Forum: Reliability & Maintainability Questions and Answers

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Posted by: IC
Date posted: Mon Mar 5 16:07:21 US/Eastern 2007
Subject: Reliability Apportionment
Message:
I am looking for information in relation to apportionment and the techniques used for calculating it. I have calculated the apportionment for a System with 6 sub-systems (Using the Equal Apportionment Technique from MIL-HDBK-338). NOW I am trying to calculate the apportionment for the sub systems with the new information that each sub system has now been "weighted" (i.e sub sys 1 will be responsible for 20% fo all system failures and Sub sys 2 47% etc etc). Can anybody tell me how I will calculate the new reliability apportionment based on the "weighted" factors or let me know of any techniques/equations that I can use.


Thanks for the help.

Replies: (list all replies)
Reliability Apportionment
John Cloarec Tue Mar 6 6:26:38 US/Eastern 2007
Reliability Apportionment
IC Tue Mar 6 6:27:43 US/Eastern 2007
Reliability apportionment with side constraints
Larry George Tue Mar 6 6:28:47 US/Eastern 2007
Allocations
BWD Fri Mar 9 13:18:14 US/Eastern 2007

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Posted by: Rushabh
Date posted: Mon Mar 5 16:06:00 US/Eastern 2007
Subject: How to test Long Term Drift (Electroncis Assembly)
Message:
Let me first explain the electronics product. It is similar to pressure transmitter which measures the product and send the data in digital form. The product is using microcontroller based architecture to filter out data and to process the data.


The product is expected to work for 7 years without significant output parameter drift in performance. Here drift is of major concern because of high accuracy desired out of product. Main concern of drift parameters is the output should not go out of range due to drift in measuring electronics or processing electronics for know inputs. We would like to define a test which would measure/ test long term drift ( approx. 7 years ) for the product in given test time of 1000 hrs. to 2000 hrs. Test time is hypothetical looking for expert advise in this.

To define the test I first looked at semiconductor component level drift test. What I found out is output parameter drift is measure for constant input parameter for typical 1000 hrs and it is projected as drift. Some papers provides a justification on this technique by assuming that chip material stabilize within 1000 hrs so there won’t be major drift expected after 1000 hrs. I believe this method is valid for semiconductor so bit reluctant on applying it to electronics assembly. “ EXPERT SUGGESTION REQUESTED ON APPLICABILITY OF THIS TECHNIQUE TO ELECTRONICS ASSEMBLY”

If anyone can help to identify the standard or industry known technique to measure long term / short term drift of electronics assembly then it would be great. Major Challenges :

1 ) Share any standard/guideline info. to measure long term drift of electronics assembly 2 ) What should be test time in this type of test ? 3 ) What should be input parameter pattern CONSTANT / VARYING ?? 4 ) Is there anyway test time can be squeezed by elevating test temperature ??

Any more inputs required to answer this please revert back.

Thanking You in anticipation, Rushabh

Replies:

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Posted by: Richard
Date posted: Mon Mar 5 16:03:11 US/Eastern 2007
Subject: General Aviation Aircraft - Vibration Profile
Message:
Does anybody know of an information link that would illustrate a vibration profile for a general aviation aircraft (e.g. Cessna/Piper etc.). I am specifically looking for something to show the g and deflection etc. in each of the 3 axes to help with circuit card orientation etc. Thanks in advance.

Replies:
General Aviation Aircraft - Vibration Profile
David Dylis Fri Mar 9 12:55:10 US/Eastern 2007

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Posted by: GRIB
Date posted: Mon Mar 5 16:02:07 US/Eastern 2007
Subject: Conversion factor between OH/FH
Message:
The average flight time for an aircraft is 1.75 hrs. the conversion factor between operating hrs and flight hrs OH/FH is 1.24. According to the above information, shall I multiply each failure rate issued from the NPRD per 1.24 in order to obtain the total failure or the MTBF per Flight hours?

Replies:
Convert flying hour failure rate to operating hour failure rate
Larry George Fri Mar 9 12:58:24 US/Eastern 2007

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Posted by: Sue Hedrick
Date posted: Mon Mar 5 16:01:08 US/Eastern 2007
Subject: Resistor Calculation
Message:
With regard to resistor calculations, how can I determine theta EC. I had thought that it was calculated using (storage temp - max operating temp) / resistor power rating. This gives me huge numbers, greater than 600 deg C / W. What should I be doing?


Thanks, Sue

Replies: (list all replies)
Theta-EC
David Dylis Mon Mar 5 17:47:22 US/Eastern 2007
Resistor Calculation
Sue Hedrick Mon Mar 5 17:48:33 US/Eastern 2007
Resistor Temperature/Temperature Rise
David Dylis Mon Mar 5 17:51:37 US/Eastern 2007

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