Fieldbus device general Information

fieldbus devices are field instruments, such as transmitters and valves, with processors that monitor device performance and state. fieldbus devices use a digital, rather than analog, connection to a host system such as the DeltaV system. Function blocks reside in the fieldbus devices and enable the devices to execute control in the field. fieldbus devices notify the control system of standard operating parameters and are self-diagnosing and capable of reporting device problems such as instrument out of calibration to the control system.

Each fieldbus device must have a unique physical device tag and a corresponding network address. The device tag is assigned to the device when it is commissioned and (for most device states), the device retains the tag in its memory when it is disconnected. The device does not retain the tag when the device is made Spare. When the device is made Spare, the tag information is lost. The network address is the current address that the fieldbus is using for the device. fieldbus uses addresses in the range 0-255. Group addresses and DLLs use addresses 0-15, commissioned devices use addresses 20-35, standby devices use addresses 232-247, and offline and spare devices use addresses 248-251.

fieldbus supports four device classes:

• Unknown - the fieldbus device class is not known at this time.

• Basic device - sends and receives messages on the fieldbus but does not control when devices have access to the fieldbus.

• Link Master - controls when devices access the fieldbus and executes the link schedule which synchronizes communications with function block execution on the fieldbus. Link Master devices are capable of taking over as LAS if the Primary Link Master device fails. The backup Link Master must use address 20.

• Bridge - links multiple fieldbus segments. This device class is not currently supported. The DeltaV system supports one backup Link Master on each segment.