This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “Control Charting Techniques – Statistical Process Control for Short Production Runs – 1”.
1. Which of these is the correct expansion of DNOM?
a) Deviation from Lognormal
b) Derived from normal
c) Deviation from normal
d) Deviation from normality
Explanation: The DNOM in DNOM control chart denote the deviation from normal. This technique is used for the process quality control in the case of short process run or production runs.
2. Which of these is used as a technique for process control for short production runs?
a) Using deviation from nominal to plot the control chart
b) Using the variable value to plot the control chart
c) Using the variable change to plot the control chart
d) Using the variable decrease or increase to plot the chart
Explanation: The short production runs are having very wide applications in modern industries. The statistical process control technique used for the short production runs is generally measuring deviation from nominal value to plot the control chart, instead of the variable control chart.
3. If the Mi is the actual sample measurement, and TA is a nominal value, what will be the DNOM?
a) xi = Mi – 2TA
b) xi = Mi – TA
c) xi = 2TA – Mi
d) xi = TA + Mi
Explanation: The deviation from the normal or nominal value (DNOM) is used for the plotting of DNOM control chart. The deviation from the normal is evaluated as,
xi = Mi – TA.
4. The mean of the variable measured is replaced by the mean of ________ value in the case of the DNOM chart.
a) Normal value
b) Deviation from normal
d) Deviation from normal range
Explanation: The DNOM chart is used for short production runs, which used DNOM or deviation from normal as the xas in the case of x chart. SO the mean of variable measured is replaced by the mean of the DNOM values.
5. If in a manufacturing process, the measurements for a certain dimension for a part are, 50, 51 and 52; where the nominal value of the dimension measured is 50, what will be the DNOM mean?
Explanation: We know that the deviations from nominal are,
xi = Mi – TA
By putting values, we get DNOM’s 0, 1 and 2. The mean DNOM will be 1.0.
6. How many samples are generally taken before calculating the control limits for the DNOM x bar and R charts?
Explanation: We use the DNOM mean for the plot of the x bar and R charts using the deviation from the normal. It is recommended that we should take almost 20 samples before calculating the control limits for DNOM x bar and R chart.
7. Which of these assumptions are made while using the DNOM approach?
a) The process standard deviation is same for all parts
b) The process standard deviation is different for all parts
c) The samples size is variable
d) The sample size is 1
Explanation: DNOM approach is defined as the method to plot control charts by calculating the deviation from the nominal value. While using this approach, it is assumed that, the process standard deviation is same for all parts.
8. Which of these is true for DNOM approach?
a) The sample size is variable
b) The process standard deviation is different for all parts
c) The sample size varies from one part to another
d) The sample size remains same for all parts
Explanation: It is desirable that, the sample sizes, which are used to find out the observations data, should be constant, when the DNOM approach is to be used for the control charting.
9. What is used instead of Nominal values when the nominal value is not given in the case of DNOM approach?
a) Historical process standard deviation
b) New standard deviation
c) Historical process average
d) Historical process variance
Explanation: The DNOM approach is based on using the deviation from normal data instead of the variable itself. When the nominal value is not given for this, the historical process average is used instead of the nominal value.
10. Which of these does not need to have the nominal value specified frequently?
a) When part has two-sided specifications
b) When part has one-sided specifications
c) When the part can’t have one sided specifications
d) When the part has either one-sided or two sided specifications
Explanation: It is generally very obvious that the DNOM approach needs the nominal value quite frequently but, when the part has one-sided specifications, the nominal is not specified frequently.
11. Standard hypothesis testing procedures are used to compare __________ process average to a desired process target to determine whether the process mean is different from the target.
Explanation: The DNOM uses the historical process average data when the nominal is not available. Standard hypothesis test procedures are used to compare this with the process target, to check their difference.
12. Which of these will work correctly and efficiently, when the process standard deviations are different for different part numbers?
a) Standardized x bar and R charts
b) Standardized attribute charts
c) DNOM charts
d) Both, the cusum and EWMA charts
Explanation: While creating the DNOM based x bar and R charts, it’s assumed that the different parts have same standard deviations. When they are not same, the standardized charts are used.
13. Standardized R chart which uses control limits D3 and D4 has the value of \(R_i^s\) = _________
Explanation: The standardized R chart is used when the parts have different standard deviations. It has the quantity plotted as,
14. Deviation from the process target charts work efficiently when the process standard deviation is not same.
Explanation: While constructing the DNOM charts, it’s believed that the process standard deviations are same. But if they are not, they don’t perform well. The same occurs for the Deviation from the Process target charts.
15. Sample size is allowed to vary for the construction of the DNOM based control charts.
Explanation: It is a necessary assumption for the DNOM based x bar and R charts that, the Sample size must be constant for all part numbers. Without this the control charts don’t give effective results.
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