AB Micro850 analog output card issue

Hello,

As you may remember, I posted in January about an issue we were having with our micro850 controllers (2080-LC50-48AWB) to operate irrigation booms in our nursery. Previous thread link - http://www.plctalk.net/qanda/showthread.php?t=127884

I was in touch with Rockwell, and they had 2 ideas:

• Swap the slots of the plugins to see if that helped.
• Try suppressors on the outputs

The issue we're facing is very random, so it's difficult to tell if the change you made helped, or if it wouldn't have been an issue during that time frame. So I swapped the plugin slots for a couple cards, and had no issues, but the device wasn't causing issues for a few days before the swap either... I swapped the cards back, and still no trouble...

Rockwell's second thought is to try suppressors for the outputs (we are using all but 2 of the 16 outputs. We're very tight on space in the panel - do any of you have ideas of what suppressor to try? It looks like Rockwell's supressors are a little too bulky to fit in the space we have. We're using 24vac solenoids on the outputs.

Also - random is very difficult to troubleshoot. When you have 65 devices, and any one of them randomly malfunctions once every couple weeks (no same 2 in a row) - any thoughts of how to try suppressors would also be welcome :-(.

Many thanks,
Shama

have you looked at your wiring between the plc system and the driver card?
it sounds like you may have a feedback loop in the analog circuitry.
when this happens the analog output will fail to work properly.
i'm sorry, this happened so long ago that i cannot remember the solution.
james

sjacobjf said:

I was in touch with Rockwell, and they had 2 ideas:

• Swap the slots of the plugins to see if that helped.
• Try suppressors on the outputs

Click to expand...

geniusintraining said:

have you tried moving your OF2 to a different slot on the failed PLC? How long were they installed before they started acting up?

Click to expand...

Maybe they read my post

For the surge suppressor, I have used a LOT of them from AD (Fuji)

https://www.automationdirect.com/ad...arts_-a-_accessories/surge_suppressors/sz-z35

I would also try and swap one out for a 48QWB, this will take a little rewiring but it maybe worth it

Thanks very much for your thoughts. I'll check out the surge suppressors. They aren't too expensive either, which is helpful.

It looks like 2080-LC50-48AWB is 120V input, 2080-LC50-48QWB is 12/24v input? Is this the only difference? Is it more stable? What are your thoughts on the swap? Lower voltage-less surge??

I have approximately 200 LC50's (QWB and QBB's) and they all have IF2 and OF2's installed and never had a issue with any of them, so since yours are the AWA (AC power and AC inputs) maybe there is something with the inner workings or a difference in the firmware that is causing the issue? Mine are also L24's not 48's but I dont think that would be an issue.

Yes the suppressors are cheap, did they recommend one?

geniusintraining said:

Maybe they read my post

For the surge suppressor, I have used a LOT of them from AD (Fuji)

https://www.automationdirect.com/ad...arts_-a-_accessories/surge_suppressors/sz-z35

I would also try and swap one out for a 48QWB, this will take a little rewiring but it maybe worth it

Click to expand...

What does the surge supressor do? I've seen many people recommend this on output cards, but never had to use one myself. Is it similar to a diode, helping current flow in one direction?

I did some basic research, and saw it is used to prevent voltage from rising from a certain level. But wouldn't having a fuse or circuit breaker do the same thing, but for the current instead of the voltage? From my experience, it is always best to add fuse or breaker between plc output card and device?

I found the OP's problem interesting as all the PLCs I look over don't have these suppressors, but if it helps, then maybe I should look into them for my own projects too?

Thanks,

alive15 said:

What does the surge supressor do? I've seen many people recommend this on output cards, but never had to use one myself. Is it similar to a diode, helping current flow in one direction?

I did some basic research, and saw it is used to prevent voltage from rising from a certain level. But wouldn't having a fuse or circuit breaker do the same thing, but for the current instead of the voltage? From my experience, it is always best to add fuse or breaker between plc output card and device?

I found the OP's problem interesting as all the PLCs I look over don't have these suppressors, but if it helps, then maybe I should look into them for my own projects too?

Thanks,

Click to expand...

The suppressor in the link is made to fit right onto Fuji contactor coils and is for use with 120VAC coils. It is the "RC" type meaning it has a resistor and capacitor. It will limit the inrush current when the coil first receives power as well as mitigate any spike that might occur when the output turns off. If you are driving inductive AC loads with a PLC using relay outputs or triac outputs, those surge arrestors are definitely helpful. Some of the early Micrologix 1000 with relay outputs definitely would experience faults that could be narrowed down to inductive loads spiking the relay outputs and adding surge suppressors often cured the issue.

There is a Tech Tip video on that page that starts off talking about DC coils but the principles are similar, and A/D sells suppressors designed for use with most of the contactors they sell with both AC and DC coils.

EDIT: here's part two of that video series that compares other types:
https://www.youtube.com/watch?v=r9KbxKsKHgU&ab_channel=AutomationDirect.com

I have only had to use them a few times and as Paul said try and limit the inrush and spikes.

AD does offer a lot of different ones and I was using their relay on that project, thats why I asked Shama if Rockwell suggested one that they recommended?

Thank you all for your thoughts.

Yes the suppressors are cheap, did they recommend one?

Click to expand...

No, they didn't recommend one - unfortunately. From what I can tell though, Rockwell's suppressors are quite bulky. Space is our biggest challenge in our current panels. We were restricted on panel size because they "ride" on a moving carriage, and space (and weight) are limited on moving equipment. The image below shows the top 1/2 of our panel. We have 8 solenoid valves, so the form factor has to be pretty small to fit all 8 suppressors.

We are planning to try some MOV's with an axial-type form factor - perhaps like the link below. In the current plan, one lead of the MOV would go into the terminal block shown lower right of the image below. The other lead would be soldered to a "rail" that would be connected to ground (which incidentally is close to the terminal block).

https://www.digikey.ca/en/products/detail/littelfuse-inc/V47MA2B/486035

The soleniod valves are 24vac, so we're planning to try around 30V max voltage and see how they do.

What do you think of the plan?

Yep thats tight... so is your OF2 common (198) isolated? have if yes have you thought about grounding it?

Can you put your suppressors out in the field vs at the PLC?

Yes, OF2 common (198) is isolated. Not sure on the grounding of 198, but the signal isolation board that it's connected to is grounded. If the isolation board is grounded, would you see a benefit to grounding 198 too?

The solenoid valves are also riding on the carriage, and in some cases are within a few inches of the back of the panel. So we kinda have 1 option, and that's inside the panel...

sjacobjf said:

If the isolation board is grounded, would you see a benefit to grounding 198 too?

Click to expand...

Not much but just wondering if there is some sort of noise being generated during the ride and I have seen poor grounding cause issues in the past... just thinking out loud

Ok sounds good. With 24vac solenoids, the mov that we're looking at (below) is rated for 30v with a 90v clamp. Does that sound reasonable?

https://www.digikey.ca/en/products/d...V47MA2B/486035

Looks like its a 13 week lead time?

Yes :-( Mouser has 69 in stock with more coming, so we should be able to get some in shortly to start working with.