Reliability Questions - System vs Component Reliability - Target Values

[jkittle]

Can anyone tell me what the difference is between system and component reliability target vales? I have a new project that is being launched and this is part of my planning requirements.

[Rob Nix]

Originally Posted by jkittle

Can anyone tell me what the difference is between system and component reliability target vales? I have a new project that is being launched and this is part of my planning requirements.

They are at different ends of the reliability spectrum. Component reliability is the reliability of each of the "pieces" of the product, subsystem, and/or system (e.g., a switch, diode, connector, clamp, etc.), and the target is generally the historic reliability (or a little better with improved designs) of past component performance.

System reliability is the composite reliability of all components and/or 'subsystems made up of many components'. The targets established for system reliability are based on calculating all of the 'pieces', whether they are in series or parallel, and other factors. These calculations require some knowledge and background into reliability engineering. I've tried to simplify it as much as possible above. Please tell us a little more about your specific situation.

[Tim Folkerts]

Consider a car engine. Component reliability is how well each part works -- the fuels pump is 99.2% reliable, the spark plugs are 99.996% reliable, etc... System reliabilty is how well the whole system works when put together. System reliability can be improved by such approaches as including parallel components and redundancy.

Tim F

[jkittle]

Tim,

I hate to be so ignorant on this subject but what do you mean by "System reliability can be improved by such approaches as including parallel components and redundancy" What do you mean by parallel components and redundancy? I am not a reliability engineer and not very familiar with any terms associated with reliability. Thanks for your help!

Jerry

[Tim Folkerts]

Parallel means two (or more) items that both perform a particular task at the same time. For example, a truck might have dual tires, so that if one fails, the truck can still operate - perhaps not quite at 100%, but well enough to get by until repairs can be made.

You can also have standby components or systems. For example, an emergency generator for a hospital. This systems only kicks in when there is a failure in the primary system. The space shuttle has - I believe - 5 computers! to manage key tasks. Even if 4 of them fail, the fifth can still handle the task.

Both of these set-ups would be considered redundant, since they are not needed as long as things are working properly.

Tim


P.S. I moved & merged the posts from two other threads. I don't see any forum specifically for reliability, but this seemed like a good choice.

[Rob Nix]

Tim makes good points of which I only alluded to (i.e. series vs. parallel systems). Not to be a killjoy, but like I said earlier, if you do not have some background here, it might be difficult to accomplish your task.

Again, we might be able to help if you give us some details on the specific product you are working on and what you are expected to accomplish.

[jkittle]

The project is the launch of a new entrance door on a school bus.

The old door has premature seal failures and frame failures. The new door takes care of these issues and is cheaper as well.

[Statistical Steven]

Originally Posted by jkittle

The project is the launch of a new entrance door on a school bus.

The old door has premature seal failures and frame failures. The new door takes care of these issues and is cheaper as well.

Component Failure are:

Seals
Hinges
Glass
Material (metal that rusts, plastic that cracks, etc.)

System Failure would be the door fails to work.

An example of a redundant system would be if the door opened electronically, but there was still a manual door open in the event the electronic one did not work.

Does that help?