Problem/Question(April 17, 2008):

Hello

Some time ago, we got our Omega TEMP/RH circular monitors back from calibration in which most of them were derated +/- 5% Full Scale on the relative humidity monitoring function. Since then, everyone has been assuming that this means that everywhere on the RH scale from 0-100%, there is a +/- 5% inaccuracy. For example: If the RH is 30%, it is being interpreted as a reading anywhere in the range of 25-35%. I believe this to be incorrect as the derating of +/- 5% Full Scale is for 100%. Therefore, a reading, (if I am correct) of 50% RH would have as inaccuracy of +/-2.5%. Further, if there is a RH reading of 25%, then this reading would have an inaccuracy of +/- 1.25%; not +/- 5% as is being assumed now. Is my thinking correct here?

Bill Allison

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Problem/Question(March 3, 2008):

Hello

I need to know what are the mechanical specs for coaxial BNC, RCA and F connectors, because I can't find them in the MIL-STD. What I need is the "cable retention force" of the cable with the connector crmped together.

Thanks very much

Gaby Mourad

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Problem/Question(November 4, 2007):

Hello,

Is there any method to calculate MTBF for Printed Circuit Board?

Regards,

G.vigneshwaran

Reply,November 7, 2007

Hello !

You ask an excellent question ! (MTBF for PC Board). Certainly, the PCB fab does fail, and is an electrical component. However, it is difficult to get statistical field data or test data. (The term "MTBF" is for repairable assemblies; we'll use "MTTF" for a component.).

I have arbitrarily assigned a failure rate to a PCB using a fixed FIT rate (failures in 10E9 hours), ignoring effects of temperature. This at least gets it into the model, but is not based on data. (Recall FIT is the inverse of MTTF).

There is some data in the MIL-217 data base, NPRD95; available from RIAC:
http://quanterion.com/RIAC/index.asp
but it isn't free. Their data is old (1995), and there is not a lot of data for PCB fabs. They do hint that they may come out with an update.

You could model the PCB fab as a set of connectors, but if you use standard SR332 failure rates for connectors, this could result in a unreasonably high failure rate.

I definitely recommend performing a HALT test on the assembled PCB Assembly. I have been successful in identifying PCB fab problems using this test method (problems that only showed up under vibration, and would have resulted in large field return rates.) Refer to: "Improving Product Reliability: Strategies and Implementation" by Levin and Kalal.

So, it's a good question, and I haven't seen much in the way of good answers. If you like, contact me. (Or use a FIT rate of 100 !).

Good luck !

-- John Cooper ASQ CRE, CQE; MSEE

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Problem/Question(October 14, 2007):

Hello,

We are looking for anyone with experience in MSR for a 2 week project. Can you advise of any recruiting agencies that can help find reliability engineers who work freelance?

Regards

Michael Boken

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Problem/Question(December 11, 2006):

Dear All

I am a reliability engineer in the UK and would like to take the ASQ Reliability Engineer Certification. Has anyone completed this examination and got any tips or suggested reading material that they found particularly useful?

Also I wondered if anyone knows of a reliability society which serves the UK well? I am looking to attend conferences and network with others in the field of reliability (&,or medical device reliability) specifically in the UK!

Thanks in advance for your help and suggestions

Sharon McKechnie

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Problem/Question(November 19, 2006):

Hello,

I am working on an assignment for a class in Reliability and Maintainability. The assignment involves doing a reliability assessment for an avionics system. Are there any industry benchmarks for the reliability of avionics systems or components?

Thanks,

Steve Keysor

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Problem/Question(November 12, 2006):

Hi,

I am a enginering student, I am doing a project and I would like send me information about goggle valve. Assembly arrengement, parts, manouvring, actuation, etec

Regards
Oscar Barrios

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Problem/Question(October 25, 2006):

Hello,

I have a question regarding critical power system reliability. The system is simple, an Emergency Diesel Generator feeding into an auto transfer switch. Now my question is if we include a transformer between the same generator and auto transfer switch, and this transformer is properly sized and ventilated, does the overall system reliability drop? Basically, the transformer is more reliable than the generator, and if any one was to fail, the system fails. So in this series system, would the overall system reliability be equal to the most unreliable component in the system?

Regards,

James Couto, EIT

Reply,November 4, 2006

Sorry, reliability = Rsys(t) = P[Life of first part to fail > t] for t >0. If components are independent, the reliability of the system without transformer is

Rgen(t)*Rsw(t)

and with transformer it would be

Rgen(t)*Rtrans(t)*Rsw(t).

The latter is less, even though the reliability of the generator is less than that of the transformer Rgen(t) < Rtrans(t). Unfortunately, parts aren't independent. Transformer efficiency isn't quite 100%, so the generator with transformer has to work harder to make up for transformer heat and other efficiency losses. Furthermore, years from now, the generator may be rebuilt, but the transformer probably won't be, so the ages of the parts will no longer be the same, and the reliability of an old transformer may not be as great as that of the rebuilt generator. The math gets interesting. Let me know if you want more, especially if you are interested in the uncertainty about the reliability of a three-part system compared with a two-part system.

Larry George, www.fieldreliability.com

Reply,November 1, 2006

If this is a series system as you mentioned then theoretically the reliability should drop. Say for example the reliability of the Engine and auto switch are 0.9 and 0.95 respectively then the system reliability would be 0.9X0.95 = 0.855. If you were to include the transformer which has say a reliability of 0.99, then the system reliability would drop to 0.9X0.95X0.99 =0.846.


Omar Thorpe
Reliability Engineer, Product Support

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Problem/Question(October 25, 2006):

Hi,

I am currently employed by an electronics design company responsible for Reliability of product development. I have roughly 18 yrs experience in Electronics and 10 yrs experience in Reliability engineering for product development ! Reliability engineering is not something that could be studied at university earlier on but rather with experience in product development gained through years. I would like to know if you know of any certificate Reliability courses through universities that I can study through correspondence?

Regards
Deven Subramoney

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Problem/Question(July 29, 2006):

Hi,

I am working with field failure data to estimate MTTF and do other prediction. The data we are getting are from Warrant claims made by various customers. We are assuming that those product not come under warranty claims is working. We are using time sensored method. The number of failure reported withn warranty period is around 2%.

But the problem is during modelling and calculation the MTTF value is extremly large and not practical. We are thinking that it may be due to small failure data (2%) we are using.

I will be greatful if you suggest any method or give some references to establish reliability from field failure data.

Regards

Ashok Sarkar

Reply, August 25, 2006

Sometimes it's too much of a strain to estimate MTBF from 2% failures. "Credible Reliability Prediction" combines field data and data from past, similar products, www.asq.org/reliability/pub/ and www.fieldreliability.com/. In that monograph, focus is on useful predictions.

Larry George

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Problem/Question(July 10, 2006):

Hi,

when we have the life of a mechanical part, we should use the weibull function to pridiction of reliability, but i want the slopes(B) of this function for every mechanical part like as "fastener, spring, actuator, gear, ..."


morteza amirizad

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Problem/Question(July 10, 2006):

Hi,

I am looking for a formular that convert the number of hours tested in a high temperature to be equivalent at a room temperature.
Could you help?
Thanks


Vinh Nguyen

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Problem/Question(June 18, 2006):

Hi,

I am a Reliability Engineer intern for Alcoa at Mt.Holly, SC. I am trying to get in touch with someone concerning thermography standards. My project is to assist our Conditioning and Monitoring Team in obtaining an universal standard to distinguish variances of temperature between objects. I know the current training for thermography utilizes the method of detecting problem-areas by comparing the temperature of same objects and picking out the one that has the higher temperature of the group. This presents a problem because all of the compared objects may be defective and choosing the one that has the higher temperature, in some cases, may not be the most reliable method. Hopefully you can direct me to the appropriate person to talk to about this issue, any help would be appreciated!

Thanks!

Jennapher Lingo

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Problem/Question(June 18, 2006):

To Whom It May Concern:

I have a bachelors in Mechanical Engineering (1994) from an ABET accredited university. I’ve spent the majority of my working life in manufacturing as a production supervisor with three years experience in tooling engineering and dimensional control (automotive sector).

What reliability engineering training is available for someone who strongly desires a career path change?

Please advise and thank you in advance.

Regards,

Henri Hammond


Reply, June 19, 2006

Henri: I had a 2 or 3-day seminar called "Reliability Engineering Principles" given by Paul Barringer of Barringer Associates. The seminar gives a very good quantitative methodology for all kinds of reliability issues, no matter your industry. Barringer's website is http://www.barringer1.com/.

Good luck!
Jeff Churchill
Availability Engineer
BP Products North America
440 TSB MC 240
Whiting, Indiana 46394

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Problem/Question(May 22, 2006):

Hi,

Is there any standard derating guidelines available for electronic components used in Telecom applications.
Can some one help please?
Regards
Sriram
HCL technologies

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Problem/Question(April 2, 2006):

Hello:

I am investigating reliability software for use in a chemical plant.

Our primary use would be for a reliability model of our plant, which we would use to assess the reliability of individual units and the overall plant reliability and availability.

I believe the software is referred to RELIABILITY BLOCK DIAGRAM MODELLING

One such software I have found is from Relex
http://www.relex.com/products/rbd.asp

I was wondering who the industry leaders are for such software (i.e. other vendors I should look at)

Also I was wondering what the primary conferences for reliability engineering are
I have found the ISSRE 2006 but was wondering if there are any other big conferences I could attend


Thanks

Reply,December 19, 2006

Item Software, http://www.itemsoft.com/ is one supplier. Advantage Technical Consulting, http://technicalconsulting.advantage-business.co.uk/ is another.

Bryan Tucker

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Problem/Question(April 2, 2006):

Hello:

I work for a small opto-electronics company. I am performing a reliability analysis of a laser radar system. Much of the optical path contains optics that are fiber coupled. The fiber coupled optics contains several fiber optic connectors, one is a standard FC/PC style connector and a second is a custom D38999 style connector. I am having a hard time obtaining any MTBF reliability numbers on these connectors. The manufacturers do not have any MTBF numbers either in a benign or a rugged aerospace environment. Does anyone have any information on how a quantifiable MTBF number can be obtained for fiber optic connectors and/or fiber cable? Are there any industry standards that present any reliability models for fiber optic components? Any information would be helpful. Thanks


Jerry Myers

Program Manager

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Problem/Question(February 25, 2006):

Hello:

I wish to know the guidelines to develp a relaibility policy for a manufacturing industry.


Best regards

Logan Krishnasamy

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Problem/Question(February 25, 2006):

Hello,BR>
Does anyone in your organization have a quick answer for obtaining representative reliability requirements in terms of MTBF for avionics at each appropriate DO-178B level?

* Required reliability of a single-channel ILS receiver at level "A"
* Required reliability of a single-channel VOR receiver at level "B"
* Required reliability of a single-channel VHF Voice Communication Transceiver at level "C"

Thanks for any help.

Tony Robinson, President

Pressing Enterprises, Inc.

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Problem/Question(February 25, 2006):

Sir/Madam

When we have the number of cycles to failure of a part (for example fastener) from it's S-N curve, how can we calculate the failure rate of it?
In the relex software, failure rate calculated easily without the time of using that part.
Thanks
Morteza Khadeni

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Problem/Question(January 20, 2006):

Sir/Madam

I would like some information or sample of calculating reliability of bearing.

Thanks

Morteza Khadeni

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Problem/Question(January 20, 2006):

Sir/Madam

Can you refer me the books on topic related to " Reliability study of Process palnt in design stage"?

With Regards,

A.SURESHBABU
Maintenance Engineering.
SIPS. Chennai-34
TEL NO: 00 91 44 55 84 0320

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