# Best way to detect PLC, sensor disconnection **URL:** \ **Category:** General Discussion\ **Created:** [April 15, 2014, 11:48am UTC](https://forum.inductiveautomation.com/t/best-way-to-detect-plc-sensor-disconnection/8310 "2014-04-15T11:48:58Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![lvboque](https://avatars.discourse-cdn.com/v4/letter/l/9f8e36/32.png) [@lvboque](https://forum.inductiveautomation.com/u/lvboque)\ **Post date:** [April 15, 2014, 11:48am UTC](https://forum.inductiveautomation.com/t/best-way-to-detect-plc-sensor-disconnection/8310/1 "2014-04-15T11:48:58Z")
Hello, Is it possible to detect the disconnection of a PLC using the prosys OPC Client and Ignition OPC Server? Is it possible to get callback when the PLC is disconnected? What about sensor? Is it possible to detect a disconnection of a temperature sensor as example? Thanks for your advices, ---
**Author:** ![greg.simpson](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/greg.simpson/32/3135_2.png) [@greg.simpson](https://forum.inductiveautomation.com/u/greg.simpson)\ **Post date:** [April 25, 2014, 5:04pm UTC](https://forum.inductiveautomation.com/t/best-way-to-detect-plc-sensor-disconnection/8310/2 "2014-04-25T17:04:14Z")
The temp sensor I am not sure about. You could potentially look at the quality of the tags you are monitoring. You could then alarm off of that. There is also a diagnostics folder that contains a tag called “Connection State”. You could use this as well. ---
**Author:** ![Dravik](https://avatars.discourse-cdn.com/v4/letter/d/e274bd/32.png) [@Dravik](https://forum.inductiveautomation.com/u/Dravik)\ **Post date:** [April 25, 2014, 8:36pm UTC](https://forum.inductiveautomation.com/t/best-way-to-detect-plc-sensor-disconnection/8310/3 "2014-04-25T20:36:24Z")
If it is 4-20ma, You can alarm when it is below 4ma. Thermocouples usually read max when disconnected, can alarm on that. Depends!