The IdOPCBrowser interface is an optional interface. It it not necessarily supported by OPC custom interface servers. If an OPC custom interface server does not implement the browse interface, no TdOPCBrowser object will be returned.
var
Server : TdOPCDAClient;
begin
Server := TdOPCDAClient.Create(nil);
Server.ServerName := 'Matrikon.OPC.Simulation';
Server.Active := true; //connect to Server
Server.Browser.ShowBranches(Memo1.Lines)
Server.Active := false; //disconnect from Server
Server.Free;
end;