How is the tolerance range divided in pre-control technique?

Question

BlackTom AI · Accepted Answer

Pre-control divides the tolerance into green, yellow, and red zones.

Relevant knowledge points:
- Tolerance range = Upper Specification Limit (USL) − Lower Specification Limit (LSL).
- Pre-control is a quick, attribute-style control method that color-codes where measurements fall within the tolerance to guide immediate action: green (good), yellow (caution), red (stop/adjust).
- Typical practice partitions the tolerance band into three zones: a central safe zone (green), edge/caution zones (yellow), and the out-of-spec zone (red).

Step-by-step reasoning and example calculation:
1. Compute tolerance. Example: LSL = 90, USL = 110 → tolerance = 110 − 90 = 20.
2. Divide the tolerance into three equal segments to form the zones. One third = 20 / 3 ≈ 6.667.
3. Determine zone boundaries across the range 90–110:
   - Lower third: 90.000 to 96.667 (near the lower edge)
   - Middle third (green zone): 96.667 to 103.333
   - Upper third: 103.333 to 110.000 (near the upper edge)
4. Interpret zones:
   - Green zone (middle third): process running acceptably; continue production if samples fall here (often requires consecutive green samples to be confident).
   - Yellow zones (the two edge thirds inside the specification limits): caution — take closer monitoring, measurement of more samples, or minor adjustments.
   - Red zone (outside the USL or LSL, beyond the tolerance range): stop and implement corrective action (reject parts or adjust the process).

Why the correct answer is correct:
- Pre-control explicitly uses a three-color scheme (green/yellow/red) to partition the tolerance band and prescribe actions; this matches the standard description of the technique.

Why other options are incorrect:
- "Into upper and lower specification limits": those are single boundary values, not a three-zone partition.
- "Into pre-control lines and specification limits": mixes concepts but does not describe the color-zone partition used operationally.
- "Into center, upper, and lower zones": terminology is less precise and omits the standard color coding (green/yellow/red) that defines pre-control practice.

Conclusion: The tolerance range in pre-control is divided into green, yellow, and red zones, which matches the provided answer.

How is the tolerance range divided in pre-control technique?单项选择题

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