Control Phase: SPC Flashcards
7 cards from real Lean Six Sigma Black Belt Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Control Phase: SPC flashcards as text
Which of the following best describes the CUSUM chart's advantage over a traditional Shewhart X-bar chart?
Answer: It is more sensitive to small, sustained shifts in the process mean
CUSUM (Cumulative Sum) charts accumulate deviations from the target and are highly sensitive to small sustained shifts that Shewhart charts often miss.
The d2 constant in control chart formulas is used to:
Answer: Estimate the process standard deviation from the average range
d2 is a control chart constant that converts the average range (R-bar) to an estimate of the process standard deviation: σ̂ = R-bar / d2.
A short-run SPC technique is used when:
Answer: Production runs are too short to establish traditional control limits
Short-run SPC methods (e.g., standardized charts, DNOM charts) are designed for job-shop environments where each run produces too few parts for standard control limits.
On an EWMA chart, a smaller smoothing parameter λ (lambda) results in:
Answer: Higher sensitivity to small, gradual process shifts
A smaller λ gives more weight to historical data, making the EWMA chart more sensitive to small, sustained shifts and less reactive to individual outliers.
When a process is described as 'in statistical control,' it means:
Answer: Only common cause variation is present
Statistical control means the process exhibits only common cause (random) variation with no special causes present, not necessarily that all parts are within spec.
Which SPC chart would be selected to monitor the proportion of defective items when subgroup size is constant at n=50?
Answer: np chart
The np chart monitors the number (count) of defectives in a fixed-size subgroup, making it appropriate when n is constant.
A control chart for individual measurements (I-MR chart) uses a moving range of 2 consecutive values. The control limits for the individuals chart use which constant?
Answer: E2
The I chart uses the E2 constant (E2 = 2.66 for n=2 moving range) to calculate control limits: UCL/LCL = X-double-bar ± E2 × MR-bar.