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A robust Gaussian regression filter and a robust spline filter have been proposed in ISO/TS 16610 to reduce the influence of the deep valleys and high peaks in profiles. However, the differences of the transmission characteristics between the robust Gaussian regression filter and robust spline filter will lead to different evaluation results because of the different calculation methods. It's notable that median process is utilized in both of the robust filters. It shows that the median process is the key point for obtaining robust characteristics. In this paper, a novel two step robust filter is proposed based on the median filter. The calculation process is separated into two steps including the robustness step and the smoothing step. The robustness step is to obtain the robust characteristics of the profile and the smooth step is to eliminate the short-wavelength component of the profile. The experiment showed that an appropriate window length of the median filter will make it possible to not only obtain the robust characteristics but also preserve the long-wavelength components. Spline filter is recommended for the smoothing step because of its advantage of little edge effect. Its effectiveness and application were verified by the experiments.

To solve the problem of inaccurate demodulation resulted from the system uncertain phase shift which exists in the demodulation process of the amplitude modulation (AM) for an inductance displacement sensor, and also to improve the deficiency induced by phase sensitive detection process which would bring in high-frequency noises and decrease the circuit signal to noise ratio, an improved phase sensitive detection process was proposed. The measuring circuit of amplitude modulation inductance displacement sensor was analyzed. One reason of the phase shift occurred in demodulation process was discussed. Meanwhile the principles of the phase sensitive detection and its bringing in the noises were analyzed. Then a symmetric phase-adjustable low pass filter structure was proposed. The AM inductance displacement sensor was prototyped using printed circuit boards and its performance indices were tested. Finally, the experiment results were analyzed. It shows that circuit measuring stability is better than 0.02µm/30min, the maximum measured deviation is 0.09µm within the range of-50µm~50µm. The maximum amplitude deviation approximates 1% when the excitation signal frequency varies in the Center frequency range of ± 5%. Measuring results showed that the symmetric phase-adjustable low pass filter structure can effectively solve the inaccuracy caused by the system uncertainty phase shift and greatly reduce high-frequency noises brought in by the phase sensitive detection process. The proposed inductance sensor meets the requirements of the high precision measurement.

The difficulty of measuring the run-out of engine valve seat related to the centerline of the valve guide is the determination of the datum axis. A method that the gauge was fixed on the conical surface of the valve seat was chosen. One sensor on the conical surface of the gauge measured the run-out of the valve seat related to the centerline of the gauge. The sensors of the gauge on the guide rod measured the centerline of the valve guide. A novel mathematic model of measurement is established. The advantage of this method is that the method of least square circle is needn't. So it is more conveniently on some occasion.