A common source of error in precision balance work is thehysteresis of the balance suspension. Generally, the feedbackcontrol cannot maintain zero deflection of the suspension asdeadweights are lifted on and off the balance. Few flexuresuspensions approach perfect linear elasticity, and realistically,inelasticity, creep, or stiction can produce unwanted torquesthat must be counteracted to restore null after any translation.Often, these torques can be measured and compensated forin the final result. In our experience with the clamp-supported crossed-flexure pivots that form the hinges of ourbalance mechanism, hysteresis is a problem that is lessenedwhen the pivot foils are loaded in tension. The feedbackcontrol is also set to aggressively control the balance positionduring transitions, so that excursions from null are less than0.5 µm. This high-gain feedback makes for noisy electricalforce readings, however, and, once the balance stabilizes, thegains are substantially reduced for the actual collection ofelectrical force data

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