CLX, adding a computer to the IO tree

I am trying to monitor the comms between a 1756-L71 and a basic computer. The pc is running FTView ME with an HMI. I need to verify comms are up and running. I think the Generic Module will work but unsure of all of the assembly instance and size configurations. Has anyone tried this before or do I just need to play with the numbers and download until I find the right settings?

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An RSLinx Classic or RSLinx Enterprise station won't accept a cyclic I/O connection, even with a long RPI or zero size, so the I/O tree isn't the right way to do this.

And the explicit message connection tables that are shown in the ControlLogix Ethernet module's web page aren't easy to access or decipher.

I have used two other methods to accomplish that task:

1. In FactoryTalk View ME, use a Global connection to send the /Seconds HMI tag to a tag in the ControlLogix, and write simple watchdog logic that detects if that value remains the same for more than a couple of seconds. That will show you that the HMI is both turned on and connected, and the FTView ME is running.

2. Send a repeated MSG instruction to the PC's IP address with the "Get Identity" service. RSLinx will respond with its identity information, allowing you to confirm at least that RSLinx is up and running.

Wouldn't it make more sense to have the PC check if the PLC comms are active ? What do you want to happen if communication is lost ? Ideally people prefer an alarm on the HMI.

You could setup the PC to check by running a script to ping the PLC IP or maybe setup a heartbeat/watchdog system. Not sure what's the right way but it would probably be easier than checking from the PLC.

We run a redundant PLC system that allows both PLC's to monitor changes in the logic. If the "primary" plc fails it automatically changes the IP address of the ethernet cards and allows the "secondary to assume control. Currently we use system values from managed ethernet switches to perform this function. We have a few clients that would like to get away from the managed switch usage and i have been given the task of developing the new platform. I am currently using the hmi seconds pulse and will probably have to go that route. was just wondering if it was possible to add in the pc as a module and use a "GSV" for monitoring instead.
thanks for the info.

trapelj said:

We run a redundant PLC system that allows both PLC's to monitor changes in the logic. If the "primary" plc fails it automatically changes the IP address of the ethernet cards and allows the "secondary to assume control. Currently we use system values from managed ethernet switches to perform this function. We have a few clients that would like to get away from the managed switch usage and i have been given the task of developing the new platform. I am currently using the hmi seconds pulse and will probably have to go that route. was just wondering if it was possible to add in the pc as a module and use a "GSV" for monitoring instead.
thanks for the info.

Click to expand...

Are you running a controllogix redundancy? I'm trying to figure out what you're trying to watch, because the switchover is so fast you shouldn't notice it. There are GSVs to tell you if you have switched over, the status of the secondary, etc. etc. Is that more what you're looking for?

That doesn't sound like ControlLogix Redundancy; did this system pre-date ControlLogix Redundancy, or was it done for commercial or technical reasons ?

>we have a few clients that would like to get away from the managed switch usage

Do you mean that they want to rely on the ControlLogix instead of the managed switch, or that they want to use un-managed switches in this high-availability control system instead ?

I wish the ControlLogix Ethernet modules made more connection information easily available to the user program, but they really leave that stuff in the background instead of allowing the user program to try to make use of them. The best mechanisms for probing the HMI connection remain watchdogs and identity object reads.

PLC to PC comms

It is a redundant system but we use information currently gathered from managed switches to determine which rack will become the primary controller. Pri rack IP is x.x.x.201 and SEC rack IP is x.x.x.202. Whichever rack is primary automatically changes the first ENBT(ethernet card) from its default IP to the primary IP(x.x.x.200). We currently use the Global connections (seconds) to monitor if the PC is alive. The PCs we use have two NIC cards. I am trying to develop a way of ensuring that both connects are alive to the PC. This information is used for the graphics, single line diagram, on a network overview. I am tasked with cutting initial startup cost and getting rid of a bunch of managed switches is a big start.