Image Processing Reference
In-Depth Information
Anotherchallengeisthatthedomainishighlycostsensitive.Also,systemshavetobelong-lived,
as they are expected to operate over a significant part of the building life cycle. hey are required to
be “future proof,” which favors proven, technologically conservative approaches. Hence, the domain
is very slow to accept and adopt new technological developments. Bid invitations often require sys-
tems to adhere to international standards, which lengthens the innovation cycle due to the delays
inherent to such standardization procedures. Finally, ease-of-use is of significant importance, both
for operators and occupants.
29.4 Application Modeling
In the world of process and BAS in particular,
data points
(or simply
points
)areaverycommon
concept. Each data point logically represents a single value from the underlying physical process.
Input data points represent sensor measurements, while output data points map to actuators. In
addition, data points may exist which do not immediately map to a physically observable value,
such as a set point. These are called “soft” or “virtual.” In contrast, those which correspond to an
aspect of the real world (such as a certain room temperature or the state of a switch) are called “hard”
or “physical.”
The overall application is defined as functions over these points. The relevant world standard []
divides these functions into three categories: Input/output (I/O), processing, and management.
I/O functions basically wrap a data point. Thus, they describe the task of actually interacting
with the physical world: acquiring environmental and plant data (analog measurements, digital state
inputs, pulse counting for metering purposes) and controlling parameters of the physical world by
way of building services equipment (switching, setting/positioning).
Processing functions then build upon the I/O functions. Feedback control and control sequences
are executed. hus, these functions describe the required automation function (including higher level
strategies such as night purge). In addition, [] includes functions for building services equipment
maintenance such as monitoring of data point limits or run hours in this category.
Management functions form the third category. hey describe the capability of a system to collect
information for human operators to enable them to analyze and optimize its behavior (e.g., by chang-
ing controller parameters or schedules). This specifically includes the accumulation of historical
data (trend data) at specified rates (or value increments) and the possibility to generate reports and
statistics.
For each category, the system has to display relevant data and allow human interaction where
required. For example, measurements need to be displayed to the occupant and/or the system oper-
ator, and set points need to be shown and modified. User interface elements will differ according to
the type of interaction. As examples, consider manually overriding an output right at the actuator
versus examining trend data.
The data flow through the system can be shown in a function block diagram. Function blocks can
be data sources (in case of an I/O function which represents an input data point) or data sinks (in case
of an I/O function which represents an output data point). hey can also transform data (representing
a processing function, which is immediately associated with a set of processing rules). Figure . also
includes a virtual datapoint, which could represent a controller setpoint, and a block representing a
management function (trending/logging). he blocks that are present and their connections form a
directed graph that defines the overall automation application.
For automatic control, nothing more than the present value of a data point is required: to perform
its task, a controller does not require information about whether the damper it controls resides in the
basement or on the top floor.
However, points are also used as a key abstraction for management purposes. In BMS, they provide
the central means to present information from all connected systems to the operator in a unified way.
