DeviceNet Choke?

[sthompson]

Stu, To answer your questions:
1 Yes
2 No it shares a PS with the panelview
3 The scanner and 3 drives in one cabinet, the other three in another cabinet 3" below the first cabinet (don't ask)
4 Roughly 10-12 feet total cable length at the most.
5 I quess I'd say looped from drive to drive.
6 Thin cable
7 125Kbs baud rate

Ken,
1 To clear the "78" fault we cycle power to the drive.
2 I checked the program again to make sure that nothing is over-writting the M File for the Scanner.
3 There aren't any buttons wired to the drives.
4 Can I tie TB3-3 to the cabinet ground? Everything in these cabinets shares the same ground.
5 How is grounding TB3-3 different using the ground screws on the drive?
6 It will take me a day or two to get some logic traps programmed in to check for fault code number and duration.

Sportster:

Wow! My compliments, it is rare that we actually get timely and useful answers. If we even get an answer at all.

For the distance you are running, I don't see a big problem with your setup. Ken may see something I am missing.

In regards to the Power Supply, you wouldn't think there should be a problem, but the PanelView HMI might have a Switching Power Supply inducing noise on the 24VDC. I always put my Devicenet on its own Power Supply. Do you have a spare 24VDC Power Supply you could put on either the HMI or the Devicenet to see if the problem goes away? If you have an Oscilloscope you might want to have a look on the 24VDC Lines.

I also loop my VFDs in Cabinets in free air, and keep the cable out of the Wireway so that it is not exposed to the noise generated by the VFD T-Leads. Is that the case here, or is the Thin Cable mixed in with the VFD wiring?

How often does this problem occur, once a day, once a shift, sporadically, or multiple times then a period where it runs ok?

Also, what CompactLogix PLC and Firmware Version are you using? I presume you are using RSNetworx for Devicenet, and the matching RSLogix5000.

You Mentioned M Files, are you communicating with the VFDs through the M Files rather than mapping them as I/O? How are you sending Commands and reading Status from the VFDs?

Stu......

 

[sportster]

Stu,

1 I do have a spare PS and will check the lines on the existing one with our o-scope when I get to work this afternoon.
2 The DNet cable is hanging in free air except where it passes through the conduit nipple to the other cabinet. There aren't any other wires in that conduit.
3 The problem is very sporadic. It might happen a couple times in one shift and then not happen for a day or a week. Sometimes it happens just once. Sometimes it happens a few times a shift for two or three shifts in a row. Sometimes it takes powering down the drive with the "78" fault several times before it comes back to life and communicates.
4 No Compactlogix; it is a Micro1500. And I mis-spoke; we are using the regular Input and Output files for communication. (Had two problems/projects running through my head while typing)

Patrick

 

[sthompson]

Stu,

1 I do have a spare PS and will check the lines on the existing one with our o-scope when I get to work this afternoon.
2 The DNet cable is hanging in free air except where it passes through the conduit nipple to the other cabinet. There aren't any other wires in that conduit.
3 The problem is very sporadic. It might happen a couple times in one shift and then not happen for a day or a week. Sometimes it happens just once. Sometimes it happens a few times a shift for two or three shifts in a row. Sometimes it takes powering down the drive with the "78" fault several times before it comes back to life and communicates.
4 No Compactlogix; it is a Micro1500. And I mis-spoke; we are using the regular Input and Output files for communication. (Had two problems/projects running through my head while typing)

Patrick

Patrick:

Well, that is what happens when you assume, I saw the 1769 and I was thinking CompactLogix. Is there anyway you can post the RSS File for the PLC Program, and your RSNetworx File for the Devicenet?

Stu.....

 

[sportster]

Stu,

Here are the Logix500 progam and the DNet configuration zipped in one file.

 

[BobB]

DN uses a 120 ohm resistor as a terminator - like most comm lines.
GE-Multilin (protection relays) recommend for Modbus RTU connections that the terminator be a 120 ohm resistor with a 100 puff ceramic capacitor in series. I have found it works very well for me and use it quite regularly on all comm lines.
Carry the resistors and capacitors in the laptop bag all the time - along with 5k, 1ok, 50k etc for all sorts of funny things like generator controllers etc.
Check it out in the GE-Multilin manual for the SR489 generator protection relay for example - beware - huge manual.

 

[gmferg]

Proper DNET Grounding

One more check to add to the list: Your thin cable shield and V- must be grounded at one place only. Typically the best place is at the power supply.


We recently had same symptoms on one of our new installs and found that the electricians forgot to install jumper between V- and shield when transitioning from flat to round cable.



This is from Dr. Dnet's (Robert Law) Bible, a must read: