Design considerations for an electrobalance microforce sensor

The design of two microforce sensors using the electrobalance principle and based on commercially available galvanometer units is described in detail. A plausible form for the open-loop frequency response to be expected from optical detection of the position of the meter arm is derived by analyzing the dynamics of a pivoted beam. The Nyquist criterion for stability of the feedback circuit necessary to maintain force balance over a specified range of mechanical loads is considered in the light of ease of manufacture and alignment. With both units, it was relatively easy to achieve zero static compliance and a frequency response of approximately 100 Hz with no resonant behavior. Practical aspects of friction, component variation, measurement noise, and temperature stability are discussed. (C) 1997 American Institute of Physics.