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An alternating current (AC) driven strain gage bridge amplifier system is developed for torque measurement in a brushless motor test bench. AC excitation of the strain gage bridge is applied instead of commonly used DC voltage, and an AC-signal conditioning dual-phase lock-in amplifier is developed using AD630 balanced modulator-demodulator for synchronous detection together with three-pole active Butterworth filter. Thus, lower levels of excitation voltage and lower self-heating of the strain gages are achieved allowing for measurements in very low ranges with high resolution (of about 0.1microstrain/0.05μV/V). The measurement system is controlled in a LabVIEW programming environment through high resolution data acquisition (DAQ) system. Additionally, in the test bench the angular velocity of the mechanical shaft and electrical power data are measured. So the mechanical power data can be compared in real time with the energy consumption and other significant variables. Using this "Power Efficiency" information a number of optimization problems can be solved. [ABSTRACT FROM AUTHOR]