Device Net Faults

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Using Allen Bradley PLC, two Device Net Cards, AB PhotoEyes and Magnetek 333 AC Drives. The shop is broken up into two parts for the Device Net cards: (Front Half on one card and Back Half on the other card). The 24 V DC is find on the whole shop.
We lose communication to the Magnetek 333 AC Drives and that card will Fault and we lose half of the shop. We are looking into redoing some parts of the shop.
What I would like to do is program the PLC to Log the Node of the Drive or Eye that has lost communication and try to reconnect to them lets say x number of times. After the x time tring to reconnect and it does not can that drive or eye be isolated so it will not Fault the system but give an alarm? Any other ideas are welcomed.
email: [email protected]
 
We just installed a DeviceNet system that suffered similar problems, we had to change the power supply from a single output to a dual. We suffered comm problems with drives and/or loss of devices on network.

Cant say if you can do what you want or not, seems to me that if the card faults with loss of communication then you would have to prevent that for x number of times to try to reestablish comm, check the card and it may have that feature.

Best thing to do is determine WHY it is losing communication.
 
Which type of A-B scanner are you using? The different models of scanner module have different diagnostic abilities; I just did a bit of error logging on a 1756-DNB but it's a little less sophisticated with the 1747-SDN or 1771-SDN.

If you're getting a "Bus Off" error on the scanner (Error Code 91 displayed on the Status Display), then the whole darn network is "crashing", you need to do a closer physical inspection for termination, noise, shielding, and power.

Nick Jones wrote a couple of good DeviceNet physical troubleshooting documents and they're on SST's "DeviceNet Alert" website:

http://www.mynetalert.com/education.htm

It's nearly a mantra on the technical support phones : "voltage, termination, shielding. Voltage, termination, shielding."

From your original post, it sounded like you might have a single power supply for both networks; you should have just one power supply per network. If the trunklines aren't connected together, then the power supplies shouldn't be, either.

Any more info you can give on the model numbers and configuration of the network would help, too !
 
faults

Thanks for the help we will look into it closer. The shop was configured and programed by a vendor. Two to three power supplies for both networks.
 
I happen to have a free afternoon and a deskful of SLC-500 and DeviceNet hardware... let me know which model of controller and DNet scanner and I can give you a program example for how to trap the error codes on the DeviceNet scanner.

That's one of the hard things about troubleshooting; the maintenance guys say "it broke" but are hard-pressed to say if the LED was green or red. Programming simple logic traps can help a lot to improve the memories of the graveyard shift.
 
THANKS KEN. I will look into the model of controller and DNet scanner and get back to you Tuesday for that program example.

Thanks again.
 
Related...

Many moons ago, we were suffering buss-off on our devicenet system, and I got a whole host of useful infor from you guys for troubleshooting it. Thanks to all who contributed!

To bring it up to date - and since it's related - I slapped some capacitors across the power supply for extra filtering, and the problem disappeared for months. Then, just last week, it resurfaced with a vengeance.

We roke down and got an SST Netalert Netmeter. Picked that model for it's ease of use (knew what I was looking for and how to find it in about 20 minutes) and the fact that our devicenet card is also an SST, so expected good customer service.

Got it on all counts. Found my readings, got help interpreting them and took action. Turns out one of our welders was generating excessive noise, even when it wasn't welding! Sucker was causing faults throughout the system on every node, totaling up to 100 / second. Cut the welder out, and errors / sec dropped to zero (123 er / sec causes buss-off).

Replaced the welder - no more issues. I am a happy tech!

If you have devicenet in your shop, swallow your pride - and the $1000 price tag - and get a netmeter, if not the Netalert, then something else. This little baby is going right to the top of my must-have tools list :)

TM
 
We have a DeviceNet network at our plant that runs between two buildings. It is the network that we have the most problems with (i.e. fault 91, bus-off). We have seen it caused by corrosion in the connectors on the trunk line and water damage in the Device Link nodes due to the covering breaking down from UV exposure.
 
I agree with Moulder's reply. I have a Net Alert (looks like a handheld DMM) and I found it invaluable for both system commissioning and troubleshooting down the road.

What is your baud rate (125, 250, 500)? Did the installer use proper DeviceNet cable? Are there terminating resistors? Are they properly placed on the network? If there are multiple power supplies on the networks, are they isolated from each other? Do you know how much current the Magnetek drive interface cards consume? Is your network properly shielded?

Obviously, you must begin by going back to the original design to determine if it was done properly, then view your as-builts to verify that it was done as designed. I have found a properly designed and installed DeviceNet network to be very reliable and robust.

What happened to the original vendor/designer? Are they not able to help?

Good Luck. Dennis B.
 
Ken,
I would love to see some examples of trapping error codes. I have a micrologix 1500 using a 1769 SDN connected to a 1794 flex rack. I also have a softlogix (5000) processor using a 1784 PCIDS scanner connected to another 1794 flex rack. so examples in 500 or 5000 would be awesome.

thanks!
 

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