Shaker force measurements using voltage and current

In a previous paper (Smallwood and Coleman, 1993), equations were developed which would allow the force into a test item during a vibration test to be measured using voltage and current measurements from the input to an electrodynamic shaker. To accomplish this, the voltage and current required to drive the shaker with no load and with a known mass were required. In this paper, the equations are generalized to cover the case where the measurements are made with several (at least 2) load conditions. It is not required that one of the conditions be the no load condition. The equations are written in a form where the known loads are not required to be a simple mass, but can be a complex impedance. For the case of more than two load conditions, a least squares solution is found.