What type of control chart would be used to monitor the number of defects per unit of output for a process that manufacturers Fibreglass hulls for boats?

Types of variationsAll processes that produce a good or service exhibit a certain amount of “natural” variation in theiroutput. The variations are created by the combined influences of countless minor factors, each one sounimportant that even if it could be identified and eliminated, the decrease in process variability would benegligible.Random variation:natural variation in the output of a process, created by countless minor factorsAssignable variation:non-random variation in process output; a variation whose cause can be identified.Unlike random variation, the main sources of assignable variation can usually be identified andeliminated.The main task in SPC is to distinguish assignable from random variation. Taking a sample of two or moreobservations and calculating a sample statistic such as sample mean makes the task easier. This isbecause random variations are reduced in sample statistics.Sampling and sampling distributionIn statistical process control, periodic samples of process output are taken and sample statistics, such assample means or the number of occurrences of a certain type of outcome, are determined. The samplestatistics can be used to judge randomness of process variations. The sample statistics exhibit variation,just as processes do. The variability of a sample statistic is described by its sampling distribution, whichis the theoretical distribution of the values of the statistic forall possible samples of a given size from theprocess.

The sampling distribution of the sample mean exhibits less variability (it is less spread out) than theprocess distribution. This reflects the averaging that occurs in computing the sample means: high and lowvalues in samples tend to offset each other, resulting in less variability among sample means than amongindividual values. Both distributions have the same mean.Control chartsA control chart in a time-ordered plot of a sample statistic with limits. It is used to distinguish betweenrandom and assignable variation (or equivalently no shift and a shift in the process). It has upper andlower limits, called control limits. They define the range of acceptable variationControl limits:the dividing lines between random and assignable deviations from the mean of thedistribution.Control limits are calculated +/-2 or +/-3 standard deviations of the process mean

Observations from sample distributionsType I error:concluding that a process has shifted (an assignable variation is present) when it has not(only random variation is present)Type II error:concluding that a process has not shifted (only random variation is present) when it has(an assignable variation is present)Determining control chartsThe following steps are usually taken to design control charts:

1.Determine a sample size n (usually between 2 and 20). the choice of n depends on the cost ofinspection versus the expected cost of Type II error. The larger n is, the smaller the probability ofType II error.

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OPMT Ch 10 connectJenna R Tuckanow1.When analyzing an R-chart a plot point is found outside the UCL. What does this indicate

2.Design specification for a motor housing states that it should weigh between 24 and 25 kgs. Theprocess that produces the housing yields a mean of 24.5 kg and a standard deviation of 0.2 kg,

a)What percentage of housing will not meet the design specification?

3.In the MIL-STD-105E sampling plan the inspection level determines the relationship between lot

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