Five-Point Amplitude Estimation of Sinusoidal Signals: With Application to LVDT Signal Conditioning

A simple algorithm for the amplitude estimation of sinusoidal signals is proposed. It is first shown that three well-spaced samples are sufficient to calculate the amplitude of a harmonic signal. However, the three-point estimator is sensitive to deviation of the sampling rate. To deal with errors that were caused by noncoherent sampling, a modified algorithm that uses two more samples is developed. With the five-point algorithm, estimation errors fall below 0.04% for 1% of frequency deviation. As a demonstration of its simplicity, the five-point estimator is applied to the signal conditioning of a linear variable differential transformer (LVDT) using moderate-speed devices. By implementing the proposed algorithm with a low-cost 16-b microcontroller, a digital LVDT signal conditioner is built and tested with satisfactory performance.