There are two rows of lights on one main interrogator, with each row of 8 lights as shown in figure 13. Therefore one main interrogator can connect with as many as 8 sub interrogators and 64 sensors accordingly. When the ICM system is in working condition, the main interrogator continually checks its sub interrogators one by one with each taking 2~3 seconds for checking its subordinating sensors. During the process, only one light in the first row is on at each turn, which indicates the state of the sub interrogator being checked. If the light is “green”, then the lights in the second row will be “green”, which indicates that all sensors subordinated to this sub interrogator are in good conditions. If the light is “red”, there must be one or more “red” lights in the second row, which indicates that the corresponding sensors are in bad conditions, suggesting that either cracks appear or sensors including wires are broken. Figure 13 The front view of main interrogator After installating ICM system, the aircraft returned to the service. In comparison with other same type aircrafts, the only additional thing for the mechanician of the aircraft is to check the lights on the main interrogators fixed in the landing gear cabin shown in Figure 12 before and after every flight. The mechanician can obtain the message immediately once he finds any “red” light based on the data analysis from the system. Besides the data recorded by the ICM system were collected and analyzed once per month. Up to now the aircraft with ICM system has been used more than 2 years, during this period, the working situations for both the aircraft and the ICM system run well as expected except some broken sensors transmit false signals. 4. Summaries It can prove by the present investigation that ICM system installed on the aircraft structure can monitor cracks which might occur at any specified location, and most sensors along with other hardware can operate normally and effectively under actual condition. Meanwhile, it is regrettable that some sensors located in the areas of high strain failed in short-time running, thus resulting in false signals. Therefore, more research is needed to design special sensors and corresponding splicing process for those high strain areas. Fortunately, a large progress has been made on this field which will be verified soon. In a word, ICM prototype installation is a significant first step in validating its effectiveness in operations and putting it into practical applications. Field data including false signals collected from operations provides useful results of the environmental effects on the ICM system and valuable information for ICM improvements. Acknowledgments This work was supported by the Chinese NSFC with grants of 51175404.
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