List<DAItemGroupArguments> dAItemGroupArguments = new List<DAItemGroupArguments>();
 public void subscribe_items(string ip)
        {             
            dAItemGroupArguments.Add(new DAItemGroupArguments(ip, "OPC.IwSCP.1", "!BSTR," + OPC_device_name + ",System.HardwareDescription", 1000, null));
            dAItemGroupArguments.Add(new DAItemGroupArguments(ip, "OPC.IwSCP.1", "!BSTR," + OPC_device_name + ",Plc.FirmwareVersion", 1000, null));
            // adding some other items
            using (client = new EasyDAClient())
            {
                client.ItemChanged += client_Main1_ItemChanged;
                client.WaitForMultipleItemValues(dAItemGroupArguments.ToArray());          
                Thread.Sleep(10 * 1000);              
            }
        }
 public void client_Main1_ItemChanged(object sender, EasyDAItemChangedEventArgs e)
 {
       if(e.Succeeded==true)
       {
           item_value = e.Vtq.ToString();
           Console.WriteLine(item_value);
       }