CWT Measurement Standards & Accuracy 2 — Questions and Answers
Question 1: What does the term 'traceability' mean in the context of weighing standards?
- The ability to track a scale's location
- An unbroken chain of comparisons linking measurements to national or international standards (Correct answer)
- Recording all weighing transactions in a log
- The process of calibrating a scale on-site
Correct answer: An unbroken chain of comparisons linking measurements to national or international standards
Traceability means an unbroken chain of documented comparisons connecting a measurement back to a recognized national or international standard.
Question 2: Which organization maintains the primary mass standards for the United States?
- ASTM International
- OIML
- NIST (Correct answer)
- NCWM
Correct answer: NIST
NIST (National Institute of Standards and Technology) maintains the primary mass standards for the United States.
Question 3: A scale that consistently reads 0.5 lb high on every load has which type of error?
- Random error
- Systematic error (Correct answer)
- Gross error
- Resolution error
Correct answer: Systematic error
A consistent offset in one direction is a systematic error, often correctable through calibration adjustment.
Question 4: What is the tolerance for an ASTM Class 4 weight used in commercial weighing?
- Tighter than Class 1
- Looser than Class 6
- Looser than Class 1 but tighter than Class 7 (Correct answer)
- Same as OIML E2
Correct answer: Looser than Class 1 but tighter than Class 7
ASTM weight classes are numbered 1 through 7, with Class 1 being most precise; Class 4 falls in the middle range.
Question 5: When performing a linearity test on a scale, what is the technician evaluating?
- Whether the scale reads the same weight repeatedly
- Whether accuracy is consistent across the entire weighing range (Correct answer)
- Whether the scale returns to zero after unloading
- Whether the scale display is easy to read
Correct answer: Whether accuracy is consistent across the entire weighing range
A linearity test checks that the scale maintains acceptable accuracy at multiple points across its full capacity, not just at one load.
Question 6: What is 'minimum capacity' on a weighing instrument?
- The largest load the scale can weigh
- The smallest load that can be weighed within the scale's accuracy class (Correct answer)
- The tare weight of the scale platform
- The weight at which the scale must be recalibrated
Correct answer: The smallest load that can be weighed within the scale's accuracy class
Minimum capacity is the smallest load that can be weighed within the allowable error tolerance for that scale's accuracy class.
Question 7: Which environmental factor most directly causes creep error in load cell-based scales?
- Atmospheric pressure changes
- Temperature changes in the load cell (Correct answer)
- Vibration from nearby equipment
- Humidity affecting the display
Correct answer: Temperature changes in the load cell
Thermal expansion and contraction of load cell materials due to temperature changes is a primary cause of creep and zero drift.
CWT Measurement Standards & Accuracy 2
What does the term 'traceability' mean in the context of weighing standards?