CWT Weighing Equipment Operation & Calibration 3 — Questions and Answers
Question 1: What does the term 'minimum load' (Min) mean on a legal-for-trade scale?
- The lightest weight the scale can physically support
- The lowest load at which the scale meets its accuracy requirements for commercial use (Correct answer)
- The tare capacity of the scale
- The weight of the empty platform
Correct answer: The lowest load at which the scale meets its accuracy requirements for commercial use
The minimum load is the lowest value at which the scale's indicated error is within the prescribed tolerance for trade use.
Question 2: Which test is specifically used to evaluate a scale's ability to return to zero after a load is removed?
- Shift test
- Return-to-zero test (Correct answer)
- Repeatability test
- Discrimination test
Correct answer: Return-to-zero test
The return-to-zero test verifies that after removing a load the indicator returns to zero (or within tolerance), confirming proper mechanical and electronic reset.
Question 3: A weighmaster is using a counting scale with a reference weight of 100 pieces. If the average piece weight (APW) is entered incorrectly, what is the primary consequence?
- The scale will display an overload error
- All subsequent piece counts will be systematically incorrect (Correct answer)
- The scale will automatically recalibrate
- The tare function will be disabled
Correct answer: All subsequent piece counts will be systematically incorrect
The counting scale derives counts by dividing total weight by the APW, so an incorrect APW causes every count result to be proportionally wrong.
Question 4: Which type of load cell is most commonly used in high-capacity truck scales?
- Pneumatic load cell
- Hydraulic load cell
- Bending beam load cell
- Shear beam or compression load cell (Correct answer)
Correct answer: Shear beam or compression load cell
Shear beam and compression-type load cells are preferred for truck scales because they handle very high loads and are robust against side forces and overloads.
Question 5: When a technician performs a 'shift test' on a floor scale, they are checking for:
- The effect of off-center loading on the indicated weight (Correct answer)
- The accuracy of the tare subtraction feature
- The scale's ability to withstand shock loads
- The temperature coefficient of the load cells
Correct answer: The effect of off-center loading on the indicated weight
A shift (or corner load) test places a test weight at different positions on the platform to verify that off-center placement does not cause unacceptable errors.
Question 6: Under 21 CFR Part 11 requirements for pharmaceutical weighing records, what must be captured in the electronic audit trail?
- Only the final weight reading
- The operator ID, date/time, original and modified entries, and reason for changes (Correct answer)
- The calibration certificate number only
- The ambient temperature at time of weighing
Correct answer: The operator ID, date/time, original and modified entries, and reason for changes
21 CFR Part 11 requires a complete audit trail showing who made each entry, when, what was changed, and why, to ensure data integrity in regulated environments.
Question 7: A technician notices that a bench scale consistently reads 2 grams high regardless of load magnitude. This type of error is called:
- Span error
- Linearity error
- Zero offset error (Correct answer)
- Hysteresis error
Correct answer: Zero offset error
A constant offset that is the same at all load levels is a zero offset (or bias) error, corrected by re-zeroing or adjusting the zero calibration parameter.
CWT Weighing Equipment Operation & Calibration 3
What does the term 'minimum load' (Min) mean on a legal-for-trade scale?