Forum: Reliability & Maintainability Questions and Answers

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Posted by: Barry Ma (bma@anritsu.com )
Organization:Anritsu Company
Date posted: Tue May 15 21:33:00 US/Eastern 2001
Subject: PRISM vs. 217
Message:
"It would be more proper to say that PRISM is the successor to the 217", Gary Sunada described when replying a post of "Calculated Failure Rate vs. Field Failure Rate" May 14.
MIL-HDBK-217 has many shortcomings and should be updated. People have been talking about this for years. Now the RAC has presented the PRISM to the Reliability world. Can we have more detailed explanations on the improvements made from 217 to PRISM like "What and how were those shortcomings overcome by PRISM?" For example, one of the critics to 217 is that it is based on component failure data. But the component reliability has been improved a lot over the last three decades. The component failure no longer constitutes a major reason for modern electronic system. Many other failure modes were not incorporated into 217. If this is true, how does PRISM handle the issue? Thank you.

Replies:
PRISM vs. 217
David Dylis Mon May 21 9:37:25 US/Eastern 2001

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Posted by: TY Man (taoyuan_man@yahoo.com )
Date posted: Mon May 14 4:22:00 US/Eastern 2001
Subject: Annual Field return
Message:
There are so many methods out there to calculate the Annual Field Return and also Annualized field return. What is the standard method use by the OEM computer industry?
If I have the field return for a few months, is there a way to predict future returns?

Replies:
Annual Return Rate
Bruce Dudley Thu May 31 15:23:36 US/Eastern 2001

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Posted by: Diane Gordon (info@reliability.com )
Organization:Reliability Center, Inc.
Date posted: Thu May 10 14:06:40 US/Eastern 2001
Subject: Regarding Gearbox Single Reduction Transmission Error
Message:
Answer to a question regarding gearbox single reduction TRANSMISSION ERROR (aka ghost frequency.) What damage can occur to gearbox due to this type of fault?

Replies:
Transmission Error
Robert Arno Fri May 18 12:34:58 US/Eastern 2001

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Posted by: D. Gordon (info@reliability.com )
Organization:Reliability Center, Inc.
Date posted: Thu May 10 13:25:06 US/Eastern 2001
Subject: Calculating Availability for Computer Systems
Message:
I have been searching for information about calculating availability for computer systems. When systems integrators carry out contracts they often have a system availability target of perhaps 99.8%. The people in companies who justify the figures perhaps use different methods of calculation from one company to another.
An example would be an Allen Bradley PLC system with 100 different modules that have quoted MTBFs, the system has some redundancy etc, what is the overall availability. Standards exist (eg bellcore) for calculating reliability of components and cards etc, but when it comes to whole systems there doesn't seem to be any real consistancy and scarce information. Please can you suggest the most comprehensive way of compounding the MTBfs of multipule components to attain an overall availability figure.

Replies: (list all replies)
Availability
Bruce Dudley Tue May 15 9:49:13 US/Eastern 2001
MTTR
Barry Ma Thu May 24 12:56:32 US/Eastern 2001

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Posted by: Steve
Date posted: Thu May 10 10:05:49 US/Eastern 2001
Subject: Calculated Failure Rate vs. Field Failure Rate
Message:
Hello,
I performed a reliability prediction based on TR-332, and the failure rate looks high. We believe that the real failure rate should be better. Since the product is brand-new, no field data available yet. Is there a ratio of calculated failure rate to field one? Or are there any references addressed this issue? BTW, the product is a telecomunication switch used in central office. Thanks in advance! Steve

Replies: (list all replies)
Calculated Failure Rate vs. Field Failure Rate
Gary Sunada Fri May 11 10:47:20 US/Eastern 2001
Calculated Failure Rate vs. Field Failure Rate
Gary Sunada Mon May 14 9:36:54 US/Eastern 2001

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