Statistical Process Control Flashcards
7 cards from real CPP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Statistical Process Control flashcards as text
Which of the following best describes the EWMA control chart?
Answer: A chart that gives exponentially more weight to recent observations
The Exponentially Weighted Moving Average (EWMA) chart applies decreasing weights to older data, making it highly sensitive to small, sustained process shifts.
When using a CUSUM chart, the decision interval H is used to:
Answer: Define the threshold at which the chart signals an out-of-control condition
The decision interval H on a CUSUM chart defines the boundary; when the cumulative sum exceeds H, the chart signals a process shift.
A process engineer notices a sawtooth pattern on an X-bar chart. What is the most likely cause?
Answer: Two distinct process streams being mixed in subgroups
A sawtooth pattern often indicates that samples from two different streams (machines, shifts, operators) are being combined into subgroups, inflating within-subgroup variation.
For an Individuals (I) and Moving Range (MR) chart, what is the typical moving range span used?
Answer: n = 2 consecutive values
The standard MR chart uses a span of 2 (the range between each consecutive pair of individual values) to estimate short-term process variability.
What is the Average Run Length (ARL) used to evaluate in control charts?
Answer: The average number of samples taken before a signal occurs
ARL measures how many samples on average are plotted before the chart signals, used to compare chart sensitivity and false alarm rates.
In SPC, measurement system analysis (MSA) is performed before implementing control charts primarily to:
Answer: Ensure the gauge variation is not masking true process variation
MSA (Gauge R&R) verifies that the measurement system contributes minimal variation compared to the process, ensuring that control charts reflect true process behavior.
Which scenario justifies recalculating control limits on an existing control chart?
Answer: A confirmed special cause has been permanently eliminated
Control limits should be recalculated when a special cause has been identified and permanently removed, so the limits reflect the improved, stable process.