Scale Installation & Calibration Procedures Flashcards

A calibration certificate for test weights used on a legal-for-trade scale must trace back to:

Answer: NIST or a NIST-traceable accredited laboratory via an unbroken chain of calibrations

Metrological traceability requires an unbroken chain of calibration comparisons back to national standards maintained by NIST.

Which wiring fault in a 4-wire load cell circuit causes a span error but leaves zero correct?

Answer: Increased resistance in the signal (output) wires only

Added resistance only in the signal wires attenuates the mV output proportionally, reducing span without shifting zero because it affects only loaded readings.

On a 6-wire load cell system (4 signal/excitation + 2 sense wires), the sense wires compensate for:

Answer: Voltage drop in the excitation cable, ensuring the cell receives its rated excitation voltage

Sense wires feed back the actual voltage at the load cell terminals so the indicator can adjust its output to maintain the correct excitation despite cable resistance.

A technician is calibrating a batch weighing system that accumulates multiple ingredient additions. The calibration strategy should include:

Answer: Testing at each typical batch increment as well as at the total batch weight

Batch systems must be accurate at each addition point to avoid cumulative errors, so calibration should verify accuracy at the actual operating load points.

What does 'multi-interval' (also called multi-range) mean on an NTEP-approved scale?

Answer: The scale automatically uses a finer division (smaller e) in lower weight ranges and a coarser division at higher ranges

Multi-interval scales switch to a larger verification division as load increases beyond defined thresholds, allowing high resolution at low loads and wider range at high loads.

When installing a load cell in a shear-beam configuration under a tank leg, which mounting condition causes the most measurement error?

Answer: Mounting surfaces that are not parallel and flat, causing eccentric (off-axis) loading

Shear-beam cells are designed for pure vertical load; non-parallel or uneven mounting surfaces introduce side forces and bending moments that degrade accuracy.

A scale technician completes a calibration and issues a calibration label. Under NIST HB44, which party is responsible for ensuring the scale remains accurate between inspections?

Answer: The owner or operator of the scale

HB44 places ongoing responsibility for scale maintenance and accuracy on the device owner or operator between official inspections.