基于cRIO的瞬时转速测量方法研究

Research on Instantaneous Speed Measurement Methods Based on cRIO

为了实现利用增量式光电编码器对发动机曲轴瞬时转速的精确测量,提出了一种采用数字输入法测量瞬时转速。以cRIO板载的FPGA时钟作为时钟计数器,光电编码器脉冲作为触发计数器信号,实现光电编码器脉冲一个周期的计数,近而得到精确的瞬时转速。在1 000 r?min^(-1)转速下,随着采样频率增大,模拟输入法测量瞬时转速精度可以提高48%;模拟输入法测量该转速的误差达到1.772 r?min^(-1),而数字输入法误差为0.32 r?min^(-1)。在2 000 r?min^(-1)转速下,随着FPGA时钟频率的倍增,测量的转速越接近2 000 r?min^(-1)。由测量结果可以看出数字输入法和提高FPGA时钟频率对提高瞬时转速测量精度有重要意义。

A method of precise rotary speed measurement with digital input method was proposed to improve the measurement accuracy of rotary speed of engine crankshaft measured with incremental photoelectric encoder.To get accurate instantaneous speed,it is necessary to achieve a periodical count about photoelectric encoder pulse,considering cRIO onboard FPGA clock as a clock counter and photoelectric encoder pulse as a trigger counter signal.At 1 000 r?min^(-1) speed,with sampling frequency increasing,the instantaneous speed accuracy measured by analog input method can be improved by 48%;the error was 1.772 r?min^(-1) which analog input method measures speed,however,the error about digital input was 0.32 r?min^(-1).At 2000 r?min^(-1) speed,the measured speed was closer to 2000 r?min^(-1) with the FPGA clock frequency multiplier.The results show that digital measurement and increasing FPGA clock frequency are important to improve the measurement accuracy of instantaneous speed.