Modern PLC systems use Remote I/O to connect sensors on the plant floor to PLC controllers located in a different location. This remote I/O strategy eliminates the need for long runs of wiring between each sensor on the plant floor and the PLC, which may be located a hundred feet away.
Using Profibus DP and Profibus PA, the engineer can design a system that uses a single cable to communicate I/O values over a digital bus from I/O cards located near the sensor locations. Interface cards are used at the remote I/O rack to connect the I/O information to the Profibus DP network. Profibus PA can be used to directly obtain data from process sensors and actuators over a separate bus but requires a segment coupler to allow this data to be transmitted to the PLC, which has only Profibus DP ports.
Profinet is another protocol that is popular for communication between PLC hardware and other devices, HMI panels, and Remiote I/O interfaces. Profinet is based on TCP/IP communication and is very different from Profibus DP or PA.
Profibus cables are RS-485 cables with a single pair of single-core wires. Special 9-pin DB shell connectors with terminating resistors are used to connect Profibus DP to a device, such as a PLC. One video of this course will demonstrate how to connect a Profibus cable to the connector, and show how to set the terminating resistor in each connector.