You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old August 28th, 2012, 04:35 PM   #1
Rob S.
Member
United States

Rob S. is offline
 
Join Date: Sep 2008
Location: Maryland
Posts: 690
Dog Random Plant stoppage, I question DeviceNet network.

The last two days our automation has just stopped randomly at different spots. Everything that has stopped, is thru DeviceNet.We have about 5 faults on our HMI ( Panelview Plus )at the same time. Digging deeper into the faults, I took notice that they are faults dealing with a air cylinder ,reed switch, or motor not reaching a prox , etc. that has to reach that in a certain amount of time , or it will fault out.

I am thinking that the program is still running , but the DeviceNet Flex I/O is losing comunication for a split second.

I am not getting any DeviceNet faults. Do you think I am on the right track ? Have any of you had a DeviceNet network that has somewhat brokendown ,after being in service for a few years ?

Thanks in advance , have a great evening.
  Reply With Quote
Old August 28th, 2012, 05:09 PM   #2
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 15,218
How are you detecting and trapping DeviceNet errors/faults ? What type of DeviceNet scanner are you using ?

DeviceNet uses a standard "4x RPI" timeout value. If you're using Polled I/O, and there are four Polls by the Master that are not responded to, the Master declares a timeout.

Similarly, if you are using Cyclic I/O connections, the Master declares a timeout after more than 4x the RPI has gone by without a reply from the slave.

After a Timeout has occurred, it takes between 1 and 4 seconds for a DeviceNet scanner and a FLEX adapter to re-start the connection. This is plenty of time for ladder logic to trap a fault bit, but too fast for most folks to check the scrolling display on the scanner.

It's certainly possible for a DeviceNet network to degrade over the course of a few years, just like any electronic system with field terminated wires. Corrosion, vibration, or increased noise on the system could start causing CAN network errors, and those could start causing I/O connection timeouts. Such problems absolutely will show up using a Woodhead NetMeter.

What's very unlikely is for the system to be able to have enough packet errors to miss I/O signals without also generating I/O Connection faults that can be trapped and diagnosed.

Is there anything else the I/O points have in common; a common DC supply or DC Common wire that might have loosened or failed ?

Be thankful the operators aren't describing this as a "PanelView fault" because the error messages are displayed on the PanelView.
  Reply With Quote
Old August 28th, 2012, 07:10 PM   #3
Rob S.
Member
United States

Rob S. is offline
 
Join Date: Sep 2008
Location: Maryland
Posts: 690
I plan on purchasing a Woodhead NetMeter tomorrow. I read the manual a little before leaving the plant. I didn't see a discription of how to actually hook it up to the network. Is there any better discription on how to hook it up?

It seems like a difficult problem to solve ,being so random.

Thanks for your help,
  Reply With Quote
Old August 28th, 2012, 08:03 PM   #4
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 15,218
The NetMeter comes with some tap cables that are meant for plugging into Mini and Micro quick-disconnects.

I frequently installed short drop cables for analyzer access, and made up my own cable with an open-style Combicon female socket. This would allow me to plug in either the NetMeter or my 1784-PCD for protocol analysis.

The NetMeter frequently does its job by showing no errors ! If I'm investigating a DeviceNet and it goes through a device failure but there are no CAN errors on the bus, I know that the device itself should be investigated, rather than the network.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
weird and cursed devicenet network darkest_shade LIVE PLC Questions And Answers 11 July 29th, 2008 12:55 PM
Random DeviceNet Nodes dropping off Network MorphuisOGrady LIVE PLC Questions And Answers 18 July 24th, 2008 03:13 PM
Micrologix on Devicenet network? oregonsam LIVE PLC Questions And Answers 7 August 17th, 2006 08:12 AM
Mitsubishi VFD DeviceNet Question alphageek LIVE PLC Questions And Answers 1 March 26th, 2005 01:52 PM
Dh-485 Network Question mattbdb LIVE PLC Questions And Answers 3 July 20th, 2004 11:30 AM


All times are GMT -5. The time now is 08:58 AM.


.