Page 25 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes
Example: Automated Car Assembly Plant
An automated car assembly plant is an example of a plant automation system. In an automated
car assembly plant, the work product (partially assembled car) moves on a conveyor belt (see
Fig. 2.4). By the side of the conveyor belt, several workstations are placed. Each workstation
performs some specific work on the work product such as fitting engine, fitting door, fitting
wheel, and spray painting the car, etc. as it moves on the conveyor belt. An empty chassis is
introduced near the first workstation on the conveyor belt.
A fully assembled car comes out after the work product goes past all the workstations. At each
workstation, a sensor senses the arrival of the next partially assembled product. As soon as the
partially assembled product is sensed, the workstation begins to perform its work on the work
product. The time constraint imposed on the workstation computer is that the workstation must
complete its work before the work product moves away to the next workstation. The time
bounds involved here are typically of the order of a few hundreds of milliseconds.

Figure 2.4: Schematic Representation of an Automated Car Assembly Plant

Source: http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Embedded%20
systems/Pdf/Lesson-28.pdf

Example: Supervisory Control and Data Acquisition (SCADA)
SCADA are a category of distributed control systems being used in many industries. A SCADA
system helps monitor and control a large number of distributed events of interest. In SCADA
systems, sensors are scattered at various geographic locations to collect raw data (called events
of interest). These data are then processed and stored in a real-time database. The database
models (or reflects) the current state of the environment. The database is updated frequently to
make it a realistic model of the up-to-date state of the environment. An example of a SCADA
application is an Energy Management System (EMS). An EMS helps to carry out load balancing
in an electrical energy distribution network. The EMS senses the energy consumption at the
distribution points and computes the load across different phases of power supply. It also helps
dynamically balance the load. Another example of a SCADA system is a system that monitors
and controls traffic in a computer network. Depending on the sensed load in different segments
of the network, the SCADA system makes the router change its traffic routing policy dynamically.
The time constraint in such a SCADA application is that the sensors must sense the system state
at regular intervals (say every few milliseconds) and the same must be processed before the next
state is sensed.

Task Organize a debate on the topic “SCADA application is an Energy Management
System”.

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