diff --git a/SCADA/Program/DataService/PLCGroup.cs b/SCADA/Program/DataService/PLCGroup.cs
index 6d3c26a..67c3ea5 100644
--- a/SCADA/Program/DataService/PLCGroup.cs
+++ b/SCADA/Program/DataService/PLCGroup.cs
@@ -305,7 +305,7 @@ namespace DataService
         object sync = new object();
         protected void timer_Timer(object sender, EventArgs e)
         {
-            if (_isActive)
+            if (_isActive && !_plcReader.IsClosed)
             {
                 lock (sync)
                 {