RSLinx Classic OEM thinks PLC is still on when it's turned off

EngMan813

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Join Date
Oct 2018
Location
Florida
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11
Hello,

I'm a novice PLC user but advanced Excel VBA user. I've created a program to capture and email data from our PLC. The capture happens once an hour as it reads the tags in the PLC. Our second shift ends at 3:30AM on Saturday mornings and RSLinx isn't detecting when they shut the machines off for the weekend. It also doesn't detect when the PLC is turned back on for the morning shift start on Monday.

I read that there may be an issue with RSLinx where it loses it's "mind" or stops "auto-Browsing" if it doesn't detect a PLC for a period of time.

Is there a way to keep this auto browse alive even when PLC's are powered off? Like is there a "timeout" setting that can be changed in RSLinx to maintain the autobrowse longer?

I have VBA to look for tags to see if the PLC is online, but I have to uncheck and then recheck the "Autobrowse" checkbox to get RSLinx to see the state change in the PLC after the weekend.

It seems to be an issue for both PLC shutdown and startup.

I appreciate all your thoughts and responses.
 
Are you using a licensed RSLinx as an OPC Server? With named topics? The browser shouldn't matter there.
Sorry, I don't remember if RSLinx provides a connection status tag or not.
 
Yes, licensed version and utilizing DDE with named topics. RSLinx just seems to give up if it doesn't see the PLC after long periods of time (hours perhaps??).
 
Yes, licensed version and utilizing DDE with named topics. RSLinx just seems to give up if it doesn't see the PLC after long periods of time (hours perhaps??).

DDE has .... is the politically correct term 'issues'? ... determining communication status. It has a bunch of .. timers, timeouts .. not sure what to call them ... embedded inside the network layer. You don't have access to see them or to change them. Microsoft stopped talking about DDE support around 2004, when they started pushing OPC and DCOM.

If you are running a licensed RSLinx Gateway, you can make your VBA code a whole lot more complex, but *MUCH* more reliable, by using the support for OPC 2.0.

DDE is sort of like a message sent out by the source, with no feedback to the source on whether the message was received, or by how many receivers.

OPC 2.0 is more like open a named channel, set up a request for a list of tags, read the tags, and close the channel. You, as the guy that is receiving the data, know whether the channel is open, you get a fail code if it does not work, you can retry, you now how much data was received, etc. I've lost the technical details - I have not made one work except in a lab demo.

OPC 2.0 also has the option of building the list of tags, then requesting an update rate, and keeping the channel open .. or maybe you have one channel for the setup and one for the data being received ... I can't remember. It's more setup, but it is good for getting repetitive data and storing history.

Since you are requesting data once a day or so, I'd just to the open-request, receive, close method. And if the PLC is not accessible when your code is run, you WILL get an error message. And you can exit your code properly.

Sorry - I don't have example code. Rockwell is pushing the OPC 2.0 thing so your sales person or one of the technical guys should be able to dig out an example and send it to you.
 
Thanks thingstodo -

I've read several places where DDE isn't as reliable as OPC. I was, unfortunately, given the task of creating the Excel method (collect hourly, email daily results) with very little PLC knowledge. One of the other engineers here told me about DDE and gave me an example. I just ran with it.

I'm open to reprogramming with the OPC method, but I just would have no idea where to begin (i.e. what do I need to run on the PLC computer to get the communications - RSLinx?, what is the collections scheme....)

Not knowing if this will even fix the issue is the other side of the coin.

A bit more info that might spark additional thought:

My setup is this:

Laptop with RSLinx and Excel ---> Ethernet ---> PLC

The only time that I get issues is when the users shut off the PLC (connected to the UPS that they power down at end of 2nd shift on Saturday mornings. RSLinx doesn't detect that it's off and doesn't show the red X's. If I uncheck and recheck the "Autobrowse" checkbox, it refreshes and detects that the PLC is off. Its the same for power up on Monday mornings.

I'm looking for an open channel to the PLC, a hotlink to the "SurgeOK" as well as a "MachState" to see if it's online, and they are all "1's" until I uncheck and recheck the "autobrowse" then they go to the expected #N/A or #REF! state that I use to stop looking for data. Same at power up - they don't change until I physically uncheck and recheck the autobrowse box, then all is good.
 
My initial thoughts are that using Excel as a UI is not the way things are done. Probably for the reasons you mentioned. Use SCADA, or even a HMI.

Your VBA experience tells me you will be comfortable with AdvancedHMI. You could even get it to spit out an Excel file whenever you want, or make MUCH better user interfaces.

Cheaper than rslinx OEM too.
 
I use excel with with Linx Classic Gateway and the OPC server set to read a Micrologix 1400, I have the Micrologix 1400 reading messages from all my machines for the Data needed. I have it running constantly for years and is great. I use the ER bit for the first message to any of the other PLC's to latch a bit that stops the other messages for that PLC and the DN bit to unlatch it this notifies me that machine is off line.
I know how to bring data into the Excel for some of the use but have an another guy good with excel that wrote most of mine and it will email me different conditions.
 
Thanks AustraiIan -

Unfortunately, I was given RSLinx and asked to make it work. I'm close, I just can't seen to get it to know when the PLC has been turned off for a long period of time (weekend) and then turned back on. It just sticks with the last state even when "Autobrowse" is still checked.
 
@roxusa -

Any chance you might be willing to share your setup and sample Excel file? Obviously with any sensitive data removed.
 
what RSLinx are you using. In linx I create a topic and point it at my 1400
In RSLinx go to Edit It will drop down Copy DDE/OPC Link
Click that a box opens,expand left column& scroll down left side column and find your topic you created expand it and go to online,expand and find the data looking for in the PLC such as n7 double click it it will open on the right column
find the integer (example) N7:5, double click and say OK to close box.
Open Excel and right click a box and do Paste special, box opens keep unicode but check paste link, The live info from N7:5 is now running on that spread sheet
Try that and let me know
 
I create an Excel page to list all data I need to collect, Have to do One at a time but when done my guy uses data to make fancy bars and Graphs and formulas to display
 
Hi, I am not an expert with Factorytalk Vantagepoint, but with it you could probably achieve a much more reliable solution. If only one small spreadsheet it might not be worth the cost.
 
@roxusa -

I have no problem with creating hot links or gathering the data every hour with my VBA, the issue comes when they shut down the PLC's on the weekend. RSLinx stays running on the laptop that's connected to the machine via ethernet and it just hangs like it's still connected (no red X's). Since I use VBA in Excel to look at the @IsPresent hot link on my spreadsheet it thinks its still connected, but eventually exits the routine since the PLC is actually off.

It's the toggling of the hot link bit from the PLC through RSLinx. RSLinx just seems to not know how to handle when PLC's are shut off.

The spreadsheet and VBA I created works great all week when they leave things on, it's just detection of the off state of the PLC and then it returning to the on state.
 
Maybe I'm not experiencing that because the 1400 I collect from never gets turned of unless power failure. The production PLS's get turned off and my 1400 simply cant see them. I have RSLinx on auto brows and it never stops. I will test this weekend what happens if all PLC's on Linx are off a while.
 

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