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Why gather information at the local controller?
Why does the logic controller represent the best place to collect performance and
diagnostic information?
The local logic controller provides numerous advantages as a data collection and
performance measurement collection medium when compared to other elements of
a process control system- be it in industrial automation or railroad automation. A
local logic controller is inherently "informed" of practically every action of every
controlled equipment. That is not generally the case in most centralized control (or
dispatch) systems, which generally deal with higher level process actions (like setting
a route). A local controller, in contrast, executes each individual operation and
indication (i.e. switch movement, track circuit occupancy). Accordingly, much of
the information which is useful in assessing and monitoring process performance is
already available in the logic of the local controller and must simply be collected and
organized. In order to accomplish this in a higher organization level of the process
system (for example in a centralized control center) significant logic would have to
be added to the system to equate a process reaction to individual equipment
actions (for example setting a route into a siding to number of switch movements,
etc) which essentially is a duplication of the logic already available in local logic
controllers. It is also theoretically possible to collect such data the controlled
equipment itself, however that requires some logic to be available in the controlled
equipment itself, which is not the case in most railroad
applications.
abstract...give
me some specific
examples of how
I can use such
functionality?
Take for example a simple
system behavior such as
lighting a signal
lamp. The local logic
controller (in this example
an interlocking) is
responsible for
processing the associated
logic and controlling
(lighting) the signal.
Accordingly the controller
"knows" how long and
how often the signal lamp
has been lit and also
recognizes when a lamp
out occurs. Since this
logic is already available
in the local controller it
can be easily collected,
analyzed, and centrally
reported. For example
the average time to lamp
out can be calculated
across a system and this
data can be used to plan
preventative lamp
changes in critical
locations and even
measure lamp
manufacturers' relative
performance. A similar
approach is also possible
for switch machines, track
circuits, and practically
every component with an
interface to a local
controller.
obvious--the data is local and not centralized. Process and performance
information is only useful if it is available to individuals with the knowledge and ability
to understand and use it, preferably in an office environment. For more on how
this data can be made available to a business network and some of the steps that
are being taken in the industrial and process control industry, see Functionality and
Applications, specifically the section on Communications.
An additional advantage of local data collection of data is that no changes need to
be made to central control systems in order to take advantage of this functionality
(the communication of information is achieved completely independently of the
control system) -- and with sufficiently capable local logic controllers no back-office
server systems, etc are required.
