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Appendix A.2. The OPC Server – Limitations- Q&A
Q:How many fieldServers can one OPC Server communicate with?
A:Unlimited
Q: How many Clients can connect to the Server and how many points are possible?
A:Unlimited Clients & points, memory usage is about 2k/point/Client e.g.20 Clients with 10000 tags ea = 400MB. Server creates a thread for each Client, default each Client is looping thru 10000 tags every 25 ms looking for change of state. Such a config will probably flatten a 2G P4.
Q: Speed limitations?
A:The FS is the bottleneck at ~ 50 poll blocks/sec (to test set poll rate to 0)
e.g.. 2 FS total poll rate is ~100/s, if you have 10000 digitals in one DA on each FS that’s 2*50*10000 = 1 000 000 digitals per second.
Q: Remote Clients possible? Limits?
A:Yes I am running The Server & MB8PC under the debugger on my laptop, & Graphworx on another PC.
This is not recommended for complexity / reliability reasons.
Since the FieldServers are networked, rather run the Server on the Client machine - why bring a third layer in unnecessarily?.
When running remotely you should be able to OPC browse onto the Server machine, if this fails make sure that the OPCENUM service starts & runs on Server.
When running remotely the OPC Server is running under the app "dllhost.exe" in taskman. Because most Clients use OPC in asynchronous mode, the performance is almost indistinguishable for medium amounts of data.
Q:Is this an inprocess or out of process Server?
A:COM has 3 modes:- inprocess, local & remote
Local & remote have similar performance - the overhead of each COM call is 1000©s of times slower compared to inprocess.
Since this driver is capable of inprocess that should be used if option in your Client.
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.fieldServer.com Tel: (408)
