Operating principle: Sensors with integrated acoustic emission systems have been developing by KERT for three years. Now the second generation of these sensors is presented. The sensor housing contains an analog section, a digital signal processing unit and a web server. The analogue part amplifies the sensor signal and forms the logarithmic envelop for data reduction. AE parameters such as arrival time, rise time, duration, peak amplitude and energy are extracted from the envelope by the digital signal processing unit. In parallel to the parameter extraction, the waveform of the envelope can be recorded. The web server generates dynamic web pages to control the sensor and to display the measurement results. The sensor is either wireless (type WiFi) or via Ethernet cable (type PoE) connected to a data network.
Type WiFi: The data transmission takes place in the 2.4 MHz band. A lithium accumulator of standard size 25500 takes over the power supply. An obvious advantage is that no cable is necessary. The maximum hit rate over all channels is between 1.5 and 20 kHits/s, depending on other traffic in the 2.4 MHz band. The lithium battery allows operating times of at least 8 hours. 24 hours are achieved at low hit rates. The power consumption of one sensor is less than 1.64 W.
Type PoE: An Ethernet cable is used for both power supply and data transmission (Power over Ethernet). The maximum hit rate over all channels amount to 300 kHits/s. The power consumption of one sensor is less than 0.88 W.
Types WiFi.L and PoE.L: Sensors with the type designation L at the end have a submicrosecond precise time synchronization. Together with a so-called Mid Device, it is possible to set up sensor networks that allow location of the AE sources. Here the Mid Device creates the dynamic web pages. For the PoE variant, only cable lengths are required that correspond to the sensor distances. This is a significant advance over locating systems with pure centralized signal processing.
Improvements over the 1st generation:
The piezoelectric element and the analog part are matched to each other to achieve optimum sensitivity of the sensors. The adjacent figure shows a typical frequency behavior.