We have an application using the CMT-SVR with a Tablet and the operator must hold down a momentary button on the tablet to run the belt. They had an issue the other day where the tablet lost communications with the CMT-SVR and even though the operator was no longer holding the button down, the belt continued to run because it never saw the bit go low. Is there nothing monitoring the connection or communications between the CMT-SVR and the tablet? Seems like it would be nice to have some type of watchdog or something that could be used in the PLC in case comms is lost.
This is a great question! The SVR can identify if a client is connected to the device, but it can take around 30 seconds to detect if a client has disconnected. If the client application is disconnected while a momentary switch is being pressed the SVR cannot identify that a release action has occurred. For applications in which safety is a concern we recommend using a switch mounted to the machine if the connection between the client application and the SVR is unstable.
The other thing I have done is build a “heartbeat” in the SVR that sends the “heartbeat” to the PLC and have the PLC watch it. I have had good success using a Data Transfer (Per-page) Object, using “External Trigger” Mode, Source of a PLW, Destination “Your PLC Data Area”, Trigger “PLB”. Then use a “Set Bit Object” set to toggle that “Trigger” PLB. I have a number other than 0 in the “Source” PLW. Then in the PLC always try to write that “Destination” to 0. So if you have a zero in your "Destination for more than x seconds you know you have lost comms. I have used this method heavily for one of our customers and it seems to work. Make sure you bench test it out. It was some fiddling around to find this combination that seemed to work. Depending on models it may act different but I would test something like this and see what luck you have. We are using Omron CJ2 PLCs and CMT-FHDX220. Let me know if my directions are to hard to understand I can post some screen shots.