adccommunitymod (AutomationDirect) asked a question.
Fail Safe due to LAN connection
Created Date: September 10,2019
Created By: aroja164
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Hi All, I connect my water tank and its sensors to PLC and it is working fine now. I connect the PLC through LAN port to my computer. Is there any way to detect LAN connection, so that if the PLC detect there is no connection from the LAN, my actuator valve and pump will be forced to close by the PLC. This is important, for example, by accident or by mistake someone in my lab take off the LAN cable, I want to stop the tank-PLC operation. Any help would be appreciated. Thank you.
Created Date: September 10,2019
Created by: aroja164
Hi All,
I connect my water tank and its sensors to PLC and it is working fine now. I connect the PLC through LAN port to my computer. Is there any way to detect LAN connection, so that if the PLC detect there is no connection from the LAN, my actuator valve and pump will be forced to close by the PLC. This is important, for example, by accident or by mistake someone in my lab take off the LAN cable, I want to stop the tank-PLC operation.
Any help would be appreciated. Thank you.
Created Date: September 10,2019
Created by: MikeN
What PLC do you have?
I do an internet check every hour on a BRX very easily, and if the internet check fails I have it run a LAN check and then it will generate an alarm based on whether only the internet connectivity is down or if it is a local network problem.
I have not done this on a Productivity or DL before though. Easiest in Do-More because you have very nice instructions ready to go for Ping that you can use. Ping a google DNS server for internet check, ping your local router for LAN check.
I assume you can have a tag in Productivity that says whether the ethernet port is active or not. If you lose access on lan to the local switch it is plugged into that would tell you whether the lan is down or not.
Created Date: September 10,2019
Created by: aroja164
Hi MikeN,
I am using P1000, P1-540.
Created Date: September 10,2019
Created by: MikeN
In the CPU module there is an "Ethernet Heartbeat Timeout Bit " that you should be able to use to know whether the LAN has a connective active or if it dropped.
Created Date: September 11,2019
Created by: aroja164
Hi MikeN,
I tried something like this, but it only turned off the DO-0.1.2.7, because what I want to achieve is that when the LAN cable is disturbed then DO-0.1.2.7 must be turned ON, and if the LAN Cable works normally then DO-0.1.2.7 must be turned OFF.
I tried the "Ethernet Heartbeat Timeout Bit " { "data-align ": "none ", "data-size ": "full ", "title ": "Capture7.JPG ", "data-attachmentid ":125085}
Created Date: September 11,2019
Created by: kewakl
RE: Ethernet heartbeat help topic P282 - Options Tab Configuration bullet point (m)
This bit only applies when the CPU ports are being used as a slave device and only monitors the time between the communications from the master device.
When you do design a viable method for detecting a disconnected ethernet cable, use a timeout to minimize nuisance tripping.
Created Date: September 11,2019
Created by: MikeN
If the timeout bit only works in some situations then maybe the port ready bit along with a timer could be used to detect a timeout. Normal traffic on a PLC has periods between activity where the ready bit will be on, so if the ready bit stays off for maybe 2-3 seconds straight then it could be assumed that the cable is not connected
Created Date: September 11,2019
Created by: kewakl
It seems that bit of testing will be needed.
will 'port ready ' be true if the plc is only connected to a switch? Or does there need to be a src/dst comms device?
hopefully an ad tech will chime in.
Created Date: September 11,2019
Created by: MikeN
I just looked at my test bench and "port ready " does sit on when the PLC is only connected to a switch and there is nothing at all set up for com traffic.
Created Date: September 11,2019
Created by: aroja164
Hi,
Thank you for your comments.
I also tried something like this. But is only turn on the DO-0.1.1.7 and the DO-0.1.1.7 stays ON when I unplugged the LAN Cable. So is it possible to do Fail-Safe operation only by using 1 PLC connected to PC without slave? I know that there is a tutorial on how to do Master-Slave PLCs and one of them checking the connection to the other.
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