OPC Client - how to read from Remote OPC Server

Question

I used OPCDotNetLib but can't read data from remote OPC Server there .

I can connect , like

Type typeofOPCserver = Type.GetTypeFromProgID(clsidOPCserver, ip);

But looking the methods DataChanged or ReadCompleted doesn't work or works wrong.

I tested same with local OPC Server and it works well , with remote OPC Server I can connect, I can add items and can read data. OPC Server on remote machine shows that I read them, but I can't see any data. Seems like I need another workaround on OPCDotNetLib for remote OPC Server.

I even found a comment there

This library / dll will not work on a remote server, only local use is possible.

Is there some another available OPC Client .NET Libraries ?

Greg Buehler Greg Buehler · Accepted Answer · 2011-02-07T20:39:33

You've got a few options for OPC compatibility. You can use the classical COM wrappers provided by OPC Foundation, or you can use the newer OPC library designed for .Net.

I haven't personally switched over to the newer library yet, but this is a break down of how to use OpcNetApi.dll,OpcNetApi.Com.dll, and OpcRcw.Da.dll to initialize a connection and subscribe to the DataChanged event:

Opc.Da.Server scadaServer = null;
List<Opc.Da.Item> scadaItems = null;
Opc.Da.Subscription scadaSubscription = null;

string scadaUrl = string.Format("opcda://{0}/{1}", hostname,
                                                   opcServerVendor);

scadaServer = new Opc.Da.Server(new OpcCom.Factory(), new Opc.URL(scadaUrl));
scadaServer.Connect();

var scadaItems = new List<Opc.Da.Item>(); // I'm using a List<T>, but cast back to a simple array using ToArray();

// Repeat this next part for all the items you need to subscribe
Opc.Da.Item item = new Opc.Da.Item();
item.ItemName = TagPath; // Where TagPath is something like device.channel.tag001;
item.ClientHandle = handle; // handle is up to you, but i use a logical name for it
item.Active = true;
item.ActiveSpecified = true;

scadaItems.Add(item);

Opc.Da.SubscriptionState subscriptionState = new Opc.Da.SubscriptionState();
subscriptionState.Active = true;
subscriptionState.UpdateRate = 40;
subscriptionState.Deadband = 0;

scadaSubscription = scadaSubscription ?? (Opc.Da.Subscription)scadaServer.CreateSubscription(subscriptionState);

Opc.Da.ItemResult[] result = scadaSubscription.AddItems(scadaItems.ToArray());
for (int i = 0; i < result.Length; i++)
    scadaItems[i].ServerHandle = result[i].ServerHandle;

scadaSubscription.DataChanged += new Opc.Da.DataChangedEventHandler(OnDataChange);
scadaSubscription.State.Active = true;

OPC Client - how to read from Remote OPC Server

2 Answers