CWT Measurement Standards & Accuracy 5 — Questions and Answers
Question 1: What is 'span calibration' on an electronic scale?
- Setting the scale's minimum capacity
- Adjusting the scale's output to correctly indicate a known reference weight at full capacity (Correct answer)
- Zeroing the scale before use
- Programming the scale's tare memory
Correct answer: Adjusting the scale's output to correctly indicate a known reference weight at full capacity
Span calibration adjusts the gain of the scale's signal processing so that a known reference weight produces the correct displayed reading.
Question 2: Which of the following best describes 'measurement uncertainty'?
- The probability that the scale will fail during the measurement
- A quantified range within which the true value of a measurement is expected to lie (Correct answer)
- The difference between the displayed and actual weight
- The error introduced by using worn weights
Correct answer: A quantified range within which the true value of a measurement is expected to lie
Measurement uncertainty expresses the range of values that could reasonably be attributed to a measurand, reflecting all sources of error combined.
Question 3: A technician performs five consecutive weighings of the same 10 lb test weight and gets readings of 10.01, 9.99, 10.02, 10.00, and 10.01 lb. What does this data primarily assess?
- Linearity
- Repeatability (Correct answer)
- Eccentricity
- Hysteresis
Correct answer: Repeatability
Placing the same load multiple times and comparing results measures repeatability, also called reproducibility under the same conditions.
Question 4: Under NIST Handbook 44, a Class III scale with 5,000 divisions (n=5000) is classified based on which parameter?
- The scale's physical size
- The number of scale intervals between zero and maximum capacity (Correct answer)
- The type of load cell used
- The scale's installation location
Correct answer: The number of scale intervals between zero and maximum capacity
NIST HB 44 classifies scales by accuracy class (I–IIII) and the number of scale intervals (n), which equals max capacity divided by the scale interval value.
Question 5: What is the significance of 'Type Evaluation' (or 'type approval') for a commercial weighing device?
- It confirms the device was installed correctly at a specific location
- It certifies that a device design meets regulatory requirements for commercial use (Correct answer)
- It records the serial number of the device for tracking
- It verifies the device's calibration certificate is current
Correct answer: It certifies that a device design meets regulatory requirements for commercial use
Type evaluation confirms that a particular model design conforms to applicable standards, allowing that model to be legally used in commercial trade.
Question 6: Which of the following represents the correct hierarchy from most precise to least precise ASTM weight class?
- Class 7 → Class 4 → Class 1
- Class 1 → Class 4 → Class 7 (Correct answer)
- Class F → Class E → Class M
- Class 4 → Class 1 → Class 7
Correct answer: Class 1 → Class 4 → Class 7
In ASTM classification, Class 1 is the most precise and Class 7 is the least precise; precision decreases as class number increases.
Question 7: A 'dead-weight tester' is most closely associated with which aspect of weighing metrology?
- Testing the tare function of retail scales
- Generating precise reference forces using known masses in a controlled gravity environment (Correct answer)
- Checking the waterproofing of load cells
- Verifying the accuracy of counting scales
Correct answer: Generating precise reference forces using known masses in a controlled gravity environment
A dead-weight tester generates traceable reference forces by applying calibrated masses under controlled gravitational conditions, used for high-accuracy force and pressure calibration.
CWT Measurement Standards & Accuracy 5
What is 'span calibration' on an electronic scale?