高精度磁场式时栅传感器激励信号对测量误差的影响分析及系统设计

为提高磁场式时栅传感器测量精度,本文从理论上推导分析了时栅传感器激励信号源幅值和相位不一致产生的谐波成分对时栅传感器测量精度的影响,提出了一种基于DDS原理并采用完整闭环调节的高性能时栅激励信号源设计方案。以FPGA为微处理器,通过编程分频系统时钟,设置频率、相位控制字对DDS输出的信号频率、相位进行调节,使用增益控制器配合相位累加器实现相位到幅值精确转换。搭建了信号调理电路和信号反馈电路,通过实时对比反馈控制,解决了系统电路阻抗不匹配及干扰导致的激励信号相位不正交性和幅值不一致性的问题。实验结果表明：本文所设计的激励信号源输出信号幅值相对误差只有0.4%,正交性相对误差只有0.05%,并且采用该激励信号源,磁场式时栅传感器测角原始误差从±103.4"降低到了±20.3",有效抑制由于激励信号源幅值不一致和相位不正交带来的谐波误差。经修正后对极内角位移测量误差只有±1.3",整周角位移测量精度达到±2",满足高精度位移测量要求。

Measurement error analysis and system design for the excitation signals of high-precision magnetic-field time-grating sensors

To improve the measurement accuracy of magnetic-field time-grating sensors, the influences of harmonic error components on measurement accuracy which caused by inconsistent amplitude and nonorthogonal phase of the two channels of excitation signal sources are deduced theoretically. A design scheme of excitation signal sources for high-performance time-grating sensors is proposed based on DDS principles and closed loop feedback control. The FPGA chip is employed as the microprocessor, the frequency and phase of the output signal from the DDS are adjusted by configuring the frequency and phase control word based on subdividing the system clock by programming, and the accurate conversion form signal phase to signal amplitude is implemented using a gain controller and a phase accumulator. The signal conditioning circuit and the signal feedback circuit are proposed. After signal comparison, the feedback control is performed to solve the problems of the nonorthogonal phase and inconsistent amplitude caused by circuit impedance mismatch and interference signals. The experimental results show that the relative amplitude errors of the proposed excitation signal source is only within 0.4%, and the relative orthogonal errors are only within 0.05%. The original measurement errors of magnetic-field time-grating sensor using the proposed excitation signal source are reduced from 103.4" to ±20.3" which effectively suppresses harmonic errors caused by inconsistent amplitude and nonorthogonal phase of excitation signal sources. After error correction, the measurement accuracy of the sensor achieves ±2" in the angle range of 0°to 360°and ±1.2" within a polar, which meets the requirements of high-precision displacement measurement.