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Research on Frequency Discrimination of Frequency Modulated Capacitive Displacement Sensor

Author: ChenZuoBo
Tutor: HuangXiangDong
School: Harbin Institute of Technology
Course: Instrument Science and Technology
Keywords: Capacitive sensor Frequency discriminator Micro-displacement
CLC: TP212.1
Type: Master's thesis
Year: 2011
Downloads: 53
Quote: 0
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Abstract


Simple capacitive displacement sensor structure, good dynamic performance, high resolution, to achieve non-contact measurement, detection displacement, flatness, micro-vibration, etc., are widely used in the field of high-precision machining and measurement. FM capacitive displacement sensor commonly used LC oscillator circuit as FM circuits in nanometer displacement measurement weaker FM information, and there is a certain non-linear input-output characteristics. Currently, the use of digital methods developed Kam frequency to achieve high resolution and stability, but often low frequency response, produced with analog frequency discriminator frequency response higher, but the decline in stability and resolution indicators a. Using digital algorithms to correct the nonlinearity of the sensor output, the sensor frequency response will be further reduced. Therefore, in the case of ensuring the sensor resolution, stability and other indicators, the fast discriminator FM signal frequency as well as its input and output characteristics for effective non-linear processing to improve the frequency performance of the key of the capacitive displacement sensor. The frequency discriminator for FM capacitive displacement sensor technology, the subject of in-depth research, the main settlement difficult at the same time to ensure high-resolution and high-frequency response frequency discriminator module, while increasing the frequency discriminator stability, repeatability and other key technical indicators. The main work is as follows: depth study of various types of digital instantaneous frequency measurement method and analog frequency discriminator method, simulation and analysis of its resolution, stability and frequency response indicators, combined with the characteristics of the FM signal, the choice of phase shift product Kam frequency method. The method can achieve the frequency discriminator curve and FM full self-compensating nonlinear curve, traditional methods can not completely compensate for high resolution at the same time have a higher frequency response and stable core device for easy integration multiplier and small size, easy to implement and debug; 2. combined FM signal design downconversion module (including local oscillator circuit based on DDS technology and mixer downconversion circuit), the center frequency of the FM signal is moved around by 3.7MHz 12.5kHz, the FM signal and Kam frequency curve nonlinear self compensation to improve the linearity of the sensor machine output; nonlinear local oscillator signal frequency is greater than the FM signal to self-compensation, to avoid FM signal frequency drift or displacement caused by excessive of similar mirror interference of FM signal frequency is greater than the LO signal occurred, the design frequency of self-correction module, measuring the initial first FM signal, multi-cycle synchronization method of frequency measurement, frequency measurement results corresponding adjustment of the local oscillator signal frequency in order to achieve zero calibration; 4. frequency discriminator module and sensor whole experiment. Static experiments show that the sensor initial spacing of 100μm ± 10μm range to achieve resolution of 5nm, the linearity of 0.835%, one hour indication is stable within 20nm. The dynamic experimental verification sensor with more than 1.1kHz frequency response, dynamic sensor frequency response can theoretically reach 7kHz.

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CLC: > Industrial Technology > Automation technology,computer technology > Automation technology and equipment > Automation components,parts > Transmitter ( converter),the sensor > Physical sensors
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