CPT Measurement & Calibration 2 — Questions and Answers
Question 1: A micrometer reads 0.752 inches but the actual dimension is 0.750 inches. This 0.002-inch error is best described as:
- Random error
- Systematic error (Correct answer)
- Gross error
- Precision error
Correct answer: Systematic error
A consistent offset from the true value is a systematic error, often caused by instrument miscalibration or a zero offset.
Question 2: Which of the following best describes 'measurement traceability'?
- The ability to track who performed the measurement
- An unbroken chain of comparisons linking measurements to national or international standards (Correct answer)
- Recording measurement results in a calibration log
- The process of verifying gage repeatability
Correct answer: An unbroken chain of comparisons linking measurements to national or international standards
Traceability means every measurement can be connected through an unbroken calibration chain to a recognized standard such as NIST.
Question 3: When calibrating a pressure gauge, the technician compares it against a deadweight tester. The deadweight tester is serving as the:
- Unit under test
- Reference standard (Correct answer)
- Working standard
- Transfer standard
Correct answer: Reference standard
The deadweight tester provides a known, accurate pressure value against which the gauge being calibrated is compared, making it the reference standard.
Question 4: A dial indicator has a resolution of 0.001 inch. What does resolution mean in this context?
- The maximum load the indicator can handle
- The smallest increment the instrument can display or detect (Correct answer)
- The difference between the highest and lowest readings
- The allowable measurement error
Correct answer: The smallest increment the instrument can display or detect
Resolution is the smallest change in the measured quantity that the instrument can distinguish and display.
Question 5: A Go/No-Go gage is used to check a shaft diameter. The shaft passes the Go end but fails the No-Go end. What does this result indicate?
- The shaft is undersized
- The shaft is oversized
- The shaft is within specification (Correct answer)
- The gage needs recalibration
Correct answer: The shaft is within specification
A part that passes (enters) the Go gage and does not pass (enter) the No-Go gage is within the specified tolerance range.
Question 6: Which environmental factor most commonly causes thermal expansion errors in precision measurement?
- Humidity
- Vibration
- Temperature (Correct answer)
- Air pressure
Correct answer: Temperature
Temperature changes cause materials to expand or contract, directly affecting dimensional measurements; the industry standard reference temperature is 68°F (20°C).
Question 7: A technician records five measurements of the same part: 2.501, 2.500, 2.502, 2.499, 2.500. The average is 2.5004. This instrument demonstrates:
- High accuracy and high precision
- Low accuracy and high precision (Correct answer)
- High accuracy and low precision
- Low accuracy and low precision
Correct answer: Low accuracy and high precision
The readings are tightly clustered (high precision) but the average is slightly above the true value, indicating a small systematic offset (lower accuracy).
CPT Measurement & Calibration 2
A micrometer reads 0.752 inches but the actual dimension is 0.750 inches.
This 0.002-inch error is best described as: