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This paper designs a high-precision signal source based on DDS (Direct Digital Frequency Synthesis) technology for the needs of quartz wafer parametric testing system in π-network. Using Oven Controlled Crystal Oscillator (OCXO) as the time base, the signal source uses AD9959 integrated chipof the AD Company in American, and is controlled by ARM micro-controller.The signal source can generate four-channel...
IEC recommended π network zero phase method is the standard one for testing parameters of quartz crystal resonator. Main difficulty in realizing such method is the compensation for additional phase shift of π network. π network can be inspired by multiplexed output standard signal adjusted by phase difference. After testing the additional phase shift of π network, and then adjusting the phase difference...
Eddy current testing is an important and widely used method in non-destructive testing and evaluation. In this paper, an impedance analysis model of eddy current testing based on mutual inductance equivalent circuit is established using transmission line theory, and an analytical expression of impedance of the testing workpiece is obtained. Then the changes of impedance plane of ECT sensor affected...
In recent years, telecom operators have to bear increasingly intense competitive pressure, so how to provide customers with better service to enhance customer satisfaction and loyalty, which has become the first one of the issues that telecom operators face. This paper use factor analysis, model hypothesis testing and other means to study on Lishui Mobile Communication Company in Zhejiang province...
The temperature has violent influence on the test accuracy on the moisture content of crude oil by microwave. Establishing the affection of temperature, especially high temperature, plays an important role in improving the accuracy of detection. Indoor equipment of testing moisture content of oil-water mixture by microwave was built, which fulfill the test conditions with temperature 20°C-200°C and...
To investigate fire behavior in tunnel and improve fire protection in the ShiZiYang long-sized underwater railway tunnel, a series of fire testing were conducted. The scopes of the testing include temperature distribution and influential length of back-layering smoke flow in the tunnel under fire circumstance. The testing was conducted in a 1:9 scale model. The model tunnel had a circular cross-section...
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