lørdag den 7. februar 2009

The System Definition

The system definition is basically a drawing defining the system at block diagram level. It shows the internal sub systems and important interfaces to neighbouring systems.
At a first glance it seems like a simple document to produce, but once released and posted to interested parties, it can easily cause important discussions.


Let’s take a look at the rough system definition above. The blue line marks the system.

Furthermore, the blue line immediately shows the interfaces. The interfaces are marked with green circles. An interface occurs whenever the system interacts with other systems e.g. the wheels interact with the tracks and the train doors interact with the passengers.

Although the system definition is clear, there are still many issues it would be advantageous and time-saving to discuss as early as possible in the trains life cycle:

- Is the maintenance manual a part of the system?
- Should the system involve coupled trains?
- Should the mission definition be a part of the system?
- Is intentional misuse part of the system?

The system definition can be organized into Generic Product, Generic Application and Specific Application as described in the Safety Approval Process.

The system definition defines the hazards in the hazard log, because hazards occur at the system borders.

Finally, it might end up with a system definition at block diagram level as shown below. The example below shows the sub systems that were considered inside and outside of the electronic brake system of a Copenhagen commuter train type during a safety approval process.
The rectangle boxes are sub systems and the hexagons boxes are measuring sensors.

Please note the system definition is the basis for the hazard log, the safety requirements, the safety approval and other safety activities. Any ambiguity in the system definition will surely cause problems and delays later on in the Safety approval process.

Next chapter >> 3.3 The Safety Plan

Focus on the sources (EN 50129:2003)

See "Quick Guide to Safety Management"

2 kommentarer:

James sagde ...

The block diagram level shows that there are rectangle and hexagon boxes. Is the meaning of rectangle box equal to hexagon box? If not, please kindly explain what does hexagon boxes stands for? Thank you!

Troels Winther sagde ...

Ok - explanation has been added above