CST Repeatability & Linearity Testing 3 — Questions and Answers
Question 1: What effect does temperature change during a repeatability test have on the results?
- Temperature has no effect on electronic scales
- Temperature changes can introduce thermal drift, invalidating the test (Correct answer)
- Higher temperature always improves repeatability
- Temperature only affects analog scales
Correct answer: Temperature changes can introduce thermal drift, invalidating the test
Thermal drift from temperature changes during testing can mask true repeatability errors or create false failures, so tests should be conducted at stable temperatures.
Question 2: A linearity test uses test weights placed at 0%, 25%, 50%, 75%, and 100% of capacity. Which loading sequence is preferred for detecting hysteresis combined with linearity error?
- Ascending loads only
- Random load order
- Ascending then descending loads (Correct answer)
- Descending loads only
Correct answer: Ascending then descending loads
Testing with both ascending and descending loads reveals both linearity errors and hysteresis, which only appears when comparing loading and unloading paths.
Question 3: On a multi-interval scale (multiple ranges), linearity testing must be performed:
- Only within the first interval
- Within each weighing interval separately (Correct answer)
- Only at the transition point between intervals
- At maximum capacity of the highest interval only
Correct answer: Within each weighing interval separately
Each weighing interval of a multi-interval scale has its own tolerances and must be evaluated independently for linearity compliance.
Question 4: A vehicle scale shows good repeatability at one axle position but poor repeatability when the vehicle is centered on the scale. The most likely cause is:
- An out-of-tolerance indicator
- Uneven load distribution across the deck or load cells (Correct answer)
- Incorrect span calibration
- Insufficient minimum load
Correct answer: Uneven load distribution across the deck or load cells
Poor repeatability that varies with load position on a vehicle scale typically indicates uneven load cell response or deck flexion affecting load distribution.
Question 5: The 'corner load test' on a platform scale is most closely related to which scale performance characteristic?
- Repeatability
- Hysteresis
- Shift (off-center load) error, related to uniformity of response (Correct answer)
- Minimum capacity
Correct answer: Shift (off-center load) error, related to uniformity of response
Corner load testing evaluates shift error — variation in reading based on where a load is placed — which is related to the uniformity of the scale's spatial response.
Question 6: During a linearity test, a technician notices readings are consistently 0.5 scale divisions high across all test points. This most likely indicates:
- A nonlinearity error
- A zero offset error that shifts all readings uniformly (Correct answer)
- An eccentric loading problem
- Poor repeatability
Correct answer: A zero offset error that shifts all readings uniformly
A uniform offset across all test points is characteristic of a zero error, not nonlinearity, since nonlinearity would produce varying deviations.
Question 7: What is the purpose of the 'shift test' performed after a linearity test on a platform scale?
- To verify the scale division value
- To confirm corner-to-corner consistency of load cell response (Correct answer)
- To test the scale's response to shock loading
- To evaluate the display update rate
Correct answer: To confirm corner-to-corner consistency of load cell response
The shift test confirms that load placed at different positions on the platform produces the same reading, ensuring all load cells contribute proportionally.
CST Repeatability & Linearity Testing 3
What effect does temperature change during a repeatability test have on the results?