Mixed Deck — All CST Topics Flashcards

Electromagnetic compatibility (EMC) shielding on a digital scale cable is important primarily because:

Answer: It protects the low-level mV load cell signal from radio frequency and electromagnetic interference

Load cell output signals are very small (in the millivolt range), making them highly susceptible to RFI/EMI noise that shielding helps block.

NIST HB 44 requires that the 'test weights' used for field inspection of commercial scales must:

Answer: Be certified to a tolerance within one-third of the applicable device tolerance

Field standards (test weights) used in official inspections must have errors no greater than one-third of the tolerance of the device being tested, per HB 44 requirements.

What is the federal maximum gross vehicle weight (GVW) limit for vehicles operating on U.S. interstate highways?

Answer: 80,000 lbs

Federal law limits gross vehicle weight to 80,000 lbs on interstate highways under the Federal Bridge Formula.

What mechanical feature protects load cells from permanent damage caused by sudden shock loading or overload impacts?

Answer: Mechanical overload stops or bumpers that limit platform travel and deflection

Mechanical overload stops physically limit how far the scale platform can deflect under load, preventing the load cells from experiencing forces beyond their safe overload rating.

An automatic bulk weighing system fills bags of grain sold by weight. Which NIST HB 44 section and key accuracy consideration applies?

Answer: Section 2.22 – Automatic Weighing Systems; batch accuracy over multiple consecutive weighments

Automatic bulk weighing systems are covered under NIST HB 44 Section 2.22, which specifies accuracy requirements evaluated across multiple consecutive automatic weighments.

When replacing a sealed load cell, a technician must apply sealant around the cable entry point. What is the primary purpose of this step?

Answer: To prevent moisture from wicking into the load cell along the cable

Sealing the cable entry prevents moisture from entering the load cell via capillary action along the cable, which would degrade insulation resistance and cause signal errors.

Which part supplies power to the scale’s electronics?

Answer: Power supply

The power supply is responsible for converting incoming electrical current (AC or DC) into the stable voltage and current levels required to operate the scale's internal electronic components. This ensures consistent and reliable operation of the load cells, display, and processing unit.

State weights and measures laws typically define 'short weight' as a situation where the actual quantity delivered is:

Answer: Less than the quantity represented on the label or stated in the transaction

Short weight occurs when a customer receives less product by weight than was advertised, labeled, or agreed upon in the transaction.

What indicates a possible load cell malfunction?

Answer: Erratic or unstable readings

A malfunctioning load cell may not convert force into an electrical signal consistently or accurately, leading to fluctuating or unpredictable weight displays. This instability is a strong indicator that the load cell itself is faulty and requires attention.

Which environmental condition documented during a PM could explain a scale consistently reading high in summer and low in winter?

Answer: Thermal expansion and contraction of the weighbridge structure affecting load cell preload

Thermal expansion and contraction of a scale's structural frame can change the mechanical preload on load cells, shifting calibration seasonally.

What is 'minimum dead load' (MDL) in the context of scale testing?

Answer: The smallest load required before the scale begins to respond

Minimum dead load (also called minimum load or Min) is the smallest load for which the scale's weighing result is considered metrologically acceptable.

What class of weights is typically required for testing Class III commercial retail scales?

Answer: Class F (Field Standard)

NIST Handbook 105-1 specifies that Class F field standard weights are appropriate for testing Class III commercial devices in the field.

In the context of weights & measures certification, what role does continuous professional development play for CST practitioners?

Answer: It ensures practitioners remain current with evolving standards, technologies, and best practices

Continuous professional development is essential in weights & measures certification because it ensures CST practitioners remain current with evolving standards, technologies, and best practices, maintaining competency throughout their careers.

When wiring multiple load cells in a parallel junction box, what must be matched between cells to ensure accurate summing?

Answer: Input impedance of each load cell

Matching input impedance ensures equal current distribution across parallel-connected load cells for accurate summing.

When must a scale technician apply a 'Notice of Non-Compliance' rather than immediately rejecting a device?

Answer: When the violation is administrative (e.g., missing marking) and does not affect measurement accuracy

Non-compliance notices are used for administrative or marking deficiencies that don't immediately impact measurement accuracy, giving the owner time to correct without device rejection.

A hopper scale used in a batching system consistently under-delivers material by a fixed weight per batch. The static accuracy is verified correct. What is the most likely cause?

Answer: Material in flight (inflight material not yet settled on the scale at the cutoff point)

In batching applications, material in flight — falling after the feed cutoff but before it lands on the scale — causes consistent under-delivery that requires an inflight compensation adjustment.

An indicator's internal reference calibration (span calibration) is adjusted using certified test weights. After adjustment, the span error at full capacity is –0.3 divisions. What should the technician do?

Answer: Accept the result if it is within MPE for the device class

A span error within the maximum permissible error for the applicable device class is acceptable and does not require further adjustment.

NIST HB 44 requires that vehicle scales have a minimum division (d) value of no greater than:

Answer: 10 lb

For vehicle scales used in commercial transactions, NIST HB 44 specifies that the value of the scale division (d) shall not exceed 20 lb, with 10 lb being the common requirement for accuracy class purposes.

In the context of load cell wiring & troubleshooting, what role does continuous professional development play for CST practitioners?

Answer: It ensures practitioners remain current with evolving standards, technologies, and best practices

Continuous professional development is essential in load cell wiring & troubleshooting because it ensures CST practitioners remain current with evolving standards, technologies, and best practices, maintaining competency throughout their careers.

Which section of NIST HB 44 covers 'Scales' specifically, including retail, vehicle, and crane scales?

Answer: Section 2.20 and its subsections

NIST HB 44 Section 2.20 and its lettered subsections (2.20.1 through 2.20.8) address scales including general code, retail, vehicle, livestock, and crane scales.