The local connection between an StrideLinx router and a PLC is usually highly reliable, but if it would be lost certain important features will no longer be working (e.g. remote access over VPN, VNC/HTTP services, Live data, Historical data, and Alarming). You may want to be notified when this connection is lost, in the rare event that it is, so you can take appropriate action.
This article explains several methods to achieve this, combining StrideLinx features with electrical changes in the cabinet or software changes in the PLC:
Power loss check
This method notifies you when the PLC loses power. This only works if the PLC and StrideLinx router are connected to separate power supplies. To also be notified when the StrideLinx router itself loses power, consult the following article: Receive a notification when your device loses connection.
- In the cabinet of the machine, either connect the PLC's power supply or one of the PLC's own digital outputs to the StrideLinx router's Digital Input. The latter is recommended, because if the digital output is false by default and set to true when the program starts, that checks both that the PLC is powered on and that its program is running. Information about electrical wiring can be found in the StrideLinx router installation manual.
- In the StrideLinx Cloud, create a data source for the StrideLinx router's digital input. Follow the instructions in the following article and come back here once you have: Digital Input (GPIO).
- You can now use this signal for different purposes:
- Get notified by e-mail and notification on your mobile phone.
- Follow the steps in the Alarming article, but skip the data source step.
- See the power status live on a device page.
- Follow the steps in the Live data article, but skip the data source step.
- Data visualization tip: use a Live Status component.
- See the historical power status on a device page.
- Follow the steps in the Historical data article, but skip the data source step.
- Tag log condition tip: log the tag "on change".
- Data visualization tip: use a Statusbar or Data Table component.
- Get notified by e-mail and notification on your mobile phone.
Communication check
This method notifies you when the StrideLinx router can no longer communicate with the PLC. This only works if the PLC supports at least one of the protocols supported by the StrideLinx router.
- In the PLC, program a heartbeat signal. A boolean that keeps repeating the cycle of being true for 1 second and then false for 1 second.
- In the StrideLinx Cloud, you can now use this signal for different purposes:
- Get notified by e-mail and notification on your mobile phone.
- Follow the steps in the Alarming article.
- Alarm trigger tip: create two nearly identical alarms. One alarm with trigger condition "true for over a period of 2 seconds" and one with trigger condition "false for over a period of 2 seconds". When communication with the PLC fails, the heartbeat value in the StrideLinx router is no longer updated and it remains either true or false, which then triggers one of the alarms after 2 seconds.
- See the heartbeat signal live on a device page.
- Follow the steps in the Live data article.
- Data visualization tip: use a Live Status component with a single rule to color the background green if the value equals true. When communication with the PLC fails, the heartbeat value in the StrideLinx router is no longer updated and it remains either true or false, which means the component no longer pulses and instead remains solid green or white.
- See the historical heartbeat signal on a device page.
- Follow the steps in the Historical data article.
- Tag log condition tip: log the tag "on change".
- Data visualization tip: use a Statusbar or Data Table component. It is important to note that the Statusbar component will aggregate data if it cannot display all the logged data from the displayed time period on your screen. This effectively means that if too large a period is viewed, the component cannot show each individual heartbeat and it is then recommended to zoom in.
- Get notified by e-mail and notification on your mobile phone.