电站锅炉声学测温中的声源选择及其声信号互相关特性分析

Selection of Sound Sources and Cross-correlation Characteristic Analysis of Acoustic Signals in Acoustic Pyrometry in Boilers

以选择声学测温中的声源和声信号为目的,针对电站锅炉的声学特性,分析了声学测温中的声信号的频率范围、声压级要求。比较了火花放电声源、电动声源和气动声源的优缺点,建议采用频率在1.5～10kHz,声压级大于120dB(0dB=20μPa)的气动声源。用Matlab编写程序并驱动扬声器发声,基于MKⅡ多通道声学测试分析系统,对几种典型声信号进行了常温下的互相关特性分析实验研究,指出了正弦信号不适合作为声学测温的声信号:扫频信号则要尽量减小扫频周期。提出了一种新的信号,伪随机二进制序列,在常温下的实验结果和理论上尖锐的互相关特性分析一致。利用压缩空气机作为气动声源,由频谱分析可知其具有类似白噪声的频率特性,互相关特性分析实验结果很好,进一步证明了气动声源的喷射声信号在测量精度上的优势。不仅为声学测温中的声源选择提供了指导,而且互相关特性分析对锅炉四管泄漏声源定位中的延时测量有一定的参考价值。

In purpose of selecting of sound source and signal in acoustic pyrometry, according to the acoustic characteristic of boiler in power plant, the requirement of frequency range and sound pressure level in acoustic pyrometry is analyzed. The characteristic of spark gaps, electric and pneumatic sound sources are compared. The pneumatic signal with frequency range of 1.5-10kHz and SPL of 120 dB is recommended. Based on MKⅡ multiple channels acoustic measurement system and speakers driven by Matlab procedures, the cross-correlation characteristic of several typical acoustic signals are experimented. The results show that the sine signal is not adaptive to be used and the chirp signal can be used with short chirp period. The experiment result of a new signal, pseudo-random binary sequence （PRBS） with acute cross-correlation characteristic, is accordant with the theory analysis. The high pressure air machine is used and the experiment result is well. The frequency characteristic of pneumatic sound signal is similar to the white noise. Not only the sound source selection is offered in acoustic pyrometry, but also some reference value is shown to time delay measurement in sound source location of tube leakage in boiler.