diff --git a/Cigarette/PLC/PLCDevice.cpp b/Cigarette/PLC/PLCDevice.cpp
index 661f147..20d95aa 100644
--- a/Cigarette/PLC/PLCDevice.cpp
+++ b/Cigarette/PLC/PLCDevice.cpp
@@ -7,7 +7,7 @@
 
 extern SysConf g_sys_conf;
 
-modbus_t * g_modbus;		//Modbus TCP
+modbus_t * g_modbus = NULL;		//Modbus TCP
 
 bool PLCDevice::init_plc(PLCDevice* PLCptr)
 {
@@ -29,8 +29,11 @@ bool PLCDevice::init_plc(PLCDevice* PLCptr)
 }
 bool PLCDevice::disconnect_plc(void)
 {
-	modbus_close(g_modbus);
-	modbus_free(g_modbus);
+	if(g_modbus)
+	{
+		modbus_close(g_modbus);
+		modbus_free(g_modbus);
+	}
 	return true;
 }
 int PLCDevice::write_bit_2_plc(int addr, int value)