CWT Measurement Standards & Accuracy 3 — Questions and Answers
Question 1: Under NIST Handbook 44, what is the 'acceptance tolerance' compared to the 'maintenance tolerance'?
- Acceptance tolerance is tighter and applies to newly installed scales (Correct answer)
- Maintenance tolerance is tighter and applies to newly installed scales
- Both tolerances are always identical
- Acceptance tolerance applies only to Class III scales
Correct answer: Acceptance tolerance is tighter and applies to newly installed scales
Acceptance tolerances are tighter and apply when a device is first put into service; maintenance tolerances are more lenient for devices already in use.
Question 2: What is the purpose of a 'sensitivity test' on a mechanical beam scale?
- To verify the scale's maximum capacity
- To determine the smallest weight increment that causes a visible change in balance (Correct answer)
- To check for corrosion on the weighing platform
- To test the accuracy of the digital display
Correct answer: To determine the smallest weight increment that causes a visible change in balance
A sensitivity test determines the minimum additional weight that causes a detectable movement of the beam, indicating the scale's resolution.
Question 3: What does 'eccentricity error' (also called 'off-center loading error') measure?
- Error caused by placing the load off-center on the platform (Correct answer)
- Error caused by the scale being installed on an uneven floor
- Drift in the scale's zero point over time
- Inaccuracy at maximum capacity
Correct answer: Error caused by placing the load off-center on the platform
Eccentricity error is the difference in readings when the same load is placed at different positions on the weighing platform.
Question 4: Which OIML class of weights has the most stringent tolerances?
- M3
- F2
- E2
- E1 (Correct answer)
Correct answer: E1
OIML E1 weights have the most stringent tolerances and are used as primary reference standards.
Question 5: A scale displays '±1d' as its division value. If d = 0.01 lb, what is the maximum permissible error for a Class III scale at mid-range?
- 0.01 lb
- 0.5d
- 1.0d
- It depends on the specific load applied (Correct answer)
Correct answer: It depends on the specific load applied
Under NIST Handbook 44, the MPE for Class III scales depends on the number of scale divisions at the applied load, so the specific load must be known.
Question 6: What is the function of a 'check weight' used during a weighing operation?
- To calibrate the scale before each use
- To verify the scale is still reading within tolerance during a production run (Correct answer)
- To set the tare weight of the container
- To test the scale at maximum capacity
Correct answer: To verify the scale is still reading within tolerance during a production run
A check weight is a known reference weight used periodically during production to confirm the scale has not drifted out of tolerance.
Question 7: In gravimetric calibration, what correction must be applied when using mass standards at a location with different gravitational acceleration than where the standards were calibrated?
- Buoyancy correction only
- Gravity correction to account for local g variation (Correct answer)
- Temperature correction to the weights
- No correction is needed since mass is invariant
Correct answer: Gravity correction to account for local g variation
Although mass is invariant, a scale measures force (weight = mg), so local gravitational acceleration differences must be corrected in high-precision work.
CWT Measurement Standards & Accuracy 3
Under NIST Handbook 44, what is the 'acceptance tolerance' compared to the 'maintenance tolerance'?