The signals from the Wheatstone bridge of each ring
load cell are amplified by instrumentation amplifiers. The
initial gain value was estimated in terms of the maximum
compression force chosen for the load cell, 500 N during an
experimental procedure when the rings were compressed with
a hydraulic press in series using a pre-calibrated load cell. With
the correct amplification, the corresponding output voltage of
each ring load cell was digitized. This allowed us to exploit
almost all of the dynamic range of the ADC. The voltage
excitation of the Wheatstone bridge is asymmetrical because
the load cells only sense compression, not traction, and the
bridge always has a positive imbalance. As the sphere weighs
itself, the remaining offset must be compensated. The software
subtracts the extra value. This approach permits corrections