Strain Gauge & Piezoelectric Sensors Flashcards

What is 'eccentric loading error' (also called side load error) in a load cell, and how is it typically minimized?

Answer: Error from off-center loading; minimized by using rocker pins or universal joints

Eccentric loading introduces bending moments that appear as erroneous force readings; mounting hardware like rocker pins, load buttons, or flexure assemblies redirect forces axially.

According to Handbook 44, what is the maximum permissible error for a Class III commercial scale at or below the transition point (2,000e)?

Answer: ±0.5 division

NIST HB44 allows ±0.5 scale division (e) for Class III scales at loads at or below the transition point of 2,000e.

What does the term 'mV/V' signify when stated in a load cell datasheet?

Answer: The ratio of full-scale output voltage to excitation voltage

mV/V expresses the full-scale output (in millivolts) produced per volt of excitation applied, allowing performance to be stated independent of the actual excitation voltage.

A technician connects a millivolt meter across the signal wires of a load cell under no load and reads a negative voltage when positive is expected. What is the most likely cause?

Answer: The signal wires (+ and −) are swapped at one end

Reversed signal leads invert the differential output polarity, causing the indicator to read negative (or count downward) under normal load.

Which environmental factor most severely degrades the long-term performance of a foil strain gauge load cell installed outdoors?

Answer: Humidity and moisture ingress into the gauge bonding area

Moisture penetrates gauge adhesive and causes corrosion of the foil grid, insulation leakage, and zero drift—the primary long-term outdoor degradation mechanism.

In a tank weighing system with three load cells, the summing junction shows one cell reading 10% higher than the others during a corner test. What is the FIRST corrective action?

Answer: Adjust the trim resistor on the high-reading cell's output to reduce its contribution

A trim (span) resistor is placed in series with the high-reading cell's signal output to attenuate it until all cells contribute equally to the summed reading.

What is the primary advantage of a semiconductor (silicon piezoresistive) strain gauge compared to a metallic foil strain gauge?

Answer: Much higher gauge factor (50–150 vs ~2), enabling greater sensitivity

Silicon piezoresistive gauges have gauge factors of 50–150, providing far greater sensitivity per unit strain than metallic foil gauges, though with higher temperature sensitivity.