In this case, we use Linux as a data logger as well as an operator interface. Every few minutes, Linux polls the PLC to log system status. The PLC itself keeps a log of significant events in nonvolatile memory in the event of power failures. In addition to the PLC, Linux processes are monitoring other devices, like vacuum gauges, through a multiport serial card. In this application, the interface with the World Wide Web is extremely important.
Scientists travel to synchrotron sources from all over the world to conduct experiments.
When the facility is operational, it runs twenty four hours a day. If our PLC were to shut the equipment down, it is important to be able to diagnose the fault, and if possible, return the equipment to operational status as quickly as possible. By using the World Wide Web, we provide our scientists and engineers with diagnostic tools they can use from anywhere using commonly available interface software. I personally have been able to monitor system status in our PLCs at my desk at work, my apartment in Chicago and a cyber-cafe in London. As we build our instrumentation, we continue to find new applications for this combination.