Kepware & VB

parky

Member
Join Date
Oct 2004
Location
Midlands
Posts
5,651
Hi Guys.
I'm developing a VB app to download a recipe from an SQL server to a mitsi q series plc, a Q25H using ethernet, however I have come across a rather puzzling problem, Kepware do not give much info on the opc DLL supplied & although I have it working if I read 2000 "R" registers with syncread it downloads them in about a second or two, however when I do a syncwrite of 2000 registers it takes about 2 minutes which is far too long.
I have not yet tried to monitor the packets but it apears that on a read it gathers all 2000 registers as one block but on a write it's as if it writes one register, verifies it the reads the next etc.
They are all in sequence i.e. R0 to R1999 Has anybody any ideas?
I know if I use the MX component the time is a great deal shorter but then again this is a direct driver.
 
I have never used that combo. However, in general you may want to check the Mitsi docs and find out what packed size they can handle and break your R/W into sizes that minimize packet fragmenting. Also is there an unmanaged switch or hub in the link that may be causing problems?
Just guessing?
 
I've done a similar application for a different PLC and also found that sync writes are very slow. In my case, verification of the written data was not critical, so I just switched to async writes.I also used array tags instead of multiple single tags. I don't know the limitations of Mutsubisi driver, if it allows reading and writing of 2000 tags at a time, it's great (for example, any Modbus-family protocol allows only 120 words at a time). See if you can create and write 200 tags of INT[10] type, i.e. each tag is an array of 10 consecutive words.

But sync writes in OPC are slow, that's a given, alas.
 
Well... been working on just those ideas myself & I've tried direct connection with crossover & split them into 100 word pockets & so far no difference at all.

The problem is that it has to be sync as the download must happen in one go as the master plc then writes the data to the relevant plc (any one of ten), the master sends the data over the NETH as a PLC send + I need to verify all transactions with checksum so cannot use async method as cannot rely on all data being there at the same time when I send the handshake & trigger signals.
It does not seem to matter even if i'm reading & writing other data from the kepware app, I've tride both on it's own & with 4,000 others reading & writing async mode (scada)the time difference isn't much greater.
The next thing is to break them into seperate channels on the kepware to see if that speeds it up or maybe I'll just fork out for MX Component. I know that does it in a second or two.
Anyway thanks for your feedback.
 

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