SRC Forum - Message Replies

Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

Original Message:

Posted by: Chandu (chandra_hari@rediffmail.com )
Date posted: Sun Feb 23 6:30:03 US/Eastern 2003
Subject: Cusum charts
Message:
I need some help regarding, How to use CUSUM CHARTS for interpreting and predicting the MTBF, When we have some target MTBF. Please help me..

Reply:

Subject: Cusum Charts
Reply Posted by: bdudley (bdudley@alionscience.com )
Organization: RAC
Date Posted: Tue Feb 25 13:16:31 US/Eastern 2003
Message:
A cusum chart is a type of control chart (cumulative sum control chart). It is used to detect small changes between 0.5-2.5 sigma. For larger shifts, Shewart-type charts are just as good and easier to use. Cusum charts plot the cumulative sum of the deviations between each data point (a sample average) and a reference value, T. Unlike other control charts, one studying a cusum chart will be concerned with the slope of the plotted line, not just the distance between plotted points and the centerline. Critical limits for a cusum chart are not fixed or parallel. And a mask in the shape of a V is usually laid over the chart with the origin over the last plotted point. Previous points covered by the mask indicate the process has shifted. A web site that might want to visit is: http://www.ckit.co.za/Conveyor/papers/Bulk%20Solids%20Handling/Monitoring.html Thank you for calling the Reliability Analysis Center.