Control system using programmable logic controller (PLC) e.g. for manufacturing line

摘要

The control system has a programmable master logic controller (PLC) and a number of remote slave units (RSU1-RSUn), coupled together via a data communication line. The master logic controller has an emergency data setting device (20), providing control data used when the control data from the master logic controller is not received by the remote slave units, each of the latter having a memory (21) holding the emergency data and a memory (22) holding the normal data received from the master logic controller. A switching signal generator provides a signal for switching to the emergency data when the no normal data is received over a defined duration.