Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

14.3.5 Uniform data model
UCA protocol 369
The UCA defines a uniform data model for utility devices and equipment via the device
object modeling concepts. Device object models are UCA’s most powerful tool as a
standard for utility data integration. Figure 14.6 illustrates the resulting UCA device object
modeling concepts using a typical water utility pressure reducing valve (PRV) as an
example.
14.3.6 Logical devices
14.3.7 Bricks
UCA device object modeling describes utility equipment through four levels of abstraction.
The highest level is the logical device. In a SCADA application, each individual site
is usually modeled as a logical device, and the site RTU (or similar IED) implements the
device object models. The site RTU contains a UCA server to provide device object
information to the rest of the utility. In our example, the logical device is the PRV site.
Logical devices are made up of a collection of bricks, which are the second layer of
abstraction in the UCA. Bricks usually represent an individual equipment component
within the site. In our example, the PRV logical device has five bricks: two pressure monitor
bricks, a main PRV valve brick, a motorized pilot valve brick, and a flow monitor
brick.
Note that the bricks in our example are re-usable at many sites throughout a utility. This
is particularly true of the pressure monitor and flow monitor bricks.
14.3.8 Component data classes
Bricks are made up of a collection of component data classes, which reside at the third
level within the UCA object hierarchy. Component data classes define the various types of
information available about a device.
In our example, the pressure monitor brick contains information about the pressure
input, which is the measured pressure signal.
It also contains:
• Statistical information about the input. For example, the daily highest value
and time stamp and the daily lowest value and time stamp
• The pressure monitor contains a group of alarm status flags indicating low
alarm, high alarm, high-high alarm, etc
• Pressure monitors also contain an associated set of alarm setpoints
• Finally, pressure monitors contain standard CASM report control blocks to
regulate when and how the pressure monitor reports information about its
measurement value and alarm status flags