KepServer and Modbus

mrtweaver

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Join Date
May 2007
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Bloomsburg
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I was wondering, in the line of KepServer, if you are using the Modbus Ethernet driver. I have been doing a lot of reading on Modbus and they talk about Masters and Slaves. We are also still running the product in the demo mode. So with all that being said I was wondering if anyone more familiar with both of these could answer the following questions.

1. Because of running KepServer in the demo mode, does this have any effect on the number of devices/channels that can run concurrently?

2. Because of the issues with master/slave configurations can you have more than one master on a network?

3. Can more than one master talk to one slave? IE: if you have two slave devices and two copies of Kepserver running can both copies of Kepserver talk to both slave devices at the same time.

4. This is probably a timing issue but lets say you configure 99 channels with each supporting its own device and own IP channel. Would this cause channels that are connected to the network to go to offline and report bad connection and bad data? So would this be a connection timing issue or because of the master slave issues with Modbus?

Out of the 99 channels/devices I have configured only about 10 are online at this time. So Like I asked I dont know if this is a timing issue with Kepserver, a problem because of modbus master/slave issues, an issue because of still running kepserver in demo mode, or because of running it on Win XP, or what? I am planning on trying to run it on our dedicated server and seeing what happens but I know right now running it on XP sometimes it connects sometimes it does not and it is very erratic.

So any thoughts greatly appreciated. Have a great day.
 
mrtweaver said:
1. Because of running KepServer in the demo mode, does this have any effect on the number of devices/channels that can run concurrently?
No. The only limitation for KEPServer demo mode is that it will shut down after two hours. After which it can be immediately restarted for another two hours. A side effect of this is that you cannot run unlicensed KEPServer as a service.
2. Because of the issues with master/slave configurations can you have more than one master on a network?
As long as several masters don't try to communicate with the same slaves simultaneously, yes. In addition, some slaves, once connected to by a master, do not release their connection nicely so it would be hard to connect to them from another master - I have seen this kind of behavoir on Cognex In-Sight vision cameras.
3. Can more than one master talk to one slave? IE: if you have two slave devices and two copies of Kepserver running can both copies of Kepserver talk to both slave devices at the same time.
Each master can talk to each slave but two masters cannot talk to the same slave simultaneously. Think of it as a virtual serial line.
4. This is probably a timing issue but lets say you configure 99 channels with each supporting its own device and own IP channel. Would this cause channels that are connected to the network to go to offline and report bad connection and bad data? So would this be a connection timing issue or because of the master slave issues with Modbus?

Out of the 99 channels/devices I have configured only about 10 are online at this time. So Like I asked I dont know if this is a timing issue with Kepserver, a problem because of modbus master/slave issues, an issue because of still running kepserver in demo mode, or because of running it on Win XP, or what? I am planning on trying to run it on our dedicated server and seeing what happens but I know right now running it on XP sometimes it connects sometimes it does not and it is very erratic.
It's a murky thing. Obviously, the more slaves & channels are communicating, the more data is read and the smaller the update time is, the more network bandwith and CPU time is being used. This is a trial and error thing: you would have to play with the settings in order to see how many channels at the time can you reasonably communicate on. I have never done that type of thing so I cannot be specific. However, if given a task to do continuous data collection using KEPServer, I would initially plan for no more that 10 slaves per server (i.e. 10 PCs/licenses for 100 slaves). Maybe it is too conservative and overly cautious.
 
So your recomendation would be have multiple copies of KepServer running and each copy would watch 10 slave(plc) devices.

Just a little fyi. Like I said I will have 99 devices online and each device will have about 60 tags. For a grand total of about 6000 tags total.

Now given this piece of info and seeing what ladderlogic wrote are there any other suggestions? Is anyone else using KepServer and watching a multitude of PLC with an equivalent amount of tags? If so did you have multiple copies of KepServer?

Thanks for any all info. Have a great day.

LadderLogic said:
No. The only limitation for KEPServer demo mode is that it will shut down after two hours. After which it can be immediately restarted for another two hours. A side effect of this is that you cannot run unlicensed KEPServer as a service.

As long as several masters don't try to communicate with the same slaves simultaneously, yes. In addition, some slaves, once connected to by a master, do not release their connection nicely so it would be hard to connect to them from another master - I have seen this kind of behavoir on Cognex In-Sight vision cameras.

Each master can talk to each slave but two masters cannot talk to the same slave simultaneously. Think of it as a virtual serial line.

It's a murky thing. Obviously, the more slaves & channels are communicating, the more data is read and the smaller the update time is, the more network bandwith and CPU time is being used. This is a trial and error thing: you would have to play with the settings in order to see how many channels at the time can you reasonably communicate on. I have never done that type of thing so I cannot be specific. However, if given a task to do continuous data collection using KEPServer, I would initially plan for no more that 10 slaves per server (i.e. 10 PCs/licenses for 100 slaves). Maybe it is too conservative and overly cautious.
 
I'd contact Kepware with your specific requirements. They'll be able to best tell you what a single installation of KepServer Ex is capable of, and provide recommendations for Modbus Master/Slave options. In the past I've been able to get through to them easily.

mrtweaver said:
So your recomendation would be have multiple copies of KepServer running and each copy would watch 10 slave(plc) devices.

Just a little fyi. Like I said I will have 99 devices online and each device will have about 60 tags. For a grand total of about 6000 tags total.

Now given this piece of info and seeing what ladderlogic wrote are there any other suggestions? Is anyone else using KepServer and watching a multitude of PLC with an equivalent amount of tags? If so did you have multiple copies of KepServer?

Thanks for any all info. Have a great day.
 

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