LVDT demodulator based on amplitude detector

A circuit technique to demodulate a signal from a linear variable differential transducer (LVDT) is introduced in this paper. The proposed LVDT demodulator consists of the frequency doubler and the sample and hold circuit (SHC). The sum of two output signals of the LVDT is used as the reference signal instead of the excitation signal used in the traditional synchronous demodulators. The reference frequency is provided for the frequency doubler obtained by the phase-locked loop (PLL) to generate the control signal for the SHC. The frequency doubler generates the control signal for the SHC to sample the LVDT signal at the peak position. As a result, the output signal from the SHC is accurately achieved and linearly proportional to the moving core of the LVDT. The realization technique determines the LVDT signal at one-fourth period of the excitation signal. Therefore, the response time of the proposed circuit provides in a quarter of the excitation signal. The circuit configuration of the proposed scheme is simple and low cost. Performances of the proposed demodulator confirmed by experimental results are also included.