Fieldbus is a digital, bidirectional, multi-branch communication network that connects intelligent field devices and automation systems. It is currently a hot topic in industrial automation. Fieldbus replaces 0-10mA or 4-20mA field electric instrument signals with open, independent, fully digital, bidirectional, multi-variable communication. Fieldbus I/O integrates detection, data processing, and communication, and can replace analog instruments such as transmitters, controllers, and recorders. It does not require frames or cabinets and can be directly installed on field rails. Wiring fieldbus I/O is extremely simple, requiring only a single cable to connect from the host computer to the next fieldbus I/O along the data chain. Using fieldbus can reduce the cost of wiring, installation, commissioning, and maintenance of the control system by about two-thirds. Fieldbus I/O and PLCs can form a low-cost DCS system.
Fieldbus control systems distribute the control station functions of DCS to field control devices, enabling basic automatic control functions to be achieved using only fieldbus devices.
With fieldbus, operators can remotely monitor and adjust parameters of field devices from the central control room, and also predict and locate faults through the self-diagnostic functions of field devices.
By combining a PLC with a fieldbus, a cost-effective and powerful distributed control system can be formed.
PLCs and fieldbuses are inseparable. Fieldbuses themselves are developed by major PLC manufacturers, such as Siemens' PROFIBUS and AS-i.Rockwell Automation's ControlNet and DeviceNet. PLCs from mainstream manufacturers can connect to various major fieldbus networks.
