This article presents a design for data acquisition hardware that can automatically track and reject utility frequency components of a measured current or voltage waveform. Measurements of subtle harmonic content in the waveform can therefore be made with the full dynamic range of the on-board analog-to-digital converter. This permits the detection of small, higher frequency signals for applications to condition-based maintenance and energy scorekeeping. Experimental demonstrations in this article show the hardware prototype isolating the rotor slot harmonics in a motor's input current. The high-resolution measurements of slot harmonics permit the estimation of motor speed from the detected slot harmonic frequency and the rejected fundamental frequency. The performance and accuracy of the speed estimator are demonstrated with both steady-state and transient experiments.