CWT Weighing System Installation & Verification 2 — Questions and Answers
Question 1: What does a 'shift test' or 'corner loading test' evaluate on a platform scale?
- The maximum safe capacity at the geometric center of the platform
- The uniformity of weight indication when a test load is placed at different positions on the platform (Correct answer)
- The zero-return performance after the heaviest load is removed
- The linearity of the indicator over the full weighing range
Correct answer: The uniformity of weight indication when a test load is placed at different positions on the platform
A shift test places a known test load at multiple positions (typically 4 corners and center) to verify the scale reads within tolerance regardless of load placement.
Question 2: During official scale verification, what is the significance of the 'tolerance' value assigned to a weighing device?
- The maximum permissible error the scale may exhibit and still pass verification (Correct answer)
- The minimum test weight mass required to perform the test
- The maximum time allowed for the reading to stabilize after loading
- The maximum rated capacity the scale may be used for commercially
Correct answer: The maximum permissible error the scale may exhibit and still pass verification
Tolerance defines the maximum permissible error (MPE) at any test point; if any error exceeds this value, the device fails verification and must be adjusted or repaired.
Question 3: What qualification must test weights used for official scale verification possess?
- They must be manufactured by the scale manufacturer
- They must be calibrated and traceable to NIST with documented uncertainty (Correct answer)
- They must equal the full capacity of the scale being tested
- They must be stainless steel and stamped with the current year
Correct answer: They must be calibrated and traceable to NIST with documented uncertainty
Verification test weights must have documented calibration with an unbroken chain of traceability to NIST so their true value and measurement uncertainty are known.
Question 4: What does NTEP (National Type Evaluation Program) approval indicate for a commercial weighing device?
- The device has been certified for use in nuclear or radiation environments
- The device design has been evaluated and found suitable for commercial weighing applications in the US (Correct answer)
- The device passed noise and temperature exposure protocol testing only
- The device is approved for export to all foreign countries
Correct answer: The device design has been evaluated and found suitable for commercial weighing applications in the US
NTEP is administered by NCWM and certifies that a device type meets NIST Handbook 44 requirements for accuracy and performance in commercial (trade) applications.
Question 5: What does a 'repeatability test' verify during scale verification?
- That the scale displays a different value on each successive weighing of the same load
- That the scale consistently returns the same reading when the same load is applied multiple times (Correct answer)
- That the scale can weigh multiple items simultaneously without interference
- That the zero display resets automatically between successive weighings
Correct answer: That the scale consistently returns the same reading when the same load is applied multiple times
Repeatability testing applies the same test load multiple times (typically three or more) and checks that all readings fall within the maximum permissible error, confirming consistent performance.
Question 6: How many test positions are typically used when performing a shift (section) test on a rectangular platform scale?
- 2 positions — front and rear thirds only
- 3 positions — left edge, center, and right edge
- 5 positions — four quadrant centers and the geometric center (Correct answer)
- 8 positions — one directly over each load cell
Correct answer: 5 positions — four quadrant centers and the geometric center
NIST Handbook 44 shift test procedures typically place the test load at five positions: near each of the four corners and at the center of the platform.
Question 7: What official action must a weights and measures inspector take after a commercial weighing device successfully passes verification?
- Issue the manufacturer's warranty extension certificate
- Apply an official seal, security tag, or certificate of conformance authorizing commercial use (Correct answer)
- Submit the device for ISO 9001 certification review
- File an OSHA safety compliance report with the state agency
Correct answer: Apply an official seal, security tag, or certificate of conformance authorizing commercial use
After a passing verification, an inspector places an official seal or security tag on adjustment access points and issues a certificate, authorizing the device for commercial trade use.
CWT Weighing System Installation & Verification 2
What does a 'shift test' or 'corner loading test' evaluate on a platform scale?