Volumen 22 (2022): Heft 5 (October 2022)

A stable and reliable time keeping system depends on the integrity monitoring of the atomic frequency standard. This paper reports a scheme for autonomous integrity monitoring of multiple atomic clocks, which combines the frequency standard comparison method and the frequency jump detection method. The frequency standard comparison method uses multi-channel synchronous acquisition technology and digital frequency measurement technology to realize the precise measurement of multiple atomic frequency standards. The frequency jump detection method uses adaptive filtering to predict the relative frequency difference and give an accurate and timely alarm for the abnormal of frequency jump. The results show that the noise floor frequency standard comparator is better than 6.5×10⁻¹⁵ s. For a relative frequency deviation of 2.0×10⁻⁶ Hz, the probability of anomaly detection is almost 100 %. The system has high frequency measurement resolution and fast alarm of frequency jump, which can meet the real-time requirements of a time keeping system for the integrity monitoring of multiple atomic clocks.

In aircraft construction, when creating samples of new equipment, shock tests are often performed, both on individual components and the entire product. It requires introducing non-destructive testing devices into production, it is one of the most important factors in accelerating scientific and technological progress, raising the quality and competitiveness of manufactured products. Applying modern means of non-destructive testing, there is the problem of their protection from external vibrations, which affect the sensitivity, accuracy and reliability of high-precision measurements. In such cases, the conversion of measuring information during powerful vibration and shock tests, as a rule, is carried out by piezoelectric acceleration sensors. Although to provide impact testing, there is a need to develop and use stand-alone recorders. The main requirements for these recorders are to ensure the autonomy and operability of the recorder onboard the test product and to ensure the synchronization of the registration of the shock load.

The existence of related faults between components brings great difficulties to the analysis of the importance of system components. How to quantify the influence of related faults and evaluate the importance of components is one of the hot issues in current research. In this paper, under the assumption that the fault propagation obeys the Markov process, the PageRank algorithm is integrated into the decision-making trial and evaluation laboratory (DEMATEL). On the basis, the calculation of influencing degree and influenced degree between components is studied to quantify the influence of related faults, and the problem of subjective evaluation of weight coefficient in traditional DEMATEL is solved. The rationality is verified through the method of combining the Interpretative Structural Modeling Method (ISM) and direct relation matrix. The importance of system related faults is identified accurately based on the calculation of center degree and cause degree, and the central-related faults of CNC machine tools are analyzed as an example to verify the effectiveness of the proposed method.

The maximum electromagnetic field formed in the electrically large enclosures for a given input power has always been the focus of electromagnetic compatibility issues such as radiation sensitivity and shielding effectiveness. To model the maximums in a simple manner, the electrically large enclosure can be regarded as a reverberation chamber (RC), thus the generalized extreme value (GEV) theory based framework is used for both undermoded and overmoded frequencies. Since the mechanical stirrer is not easy to be installed like that for RC, frequency stirring and mechanical stirring related configurations are discussed, and the corresponding results have confirmed the validity of frequency stirring with the estimate of the parameters in GEV distribution. As for the maximum field, a comparison has been made between GEV distribution and IEC 61000-4-21, and the corresponding results have also highlighted that the maximum field can be assessed by frequency stirring configuration, and by GEV distribution with a desired confidence.

With the development of semiconductor assembly technology, the continuous requirement for the improvement of chip quality caused an increasing pressure on the assembly manufacturing process. The defects of chip pin had been mostly verified by manual inspection, which has low efficiency, high cost, and low reliability. In this paper, we propose a vision measurement method to detect the chip pin defects, such as the pin warping and collapse that heavily influence the quality of chip assembly. This task is performed by extracting the corner feature of the chip pins, computing the corresponding point pairs in the binocular sequence images, and reconstructing the target features of the chip. In the corner feature step, the corner detection of the pins using the gradient correlation matrices (GCM), and the feature point extraction of the chip package body surface using the crossing points of the fitting lines are introduced, respectively. After obtaining the corresponding point pairs, the feature points are utilized to reconstruct the three dimensional (3D) coordinate information in the binocular vision measurement system, and the key geometry dimension of the pins is computed, which reflects whether the quality of the chip pins is up to the standard. The proposed method is evaluated on the chip data, and the effectiveness is also verified by the comparison experiments.

The electron collection efficiency (CE) of the photomultiplier tube based on microchannel plates (MCP-PMT) is limited by the MCP open area fraction. Coating MCP with a high secondary yield material is supposed to be an effective approach to improve CE. Both typical and coated MCP-PMTs are developed. A relative measurement method is proposed to characterize the collection efficiency performance. Results show that the PMT based on the coated MCPs has a significant improvement on CE, a good gain uniformity and a high precise energy resolution.