Troubleshooting Techniques & Repair Methods Flashcards

A portable floor scale is moved to a new location and immediately begins reading approximately 0.1% low. The most probable cause is:

Answer: A change in local gravitational acceleration requiring re-span calibration

Gravity varies with altitude and latitude; moving a scale to a significantly different elevation or location can require a re-span calibration to compensate.

A technician observes that a multi-cell scale's cornerload error is worst at the cell located farthest from the junction box. The wiring and mechanical installation are correct. What should be checked?

Answer: Resistance matching between the load cell cables — longer cables increase sense line voltage drop

Longer cable runs increase resistance in the sense lines, which can cause that cell's contribution to appear different at the summing point, affecting cornerload balance.

A bench scale is found to have a negative shift (reads low) only when a load is placed in one corner. All other corners read correctly. What is the most likely cause?

Answer: A localized crack or fracture in the scale's flexure element beneath that corner

A single-corner low reading while other positions are correct indicates a mechanical fault such as a crack in the flexure or load-bearing element under that specific corner.

After a power surge, a scale indicator boots but the stored calibration constants appear corrupted. The technician cannot locate the original calibration data. What is the recommended procedure?

Answer: Perform a full re-calibration with certified test weights traceable to NIST

When calibration data is lost, a full re-calibration using NIST-traceable certified test weights is required to restore accuracy and legal-for-trade status.

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.

A technician must verify that a newly repaired trade scale meets Handbook 44 repeatability requirements. What is the minimum number of repeat weighings required at the same test load?

Answer: 3

NIST Handbook 44 specifies a minimum of three repeat weighings at the same test point to evaluate repeatability performance.

A scale technician is diagnosing a scale that displays 'UNDER' when a load is applied and the scale platform descends. What condition does this indicate?

Answer: The load cell wiring polarity is reversed, causing the signal to go negative under load

An 'UNDER' or negative reading when the platform is loaded indicates the load cell signal polarity is reversed, causing the indicator to see a decreasing signal when it should be increasing.