, the best test is with a milliammeter - and look for something along the lines of 0 to 20 mA ...

from the externally supplied 24 VDC.

Click to expand...

if you're using an EXTERNAL power supply, you need to make sure that the DIP switch on the card is set properly ... BUT ... since it's the wrong card anyway ... or (no offense intended) you're testing it wrong - you need to nail down the VOLTS or CURRENT issue first ...

So I got them to take it out and check it. It then stopped working altogether. Now the PLC cannot even see the card and it faults the program.

Click to expand...

best guess from where I sit: they pulled it out - or put it in - with the chassis powered up ... that's NOT recommended for an SLC system ... bad things can happen when you hot-swap the cards ...

So I sent another NO4I card up ... The PLC cannot detect it. I have tried it in the original slot 9, then slot 5 and then 4. The PLC still cannot detect the card.

Click to expand...

are you sure that the "Read I/O Configuration" feature was used (offline) correctly? ... and then downloaded to the processor correctly? ... mistakes in the procedure could be the culprit ... most common mistake: reading the I/O Configuration to populate the I/O list - but then failing to download the resulting setup to the processor ...

Could there be something wrong with the backplane?

Click to expand...

anything is possible ... here's one "bad dream" situation that I know of ... the "controls guys" were in the process of installing the PLC gear in the enclosure - which was lying face up and open on a set of sawhorses ... the "cleanup crew" came in that evening and used an air hose to clean up the shop floor ... problems occurred when the modules where inserted in the chassis - due to the dust that had settled there ...



good luck with your project ... please let us know what you find ...

It is a current card as it is driving a 4-20 mA controller. It should give 24 VDC and vary the current according to the output of the card, hence why I mentioned that it was only giving 4 VDC accross the terminals. Channel 0 was giving 0 VDC. The switch was in the correct spot for the backplane and external power settings.

In read io config, the card dissappears from the slot list, never to reappear. I will let you know what I find, if anything.

Thanks
Stu

stuman said:

It is a current card as it is driving a 4-20 mA controller. It should give 24 VDC and vary the current according to the output of the card...

Click to expand...

That is absolutely, positively NOT a good assumption!! It ~may~ give 24VDC, but it rarely does -- In 20 years of doing this, I've NEVER seen a current analog output give 24VDC! Ron gave you the correct method of testing a current-output -- use a ammeter. That's the ONLY way...

And, as I was reading it, I came to the same diagnosis as Ron -- it was removed and inserted under power -- that's an absolute no-no with SLC.

Yes, there could be something wrong with the backplane. Or there could be something wrong with the module. Or there could be something wrong in the program... or the field wiring... If it was truly working absolutely properly, then it stopped working, something changed... what was it??