ModbusTCP Polling problem

[mariley2250]

I do alot of testing at work for the combustion systems that we manufacturer. I have used AHMI to mimic both our testing PLC and our DCS system. During our Factory Acceptance Testing (FAT) we have both BV and clients here to supervise the testing. The idea behind using AHMI is to make it more graphical and to be a more realistic type of testing, basically have the feel of what it will be once the equipment is commissioned on site.

My problem at the moment is that i am trying to poll roughly about 300-400 modbus TCP points. Even with the poll rate down to its lowest setting the modbus is terribly slow. What i have worked out is that it seems to illiterate through each point polling them one by one. Is there a way in which i can poll all 300-400 points in one go. I know this is possible with a modbus polling software but i am after the graphical content for the customers benefit.

Thanks 

[Archie]

If you edit ModbusBase.vb and go to line 515:

((SubscriptionList(index + ItemCountToGroup + 1).Address.Element + SubscriptionList(index + ItemCountToGroup + 1).Address.NumberOfElements) - SubscriptionList(index).Address.Element) < 20 AndAlso


The value of 20 is a maximum address span. If your device allows 100 element reads in a single read, then change the 20 to a 100

[mariley2250]

Hi Archie,

Thanks for the info. Fixed up half of my problem. It seems as though now once it grabs the modbus data it illiterates through each individual item to change the status of it. There is about 3-4 second delay. Is there any other values you can think of that can be change to minimize this time further??

Thanks

[Archie]

Once the data is retrieves, the processes of distributing it out to subscriptions should only take milliseconds. Unless you are using DataSubscribers that has code that takes a long time to process.

[mariley2250]

definitely not using datasubscribers and its still very slow. could it be lag in the PLC??