How to select sensor model and determine number of channels in acoustic emission detection?
Brief：The choice of sensor model mainly depends on the frequency of the measured acoustic emission signal
For general acoustic emission applications, the signal frequency band range is mostly 25kHz ~ 750khz, so the resonant sensor is more suitable. Metal materials and other applications often use the resonant narrow-band sensor with the general broadband frequency of 150kHz; for the corrosion, leakage and other acoustic emission signals, the resonant sensor with resonance frequency of 40KHz is often used; because the response sensitivity of broadband sensor is relatively gentle in a wide frequency band, the broadband sensor is selected for spectrum analysis.
The narrow-band resonant sensor has high sensitivity and high signal-to-noise ratio. It is cheap and has many specifications. For example, it is better to select the appropriate resonant sensor, such as sound source location, when knowing the basic characteristics of sound source propagation, and if you want to obtain the acoustic emission signal in a certain frequency band for processing or to improve the system sensitivity. It should be pointed out that the so-called resonant narrow-band sensor is not only sensitive to a certain frequency signal, but also sensitive to a certain frequency band, and the sensitivity of other frequency bands is relatively low. The user can select the appropriate sensor according to the use environment and the desired signal characteristics.
The sensor shell of QingCheng adopts high-quality stainless steel material with overall shielding design to effectively reduce interference; the contact surface is made of ceramic material to make the shell electromagnetically isolated from the measured object; each product has a unique serial number, which can track the production and test process; before leaving the factory, each sensor is tested for sensitivity according to <<GBT.19801-2005>>, and the products are attached with response curve.
The number of channels required for acoustic emission detection is mainly determined by the attenuation of acoustic signal in the material. Signal attenuation depends on the properties of the material and the frequency of the acoustic wave. Normally, the higher the density of the material, the less attenuation of the acoustic signal in the material. The lower the frequency of the acoustic wave, the less attenuation of the signal and the fewer channels required. However, the actual number of channels must be determined after attenuation test at the detection site.
According to previous AE detection experience, the AE frequency of metal crack signal is about 150kHz, leakage and wear signal is about 40kHz. Therefore, when detecting the crack signal of the metal, the acoustic emission sensor with a resonant frequency of 150kHz can be selected, and the spacing between the two sensors is not more than 7 meters. When detecting metal corrosion signals, acoustic emission sensors with resonant frequency of 40kHz can be selected, and the spacing between the two sensors is not more than 13 meters.
