Field-Based Process Control; Device Description - Endress+Hauser PROline Prosonic Flow 93 FOUNDATION Fieldbus Operating Instructions Manual

5 Operation
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5.3.6

Field-based process control

With the FOUNDATION Fieldbus, field devices can carry out process control functions
themselves, thereby relieving pressure on the higher-level process control system.
Here the Link Active Scheduler (LAS) coordinates the data exchange (between a sensor
and a control valve, for example), and makes sure that two field devices do not access
the bus at the same time.
To do this, configuration software such as the NI-FBUS Configurator from National
Instruments is used to connect the various function blocks to the desired control
strategy – generally graphically (see Page 71).
Fig. 48: Example of field-based process control (flow control)
AI = Analog Input function block, PID = PID function block, AO = Analog Output function block
The producer-consumer relationship means that in FF systems the control loop can be closed directly
between the sensor and control valve. The higher-level system only specifies the setpoint value.
5.3.7

Device description

For commissioning, diagnosis, configuration, etc. make sure that process control
systems or higher-level configuration systems can access all device data and that the
operating structure is uniform.
The device-specific information required for this is stored as so-called device
description data in special files (the "Device Description" - DD). This enables the device
data to be interpreted and shown via the configuration programme. The DD is thus a
kind of "device driver".
Predefined standard DDs are available for the basic functions of measuring devices and
these can be ordered from the Fieldbus FOUNDATION.
Extended device descriptions are always required if a manufacturer implements
additional functions and parameters in his measuring device.
On the other hand, a CFF file (CFF = Common File Format) is required for network
configuration in on-line/off-line operation.
PROline Prosonic Flow 93 FOUNDATION Fieldbus
Endress+Hauser