Weighing Equipment Operation & Calibration Flashcards
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Read the first 7 Weighing Equipment Operation & Calibration flashcards as text
What is the purpose of a 'span calibration' on a weighing instrument?
Answer: To adjust the sensitivity so the instrument reads correctly at a known non-zero load
Span calibration adjusts the instrument's sensitivity/gain so that it accurately reads a known test weight applied above zero.
Which environmental condition most commonly causes 'thermal drift' errors in load cell-based scales?
Answer: Temperature changes affecting load cell output
Temperature changes alter the electrical resistance and mechanical properties of load cells, causing their output to drift from the calibrated value.
A technician places test weights on a scale and finds the reading is 0.5 lb low at mid-span but accurate at full capacity. This is most likely caused by:
Answer: Non-linearity or a linearity calibration error
A reading that is off at one point but correct at another indicates a linearity error, meaning the instrument's response is not proportional across its range.
What is the recommended practice before performing a calibration on a vehicle scale in cold weather?
Answer: Allow the scale to stabilize at ambient temperature for at least one hour
Allowing the scale to stabilize ensures that thermal gradients within the structure have equalized, providing a stable baseline for accurate calibration.
Under NIST Handbook 44, what is the term for the difference between the actual value applied to a weighing device and the indicated value?
Answer: Error
Error is defined as the indicated value minus the actual value (or vice versa depending on convention) and is the fundamental measurement of instrument accuracy.
When calibrating a floor scale using substitution weighing, what is the main advantage over direct weighing?
Answer: Substitution weighing requires fewer test weights to verify full capacity
Substitution weighing uses a small set of reference weights plus a known substitute load, reducing the total number of calibrated test weights needed to verify full capacity.
A digital weighing indicator displays 'OVERLOAD' even though the applied load is within the scale's rated capacity. The most likely cause is:
Answer: The load cell output exceeds the indicator's input range due to mismatched sensitivity
If the load cell's mV/V output does not match the indicator's expected input range, the indicator may interpret normal loads as overloads.