Scale Installation & Calibration Procedures Flashcards

A technician notices that a scale indicator displays a stable zero but drifts upward by 0.5 lb over 30 minutes with no load applied. The most likely cause is:

Answer: Thermal expansion of the scale structure or load cell creep under a pre-load condition

Slow upward zero drift without load is characteristic of structural thermal expansion or load cell creep caused by mechanical stress not fully released after installation.

Which NTEP Certificate of Conformance (CoC) parameter directly determines the minimum verification scale division (e) allowed for a specific scale model?

Answer: The CoC specifies the accuracy class and minimum e value the device may be set to

The NTEP CoC defines the accuracy class and permissible range of verification scale divisions for each approved device.

When performing a linearity test on a scale, test loads are applied at approximately:

Answer: 0%, 25%, 50%, 75%, and 100% of maximum capacity

Linearity tests use multiple intermediate points across the range to detect non-linear errors that would not appear from a two-point (zero and span) check.

A truck scale pit is prone to flooding. Which load cell mounting style best protects load cells from water intrusion damage?

Answer: Above-deck mounting with self-checking load cells and IP68-rated cables

Above-deck (surface-mount) configurations keep load cells above potential water levels, and IP68-rated cables withstand submersion should flooding occur.

The 'return to zero' (RTZ) test for a commercial scale requires that after removing the test load, the indicator must return to within:

Answer: ±0.25 e of the original zero reading

NIST HB44 specifies that after load removal the indicator must return to within ±0.25 e of the pre-test zero for the scale to pass.

When installing a crane scale (hanging scale), the technician must verify that the mounting hook's Safe Working Load (SWL) is:

Answer: At least equal to the scale's maximum capacity plus the weight of any rigging attached

The hook SWL must accommodate the full scale capacity and any slings or shackles attached so total suspended load never exceeds the hook's rating.

During post-installation verification, a legal-for-trade scale fails the sensitivity test. Sensitivity is checked by:

Answer: Adding one verification scale division (e) to a loaded scale and confirming the display changes by at least one division

The sensitivity (minimum load) test verifies the scale responds to an increment of 1 e added to a preloaded condition, confirming resolution meets legal requirements.