defcon.klaxon
Lifetime Supporting Member
Hi guys,
I've come across a very odd problem that I can't figure out with testing communications failures and my 1756-L72 ControlLogix PLC with a 1756-ENBT ethernet module.
My master PLC polls remote PLCs (CompactLogix). Two remote PLCs are on the same copper network as the master; one is connected via fiber optic. The remote PLC with the fiber optic has a Profibus backup connection. I'm testing the failover code that switches from fiber to Profibus, and I'm coming across something very odd.
The way I test the fiber fail is that I pull the fuse for the media converter in the remote PLC's control panel. The comms fail code checks the value of "seconds since midnight" at each remote PLC, and if it doesn't update after a time delay, it activates a comms fail.
Oh, and as far as comms, I'm using MSG instructions. I do not have the remote PLCs in the I/O Configuration tree, I just use the IP addresses in the MSG instruction's configuration.
So, the odd thing I'm seeing is that when I create a comms fail at the remote PLC by pulling the media converter fuse, the master PLC errors out with *all* communications to the remote PLCs on the local, copper network. I then see "I/O Not Responding" warning in the status at the upper left of Logix; further, the 1756-ENBT module has a yellow triangle with a black exclamation point, and when I double click it to open it, it won't open and times out. The comms "blackout" lasts a couple of minutes. Then everything comes back and works perfectly, like nothing ever happened and the plant runs off the backup Profibus, and the copper connected remote PLCs get comms restored.
But here's the weird thing: if the ENBT module *truly* was timing out and couldn't be opened in Logix, wouldn't that mean I should lose connectivity to the PLC itself (I do not connect with USB, only ethernet)? So why would that module time out and not connect to any remote PLC, and not even let me open it in Logix, but it keeps my laptop online and I can watch code executing? And also, why would it eventually "clear up" and work as intended? Once it gets through that initial hang up, the comms come back exactly as you'd expect; timeouts at the one remote PLC, and perfect comms to the copper connected remote PLCs, and no hardware alarm/timeout in Logix.
This is a real head scratcher for me, and I feel like there many be something going on that I'm not aware of in the background of this module; or maybe it's faulty? Any insight into this would be supremely helpful. Thanks guys.
I've come across a very odd problem that I can't figure out with testing communications failures and my 1756-L72 ControlLogix PLC with a 1756-ENBT ethernet module.
My master PLC polls remote PLCs (CompactLogix). Two remote PLCs are on the same copper network as the master; one is connected via fiber optic. The remote PLC with the fiber optic has a Profibus backup connection. I'm testing the failover code that switches from fiber to Profibus, and I'm coming across something very odd.
The way I test the fiber fail is that I pull the fuse for the media converter in the remote PLC's control panel. The comms fail code checks the value of "seconds since midnight" at each remote PLC, and if it doesn't update after a time delay, it activates a comms fail.
Oh, and as far as comms, I'm using MSG instructions. I do not have the remote PLCs in the I/O Configuration tree, I just use the IP addresses in the MSG instruction's configuration.
So, the odd thing I'm seeing is that when I create a comms fail at the remote PLC by pulling the media converter fuse, the master PLC errors out with *all* communications to the remote PLCs on the local, copper network. I then see "I/O Not Responding" warning in the status at the upper left of Logix; further, the 1756-ENBT module has a yellow triangle with a black exclamation point, and when I double click it to open it, it won't open and times out. The comms "blackout" lasts a couple of minutes. Then everything comes back and works perfectly, like nothing ever happened and the plant runs off the backup Profibus, and the copper connected remote PLCs get comms restored.
But here's the weird thing: if the ENBT module *truly* was timing out and couldn't be opened in Logix, wouldn't that mean I should lose connectivity to the PLC itself (I do not connect with USB, only ethernet)? So why would that module time out and not connect to any remote PLC, and not even let me open it in Logix, but it keeps my laptop online and I can watch code executing? And also, why would it eventually "clear up" and work as intended? Once it gets through that initial hang up, the comms come back exactly as you'd expect; timeouts at the one remote PLC, and perfect comms to the copper connected remote PLCs, and no hardware alarm/timeout in Logix.
This is a real head scratcher for me, and I feel like there many be something going on that I'm not aware of in the background of this module; or maybe it's faulty? Any insight into this would be supremely helpful. Thanks guys.
