Electrical circuitry is useful for thermomechanical analysis apparatus. A sine-type wave force signal is generated by combining a triangular wave with an alternating wave equal in magnitude to about half of the square of the triangular wave. The triangular wave is generated with a control voltage proportional to the operating frequency. A response wave of the apparatus is amplified by an active filter circuit with corner frequencies approximately equal to each other and proportional to the operating frequency to process the wave independently of frequency. The force wave and response wave are converted to square waves which are combined to form pulsed time signals representing a phase difference for each half cycle. A pair of analog switches are receptive of the control voltage and responsive to the respective time signals to feed a switched output to an integrating capacitor such that successive voltage levels are effected in proportion to the time signals and the control voltage. Sample hold modules receptive of the voltage levels effect a steady voltage output representative of average phase shift independently of operating frequency and any time-­varying DC level in the response wave.