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LSL / USL

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Viewing 9 posts - 1 through 9 (of 9 total)
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  • November 19, 2001 at 8:04 pm #28247

    A.H.
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    Are the specification limits set by targets by yourself or customers?

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    November 19, 2001 at 8:30 pm #70045

    Sinnicks
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    Participant

    In manufacturing organizations, control specs are usually calculated from a relatively large sample size (n=40) with two measurements taken per subgroup, assuming a stable process.  The purpose of control charting is to monitor the “health” of the process.  This site has a good section on control charting.
    The measurement system itself though, should incorporate both effectiveness and efficiency metrics.  The effectiveness measurements (eg….defects per unit) are for process points that frequently touch the customer experience. These specs (usually just one upper or lower) are determined by the customer.  Efficiency measurements on the other hand, measure the minimization of waste in pursuit of effectiveness (eg…percent value-added time), and specs (again, just an upper or lower) should be determined by the person most knowledgable about the process. 

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    November 20, 2001 at 1:20 pm #70059

    Jaran S.
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    If customer set clearly specification, then I use LSL/USL by customer.
    However, we often have no specification from customer. Customer may not define the specification clearly or it is just an internal process with no specification. In this case I will set the specification myself using information, data I have or using expectation from other department (internal customer).
    Jaran S.

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    November 20, 2001 at 2:18 pm #70063

    Ravi Khare
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    Participant

    Specification Limits are always set by customers …. whether ‘internal customers’ or ‘external customers’.
    Specifications set by internal customers ; very often by downstream processes on upstream processes; are based on the tolerable input variation from upstream processes (…noise) to enable the downstream process to deliver well within it’s own spec limits.
    Ravi
    http://www.symphonytech.com
     

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    November 20, 2001 at 7:12 pm #70073

    Ken K.
    ★★★★★★★★★★
    Participant

    Both.
    Sometimes we get specs from customer. Someties we don’t, so we determine them ourselves. Sometimes we create specs more stringent that the customer’s and use those instead of the customer’s.

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    November 21, 2001 at 10:21 am #70088

    Sridhar
    ★★★★★★★★★★
    Member

    Hi
           Specification Limits are set by the customers only. We will set our Control limits so that finally we achive the customer specifications limits. Control limits comes from the natural vaiation within the process. Always control limits are less than or equal to specifications limits.
    bye
     

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    November 21, 2001 at 1:34 pm #70091

    Ravi Khare
    ★★★★★★★★★★
    Participant

    Control Limits need not be always tighter or equal to the specification Limits. If you have a process whose variation is much wider than the spec Limits ( and in the bargain has a low Cp & Cpk) the Control Limits which will follow the processes natural variation will go wider than the specification limis.

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    November 22, 2001 at 3:40 am #70108

    Sridhar
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    Member

    Hi ravi,
            You are right. But what i mean to say that. You should take care that your control limits should always be less than or equal to Specificaiton limts to assure that your process is within control.
     
    sridhar
    ————–

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    November 23, 2001 at 10:08 pm #70151

    Mike Carnell
    ★★★★★★★★★★
    Participant

    I felt I was experiencing a personal renaissance when on of the Minitab guy’s complimented me on my restraint in my answers. Jeff, I am sorry but I am about to blow it. 
    First you asked about Specification Limits ie. LSL = lower specification limit and USL = upper specification limit. These are not control limits so those of you who can’t distinguish between the two stop answering questions until you pass SPC 101. You are cyber polluters and you are screwing up the SS world with your ignorance. Stop it.
    Second. You calculate control limits. You do not set them. If you screwed up one and two. Please get out of the business, now.
    Third level of ignorance. Customers always set the specifications. I am sure you have purchased a car or a cumputer or something recently or you probably will around this time of year. I purchased this Sony Vaio computer (my third – they are great and Sony even did their deployment with one of my competitiors) and I have never specified a single parameter to Sony. If you think the Pentiums are specified by customers you are dreaming. The answer to the question is both.
    If you are guilty of 1, 2, & 3 it is time for you turn yourself in for electro shock therapy. It can only help.
    If you are in a participative situation there is a technique called realistic tolerancing. This probably the most enlightened approach to tolerancing.

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