Image Processing Reference
In-Depth Information
Analog input
object
Mandatory network
variables
nvoAnalog
SNVT_lev_percent
nv1
Configuration properties
None
FIGURE .
Functional profile for an analog input. (From Pitzek, S. and Elmenreich, W., Configuration and man-
agement of fieldbus systems. In R. Zurawski, ed.,
The Industrial Communication Technology Handbook
.CRCPress,
Boca Raton, . With permission.)
(none in this example). The arrow specifies that this profile outputs a digital representation of an
analog value, whereas the structure of this output is defined with the standardized (in LON) network
variable type
SNVT_lev_percent
(
.% to .% of full scale). In addition, a profile also
specifies other important properties, such as timing information, valid range, update rate, power-up
state, error condition, and behavior (usually as a state diagram).
While the approach for creating profiles is comparable in different protocols, the profiles are not
always interchangeable between the various fieldbuses, although advancements (at least for process
control related fieldbuses) have been made within the IEC [] standard. Block- and class-
based concepts such as function blocks, as they are defined for the Foundation Fieldbus (FF) or the
PROFIBUS DP or component classes in IEEE . [], can be considered as implementations of
thefunctionalproileconcept.
−
22.5.2 Electronic Device Description Language
The EDDL was first used with the HART communication protocol in []. In , EDDL got
extended by integrating the device description languages of HART, PROFIBUS, and FF, resulting in
an approved international standard IEC - []. An additional standard IEC - extends
EDDL by an enhanced user interface, graphical representations, and persistent data storage [].
In , the OLE for process control (OPC) Foundation joined the EDDL Cooperation Team. In
succession, EDDL is used in the open OPC Unified Architecture.
In EDDL, each fieldbus component is represented by an electronic device descriptor (EDD). An
EDD is represented in a text file and is operating system independent. Within the basic control and
database server, an EDDL interpreter reads the EDD files corresponding to the devices present at the
fieldbus system.
While EDD files are tested against various fieldbus protocols by the vendors, there is no standard-
ized test process for assuring that an EDD works with every available EDDL interpreter. Another weak
point of EDDL is that the functionality that can be described with EDDL is limited by the provided
basic functions in the IEC - standard. hus, device functionality that cannot be described by
these functions is oten modeled via additional proprietary plug-ins outside the standard. With field-
bus devices becoming more and more sophisticated, it will become difficult to adequately describe
devices with the current EDDL standard.
