thingstodo
Member
I’m working on getting a Parallel Redundancy Protocol PRP system set up in a lab situation. The L73 PLC is in rack 4. 3 io racks are 1,2,3.
I have posted about this system in the past. See thread https://www.plctalk.net/qanda/showpost.php?p=937884&postcount=1
An update to the comments from the previous thread, Rockwell network engineers have reviewed a newer version of the sketch and approved it as a PRP network. It appears to follow PRP rules.
So parts were ordered, and have eventually arrived.
We’ve got some hardware, connected it together, and it’s working. I’m looking to detect failures and alarm them before they cause process issues (equipment stops running due to communication failure).
Racks 2 and 4 have a 1756-EN4TR set to mode 4 (PRP). Racks 1 and 3 have 1756-EN2TP.
All 4 racks each have 2 cat6 copper connections, Channel A to a Stratix 5400 switch and Channel B to a Stratix 5410 switch. The IT guys have not decided on the config for the Stratix switches as yet. The communications works just taking the switch out of the box, powering it up, and plugging in the RJ45 cat6 cables. Since the switches do not have IP addresses as yet, I can’t use the AOI to show which ports are up, get the temperature of the switches, see that only one power supply is working, etc. I’ll get there when IT gets the switch config nailed down. I believe that stuff is available from the AOI for the Stratix.
For now, the racks appear to communicate fine this way. We have redundant power supplies for each switch, redundant cabling to each EN2TP and EN4TR.
For all single points of failure the rack status for the input cards is solid - I can disconnect one cable at a time from an EN2TP or EN4TR, power down one switch, power down a power supply. No communication problems. This is as expected.
I’m trying to figure out how to detect when one of the above single points of failure has occurred so that it can be alarmed and someone can go fix it before a second failure takes down the process. I’d like to alarm when a network cable is cut or is experiencing retries, CRC errors, Frame errors, etc that indicate a cabling problem. Or when Port A or Port B on a particular EN2TP or EN4TR has no link, is not active, etc.
So far, going through various manuals I have found two recommended messages to each rack as below. But there is no doc for what the bits in the returned DINT mean:
Message type: CIP Generic
Service Type: Get Single Attribute
Class: 56
Instance: 1
Attribute: 11
Destination Element : a DINT for each message
Attribute 11 gets A port status, Attribute 12 gets B port status, that's why there are 2 messages to each.
I can't locate any documentation from Rockwell that tells me what the bits in the message above (destination DINT) represent. I had high hopes that I could alarm any single failure in the ethernet cabling using these messages.
I am monitoring the message instructions for .ER, but that error bit seems to take 30 seconds or more to detect an unplugged ethernet cable. If the ethernet cable is not totally disconnected for the entire time (RJ45 is unplugged, then plugged back in within 30 seconds), the message goes through and there is no .ER on the message. 30 second timeout seems to be
fast enough for a cut cable but it doesn’t appear to see an intermittent cabling problem.
Am I just being too paranoid?
Is anyone alarming issues with PRP and is willing to share?
I have posted about this system in the past. See thread https://www.plctalk.net/qanda/showpost.php?p=937884&postcount=1
An update to the comments from the previous thread, Rockwell network engineers have reviewed a newer version of the sketch and approved it as a PRP network. It appears to follow PRP rules.
So parts were ordered, and have eventually arrived.
We’ve got some hardware, connected it together, and it’s working. I’m looking to detect failures and alarm them before they cause process issues (equipment stops running due to communication failure).
Racks 2 and 4 have a 1756-EN4TR set to mode 4 (PRP). Racks 1 and 3 have 1756-EN2TP.
All 4 racks each have 2 cat6 copper connections, Channel A to a Stratix 5400 switch and Channel B to a Stratix 5410 switch. The IT guys have not decided on the config for the Stratix switches as yet. The communications works just taking the switch out of the box, powering it up, and plugging in the RJ45 cat6 cables. Since the switches do not have IP addresses as yet, I can’t use the AOI to show which ports are up, get the temperature of the switches, see that only one power supply is working, etc. I’ll get there when IT gets the switch config nailed down. I believe that stuff is available from the AOI for the Stratix.
For now, the racks appear to communicate fine this way. We have redundant power supplies for each switch, redundant cabling to each EN2TP and EN4TR.
For all single points of failure the rack status for the input cards is solid - I can disconnect one cable at a time from an EN2TP or EN4TR, power down one switch, power down a power supply. No communication problems. This is as expected.
I’m trying to figure out how to detect when one of the above single points of failure has occurred so that it can be alarmed and someone can go fix it before a second failure takes down the process. I’d like to alarm when a network cable is cut or is experiencing retries, CRC errors, Frame errors, etc that indicate a cabling problem. Or when Port A or Port B on a particular EN2TP or EN4TR has no link, is not active, etc.
So far, going through various manuals I have found two recommended messages to each rack as below. But there is no doc for what the bits in the returned DINT mean:
Message type: CIP Generic
Service Type: Get Single Attribute
Class: 56
Instance: 1
Attribute: 11
Destination Element : a DINT for each message
Attribute 11 gets A port status, Attribute 12 gets B port status, that's why there are 2 messages to each.
I can't locate any documentation from Rockwell that tells me what the bits in the message above (destination DINT) represent. I had high hopes that I could alarm any single failure in the ethernet cabling using these messages.
I am monitoring the message instructions for .ER, but that error bit seems to take 30 seconds or more to detect an unplugged ethernet cable. If the ethernet cable is not totally disconnected for the entire time (RJ45 is unplugged, then plugged back in within 30 seconds), the message goes through and there is no .ER on the message. 30 second timeout seems to be
fast enough for a cut cable but it doesn’t appear to see an intermittent cabling problem.
Am I just being too paranoid?
Is anyone alarming issues with PRP and is willing to share?