CST Vehicle Scale Systems & Applications 2 — Questions and Answers
Question 1: What is weigh-in-motion (WIM) technology primarily used for in vehicle weighing applications?
- Weighing stationary vehicles with higher precision than static scales
- Screening or identifying potentially overweight vehicles without requiring them to stop (Correct answer)
- Replacing static truck scales for certified legal-for-trade transactions
- Measuring individual axle loads of parked commercial vehicles
Correct answer: Screening or identifying potentially overweight vehicles without requiring them to stop
WIM systems screen vehicles at highway speeds to flag potentially overweight vehicles for further static inspection; they are generally not approved as standalone legal-for-trade devices.
Question 2: What is the primary operational difference between a portable axle scale and a full-platform truck scale?
- Portable axle scales weigh only individual axles sequentially, while platform scales weigh the entire vehicle simultaneously (Correct answer)
- Portable axle scales are more accurate than full-platform scales
- Platform scales measure gross weight only; axle scales measure payload only
- Portable scales use hydraulic load cells; platform scales use electronic strain gauge cells
Correct answer: Portable axle scales weigh only individual axles sequentially, while platform scales weigh the entire vehicle simultaneously
Portable axle scales measure one axle group at a time and sum the readings, while full-platform (truck) scales capture the entire vehicle weight in a single or multiple drafts simultaneously.
Question 3: When testing a vehicle scale for repeatability, what is the correct procedure per standard weights and measures practice?
- Apply the same test load at least three times and verify that all readings fall within the allowable tolerance (Correct answer)
- Test at five different positions across the scale deck with varying loads
- Apply the maximum capacity load twice and compare the two readings
- Use a calibrated test truck weighed at different times of day
Correct answer: Apply the same test load at least three times and verify that all readings fall within the allowable tolerance
Repeatability testing requires applying an identical test load a minimum of three times to confirm the scale provides consistent readings within tolerance on each application.
Question 4: What is the most common cause of rocking or instability in a vehicle scale deck?
- Overloading the scale beyond its rated capacity
- Improper load cell mounting, unlevel check rods, or uneven foundation support (Correct answer)
- Electronic interference from nearby high-voltage equipment
- Using an indicator that is incompatible with the load cell rating
Correct answer: Improper load cell mounting, unlevel check rods, or uneven foundation support
Deck instability (rocking) is most frequently caused by uneven support at load cell mounting points, improperly adjusted check rods, or differential settlement in the foundation.
Question 5: What is the function of a check rod (restraint rod) on a vehicle scale deck?
- A device that electronically verifies load cell output accuracy
- A mechanical rod that limits horizontal movement of the deck while allowing free vertical deflection for weighing (Correct answer)
- A calibration reference rod used to establish the zero reference point
- A safety lock that prevents the scale from operating when overloaded
Correct answer: A mechanical rod that limits horizontal movement of the deck while allowing free vertical deflection for weighing
Check rods are mechanical restraints that prevent excessive lateral or longitudinal movement of the scale deck while permitting the free vertical movement needed for accurate weight measurement.
Question 6: What is 'zero drift' in a vehicle scale, and what typically causes it?
- A display rounding error in the indicator caused by software limitations
- A gradual shift of the zero reference point caused by temperature changes, load cell fatigue, or foundation settlement (Correct answer)
- A calibration error introduced by using incorrect test weights during the last calibration
- A communication fault caused by damaged signal cables between load cells and the indicator
Correct answer: A gradual shift of the zero reference point caused by temperature changes, load cell fatigue, or foundation settlement
Zero drift is a slow change in the scale's unloaded reference point over time, most commonly caused by temperature fluctuations, load cell creep or fatigue, and long-term foundation settlement.
Question 7: What is 'shift error' (cornerloading error) in a vehicle scale, and how is it detected?
- An error from overloading one end of the deck; detected by maximum capacity test
- Non-uniform weight response across different areas of the deck; detected by a shift test placing test weights at multiple deck positions (Correct answer)
- An error in the corner digit of the indicator display; detected by comparing display segments
- Mechanical binding at the deck corners; detected by visual inspection of the corner mounts
Correct answer: Non-uniform weight response across different areas of the deck; detected by a shift test placing test weights at multiple deck positions
Shift error refers to non-uniform sensitivity across different zones of the scale deck, and is revealed by a shift (section) test in which a known test weight is repositioned to different locations on the deck.
CST Vehicle Scale Systems & Applications 2
What is weigh-in-motion (WIM) technology primarily used for in vehicle weighing applications?