HRN ISO , Larson nomogram, operating characteristic curve of the acceptance plan, statistical quality control attribute acceptance plans, sampling. Fortunately, Larson has determined a nomograph (a graphical calculating Larson’s nomograph can be used as follows: the vertical line on the left-hand side is. From the Larson nomogram, the binomial plan satisfying these specifications is n1⁄, c1⁄ Using the Lieberman and Owen () tables for D1 1⁄(20).
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NPTEL :: Management – Six Sigma
If the process or quality controls have broken down, the sampling procedures will prevent defective products from going any farther. The part is classified as good or defective. R is computed and marked with an arrow as shown on the diagram. The AOQL is the outgoing quality level at the crest of the curve. The sample size is determined as follows: When inspection is performed by attributes, product is classified as good or defective four types of acceptance sampling plans may be used, with lot by lot single sampling plans being the most popular.
If a second sample is inspected: The letter p is the incoming quality level AIQ and P a is the probability of acceptance. The product nomogrqmm be grouped into lots or may be single pieces from a continuous operation. Nomographs were popular before there were computers.
Using the Poisson to calculate probabilities associated with various sampling plans is relatively simple because the Poisson tables can be used. The following other wikis use this file: A periodic audit to verify that conditions have not changed is a recommended practice when products are not checked on a routine basis.
The abscissa on the Thorndike chart is np. Draw a line from the AQL. Random spot-checking may sometimes be used when a process is in statistical control. Both the sample size and acceptance numbers must be integers. It may also be used to approximate binomial probabilities and compute the probability of acceptance for fraction defective sampling plans. Also a straight line can be dropped from R to the pn scale.
The binomial assumes that the probabilities associated with all samples are equal. Although the hypergeometric may be used when the lot sizes are small, the binomial and Poisson are by far the most popular distributions to use when constructing sampling plans.
For this example, the differences increase slightly as the curve approaches the tail. In addition, one hundred percent checking cannot be used when a destructive test is made. Summary [ edit ] Description Larson. The Poisson formula,is used to compute the probabilities of acceptance.
The L may be modified for any value of b. They are also included in various textbooks. Find the closest sample size and acceptance number to the intersection point.
These distributions were covered in the Basic Probability chapter and are reviewed nomograkm. If the process has been controlled satisfactorily, the product would be accepted and passed on to the next organization or customer. For this example, the lot size is pieces. A first sample of size n 1 is taken. The first is the frequency of checking f and the second is the clearing number i.
The problem with this method is that the sample taken from small lots may be too small and the sample taken from large lots may be too large. Two parameters are specified in a continuous sampling plan.
The value of pn is 8. The semi vertical lines on the nomograph represent the sample sizes and the semi horizontal lines are the acceptance numbers. It is represented by the symbol P a. Incoming quality is denoted by p. The values for the operating characteristic OC curve are obtained directly from the nomograph. The Inspection organization or end of the line appraisal function has three larzon that will be achieved in part through sampling techniques. The letter n represents the sample size.
To assist in the task, a tool called an L will be nimogramm. This file is ineligible for copyright and therefore in the public domain because it consists entirely of information that is common property and contains no original authorship. The left or vertical side of the L coincides with the probability of acceptance on the Thorndike nomoframm.
The curved lines in the body of the chart represent the cumulative number of occurrences or successes that are of interest. The sampling risks are not known, so this method will not guarantee that the outgoing quality will be at an acceptable level.