This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “The Shewhart Control Chart for Individual Measurements”.
1. The Shewhart control charts for sample size n=1 are called ____
a) Single Sample control charts
b) Stationary control charts
c) Control charts for zero variance
d) Control charts for individual measurements
Explanation: The Shewhart control charts for sample size n=1 are called, Control charts for individual measurements. It has no basis of rational sub grouping in this case.
2. In the case of automatic manufacturing, the sample size is ______
d) Greater than 5
Explanation: In the case of automated inspection and measurement technology, every unit manufactured is analyzed and so there is no basis of rational sub grouping. So the sample size here, is 1.
3. In the case of individuals control charts, which of these is used?
a) Relative range
b) Process standard deviation
c) Mean of the highest observations
d) Moving range
Explanation: In the case of individual measurements, we use the moving range of two successive observations as the basis of estimating the process variability.
4. MR (Moving Range) is defined as
a) The difference of highest observation and the lowest observation
b) The difference between any two successive observations
c) The difference between the highest observation and mean of observations
d) The difference between the lowest observation and mean of the observations
Explanation: The difference between any two observations in the data is called the Moving range or MR of the two observations. This helps in estimation of the process variability in the case of the individuals control chart.
Explanation: The UCL for any individuals control chart is given by the following expression,
6. The center line for any individuals control chart represents the value equal to _____
a) The process mean
b) The moving range
c) The mean of moving ranges
d) The process standard deviation
Explanation: The center line of any individuals control chart represents the value equal to x or the process mean for that particular process.
7. The value of ARL for any x bar control chart having 3-σ limits is _____
Explanation: For any shewhart x bar control chart having 3 – sigma limits, we have p=0.0027. The average run length is calculated by formula,
8. The average number of points that must be plotted before an out-of-control point is plotted on an Individuals control chart?
d) Hazard rate
Explanation: The average number of points that must be plotted before a point indicating an out-of-control situation is plotted, is called the Average run length of any control chart.
9. The ARL for any individuals control chart with the 1 sigma limits, and the β=0.972, is ____
Explanation: We know that for any individuals control chart,
Putting the values of β=0.9772, we get ARL=43.96.
10. Which of this stands correct for the relation between the ARL for a shewhart control chart and the individual control chart ARL?
a) ARLindividual control chart=1/ ARLshewhart control chart
b) ARLindividual control chart= ARLshewhart control chart
c) ARLindividual control chart≪ARLshewhart control chart
d) ARLindividual control chart≫ ARLshewhart control chart
Explanation: The Average run length for any individuals control chart with 3 sigma limits is considerably lower than the value of Average run length for any Shewhart control chart.
Explanation: The estimation of the process standard deviation for any individuals control chart is expressed as in the terms of sample standard deviation, s.
14. Moving range can only be calculated by the two successive observations.
Explanation: The moving range is mostly called as MR of span two because it uses 2 successive observations difference for MR calculation. The span can be increased, MR can be calculated by more than 2 observations.
Explanation: The estimation for the process standard deviation is expressed in the terms of the median of the span-two moving ranges by the following expression,
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