Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

370 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
Component data classes are used over and over in many different types of bricks. They
are in simple terms the processing rules related to particular inputs or outputs.
14.3.9 Data attributes
The component data classes are made up of collections of data attributes, which reside at
the fourth and lowest-level within the UCA object hierarchy. Data attributes represent the
specific, concrete pieces of information provided by UCA devices. Again, the UCA data
attribute definitions are common across all utilities. They define the attribute name and
data format.
In our pressure monitor example, the pressure input (i.e., the MV) has four specific
pieces of information (i.e., data attributes) associated with it. Inputs have an integer
representation of the measured value (in 16-bit integer format) plus a floating point
representation (in 32-bit IEEE single precision format). They also have data quality flags
(16-bit wide bit string), and the measured value time stamp (in a 6-octet time format).
14.3.10 Device object use in actual practice
Do not be alarmed if the preceding description of UCA device objects seems complicated
and confusing.
In most cases end users will simply purchase UCA compliant devices.
System designers and application developers will work mostly at the brick level.
Consider again our example of the PRV sites. The site designers will decide what physical
equipment has to go at a site, and go about their normal process of sizing the equipment
and determining the installation details. In the UCA world, this determines the bricks that
must reside in the site’s logical device. All of the lower level information is standard.
The instrumentation and control engineer would specify instrumentation with the correct
bricks.
14.3.11 Current status
Within the electricity industry in the US UCA is widely accepted by both utilities and
vendors. For example the following is a list of utilities and vendors participating in the
UCA effort.