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ppm Calculation

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  • #29332

    Naim Kapadia
    Participant

    I quick question from the formula below
    Defects x 1000,000 = PPM
    Baseline
     
    where does the baseline comes from?
    An Example
    Out of 150 boards 5 boards are chosen for inspection, no of opportunities 4
    no of defects found 3.
    How is PPM calculated? from above equation
    is opportunty the number of types of defects?

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    #75007

    Thomas T.
    Member

    Naim,
    Calculating your baseline and creating an appropriate sampling plan are two separate issues. You need to ensure that your sampling plan is sound before you calculate your baseline sigma. I’ll explain how to calculate your baseline — maybe someone else can help with the sampling plan.
    Units = 5
    Opportunities Per Unit = 4
    Total Opportunities = 20
    Defects = 3
    Defects Per Million Opportunities = (3/20)*1,000,000 = 150,000
    Process Sigma = 2.54 (using iSixSigma’s Calculator)
    Hope that helps,
    Thomas

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    #75011

    Miguel Camargo
    Participant

    Hi,PPM is used for estimating the failure rate considering each unit as a defect. No mather how many atributes each part failed (ex: One unit failing for wrong color & wrong size means only one defect).PPM (Parts per million)=
    (Defects/Total units inspected)* 1,000,000 =DPMO is used considering each single defect as a reject. The baseline changed depending on how many attributes each part has(Ex.: One unit failing for wrong color & wrong size means 2 defects, each device has two chances per unit).DPMO (Defects per million opportunities)=
    Defects/(Total units inspected*Chances per unit) * 1,000,000 =

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    #75024

    Thomas T.
    Member

    Miguel,I’ve never heard of PPM being different from DPMO before. So it sounds like this is a common definition in your place of work? We would call a unit defective if it had one or more defects found within it. You could then calculate defectives per million opportunities (ah, symantics!).So, if I understand your comment correctly we would need more information from Naim before we could calculate the PPM. He stated that there are 3 defects found, but we don’t know if they’re all on one unit or on 3 separate units.Thanks for your comment.Thomas

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    #75030

    Mike Carnell
    Participant

    Thomas,
    PPM comes in a lot of forms and it isn’t always tied to oportunity counts.
    If you have a copy of Minitab check out the Capability Study information. Across the bottom it is all in terms of PPM and there is no input for oportunities.
    Miguel has provided a very common definition of PPM.
    Just my opinion.

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    #75077

    Miguel Camargo
    Participant

    Hi,The reason for calculating PPM & DPMO by separate depends on the process that you want to monitor. Some books use PPM & DPMO as the same thing, but some others don’t, furthermore just focus on the concept not the names. If there is a rework cost that would be increased due to one single rejected unit has multiple defects then it would be better to use DPMO.For some industries re-work is not appropiate, so that DPMO is useless. BR,Miguel Camargo

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    #75105

    Naim Kapadia
    Participant

    Another example
     
    How can I work out PPM from information below
     
    No of boards inspected = 5
    No of apertures = 1550/board
    No of opportunities = 4
     
    I am sure this may things easier for Thomas & Migual
    please respond
    Defects found = 720 over 5 boards

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    #75115

    Mike Carnell
    Participant

    I am probably going to get hammered on this response but here goes.
    DPMO is a management metric. It carries the complexity factor with it through the op count. It is useful if you have to level the playing field between dissimilar types of things i.e. aircraft engines, light bulbs, and credit card transactions.
    I the situation most BB’s are in they really do not need to complicate their life getting into the fight over what is and what is not an oportunity count. A metric of PPM or DPU will cover the project adaquately and is actually more understandable to people working in the process.

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    #75119

    Joy Cowling
    Participant

    Just in case you get hammered, I’ll back you up first. 
    PPM calculations are very useful within projects.  The complexity of opportunity counting doesn’t make much sense when you are just comparing a process to itself (baseline to goal).
    DPMO is definitely a management metric, and even then it can get very dicey.  I work with a company that has several businesses that manufacture COMPLETELY different types of products.  They have given me several examples of how when the corporate management tries to get them on a level playing field with opportunity counting, it gets very complicated and in some cases doesn’t make much sense.  I think it is very difficult to get everyone in a diverse company to agree to what they will call an opportunity, do it correctly and consistently so it can be used to compare very unlike processes. 
    I also see the value in making it work. I’m not arguing against DPMO, just making the point that it can be very difficult to get it done consistently.  It is one of those “easier said than done” things…which doesn’t mean it isn’t important or valuable. 
    I’m going to stop now.  Let the hammering begin. :)
    Joy

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    #75121

    billybob
    Participant

    I bet to your surprise I have to agree.  We are really begining to look at DPMO in my facility, matter of fact we always reported it on a plant wide basis.  But we  produce single plastic injected pieces to complete assembilies with many components. A bad injected ring carries the same weight as a bad total assembly.
    I am pushing for DMPO by product family as I believe that this will be a better benchmark to show change from.   Its tough not being able to bring my possum farm into the subject but sometimes you just got to conform to the expected norm!

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    #75165

    Manu
    Participant

    I recognize that the DPMO term gets dicey, when it comes to identifying opportunities to compare one company with another.
    But if we are improving an internal process (Baseline to Goal), the DPMO terms makes sure that the team identifies all the possible opportunities in a process, and make improvements. I’ve found it to be an eye opener, when i was doing a payments process improvement. Had i taken PPM inthat case i might have missed some opportunities.
    However if you compare industries, the opportunities word has a different meaning and is a little dicey.i.e if you compare a pin making industry to car industry, it leads to ambiguity in deciding opportunities. My suggestion in that case would be to count opportunities in terms of customer CTQs.
     

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    #75166

    Arun Nair
    Participant

    Naim,
     Clarify please:
    1. is each aperture in your board an opportunity for inspection?
    Since you have mentioned that the no of opportunities is 4, that would imply that the total number of opportunities is 5*4 = 20. We have 720 defects. This doesnt make sense
    If each aperture is an opportunity and the total number of units is 5 then the number of defects being given as 720 works out to  Z=2.805 ( short term) with a PPM of 96000 ( Minitab Product Report)
     

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    #75178

    Dewayne
    Participant

    Correct, or not, I tend to look at PPM and DPMO as two different topics when working with management decisions as to quality.  Eight products failing out of 1MM is the PPM. Each product may have five critical opportunities for failure when DPMO is the consideration, that being a separate issue.
    It matters not whether one opportunity for failure, or four results in the item’s failure. Either condition results in a defective end product.
    Both factors are important, it is just that one term pertains to pass/fail, the other pertains to the degree of quality risk involved to attain the classification of passed.
    In my opinion, Naim, management needs to first define what it wants, with the information furnished addressing that definition. Providing both establishes an even better picture of quality. Improvement goals could then address not only reducing the number of failures, but also the opportunity for failure

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    #75182

    Marc Richardson
    Participant

    OK, here’s my .02 worth.
    PPM is a more customer-focused metric. The customer only cares that the cell phone she buys works. She does not care, in the event that it stops working, that there are 3 reasons it quit.
    DPMO can be abused to make quality levels look better than they really are. An Example: say I build one million cell phones. I have determined that each cell phone has 25 characteristics that I should be monitoring, so, each characteristic represents an opportunity for error. That would give me 25,000,000 opportunities. Now let’s say that in a random sampling of 100 phones, I discover that 5 of them contain a total of 8 nonconformances. In terms of PPM’s I have a n/c rate of 50,000. Using DPMO, the rate is 3200.
    I am not saying DPMO is inherently deceitful. I am saying that it is important to be clear about what metric one is using.
    Marc Richardson

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    #75192

    Gabriel
    Participant

    I am not used to DPMO, but it seems to me that reaching a good sigma level can be as easy as increasing the number of oportunities.
    Imagine an electronic circuit (taken form the “Sigma Calculator up here). The failure is “the board does not function properly”. And the oportunities are a printed board, many resistors, diodes, transistors, capacitos and solder points (any of them that fails and you have a “failure”). Imagine that the component that mostly fails is the printed board. Just add a few resistor, diodes and solder points and your DPMO (and sigma level) will increase dramatilty, even when you deliver the sme PPM of non conforming circuits to your customer.

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    #75209

    Ricardo Perez
    Member

    The only difference for me is,
    PPM is the notation when you are working with a variable CTQ
    DPMO or DPU is  the notation when you are working with an attribute CTQ.
    Does not matter which one you are using, you will transform it to Sigma Level, Z, and then you could compare processes.
    I hope this helps,
     
     

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    #135921

    Bruno
    Participant

    I would like to know what I do to calculate PPM for variable characteristic considereing any distribution as Weibull, Gamma or Exponencial?
    Thank you.

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    #178945

    Harsh nidhi singh
    Participant

    How ppm can be calculated in a company for all its
    basic need and overall ppm.

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    #178946

    Darth
    Participant

    It can’t be calculated for overall. It has no meaning, don’t bother.

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