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D/A and A/D Converters
Published in Jerry C. Whitaker, Microelectronics, 2018
A/D converters have a maximum sampling rate that limits the speed at which they can perform continuous conversions. The sampling rate is the number of times per second that the analog signal can be sampled and converted into a digital code. For proper A/D conversion, the minimum sampling rate must be at least two times the highest frequency of the analog signal being sampled to satisfy the Nyquist sampling criterion. The conversion speed and other timing factors must be taken into consideration to determine the maximum sampling rate of an A/D converter. Nyquist A/D converters use a sampling rate that is slightly more than twice the highest frequency in the analog signal. Oversampling A/D converters use sampling rates of N times rate, where N typically ranges from 2 to 64.
Apps for modal analysis to characterize the complex modulus of asphalt concrete
Published in Andreas Loizos, Imad L. Al-Qadi, A. (Tom) Scarpas, Bearing Capacity of Roads, Railways and Airfields, 2017
According to the Nyquist-Shannon sampling theorem the sampling rate should be at least twice of the highest measurement frequency (e.g. 20 to 30 kHz). However, due to the short duration time of the load pulse, the sampling rate was set to 500 kHz. This gives approximately 25 samples over the duration of the load pulse (~0.05 ms). The recording of the force and acceleration is triggered by the hammer impact. Note in Figure 2a and 3a that there is a pre-trigger time defined (0.1 ms) in order to capture the complete load pulse, which is important for accurate determination of FRFs. The record length is depending on the damping characteristics of the asphalt concrete, which changes with the temperature. Typical record lengths can vary between 2 (at ~ 40°C) to 30 (at ~ −20°C) milliseconds.
Background Material
Published in Wen-Qin Wang, Multi-Antenna Synthetic Aperture Radar, 2017
The term aliasing refers to the distortion that occurs when a continuous time signal has frequencies larger than half of the sampling rate. The process of aliasing describes the phenomenon in which components of the signal at high frequencies are mistaken for components at lower frequencies. If there are aliasing effects, the sampled apparent spectra fapparent will be [73] fapparent=fcontinuous−(round[fcontinuousfs])fs
Uniaxial tensile response of basalt fiber with different structures reinforced fine-grained concrete via acoustic emission monitoring
Published in The Journal of The Textile Institute, 2023
Minghao Jia, Kejing Yu, Kun Qian
The experimental setup was detailed in Figure 4. Tensile tests were conducted on Instron 3385H universal testing machine. Loading rate was 2mm/min. Steel clamping plates were used to apply the load, and the upper and lower clamping distance was 65mm. A pair of frequency resonant transducers were fixed on the specimens surface of by cloth tape to monitor the internal activities of the specimens. As detailed in Figure 4, the distance between the two transducers was 100mm for tensile tests. Acoustic coupling was improved by vaseline grease. The elastic waves were captured, transferred and stored in the form of electric signals (hits) using AEwin for Express-8 software. The sampling rate was defined as the number of samples extracted from a continuous signal in a unit time to form a discrete signal, which was expressed in Hertz (Hz). According to the Chinese specification GJB 6187-2008 (Commission of Science, Technology & Industry for National Defense, 2008), the sampling rate of the acoustic emission was 10 times that of the resonance frequency of the sensor. The sensor model used in this investigation was W500, and its resonance frequency was 500 KHz. As a result, AE hits (including waveforms) were recorded with a sampling rate of 5MHz (Soulioti et al., 2009; Dev et al., 2020). The amplitude threshold was set to 45dB to reduce the effect of environmental/electronic noise.
Deep reinforcement learning for continuous-time self-triggered control with experimental evaluation
Published in Advanced Robotics, 2023
By following the framework of the state-of-the-art RL algorithms mentioned in Section 1, the number of sampled data tuples is equal to the number of learning steps. However, an excessive sampling rate will significantly increase the number of learning steps, and the replay buffer will quickly fill up with the sampled data in just a few episodes, which is inefficient and can even reduce the effectiveness of the algorithm. The time spent interacting with the environment does not affect the data efficiency of the algorithm because it only depends on the complexity of the model (in model-based RL) or the properties of the real plant (in model-free RL), rather than the algorithm itself. Therefore, we consider that an algorithm following the mentioned framework requires fewer learning steps to succeed is more data efficient. In this context, reducing the sampling rate appropriately has the potential to utilize data more efficiently.
The development and tests of remote data acquisition and transmission system on civil engineering structural vibration
Published in Journal of Asian Architecture and Building Engineering, 2019
Ying-Qing Guo, Jie Zhang, Xing-Huai Huang
Data collection uses the DAQmx acquisition module of LabVIEW, its acquisition speed is fast and stable, and it is also compatible with most acquisition card. The data acquisition program is mainly composed of AI configuration, AI start acquisition, AI read data, and AI clear to complete the task. After completing the data acquisition, the acquisition tasks will be clear. The program should pay attention to several key parameters before operation: Selecting the correct acquisition channels and the measurement mode.According to Nyquist sampling theorem, sampling rate is more than twice the frequency of signal measurement. The practical measurements should be 5 ~ 10 times than the theoretical value.It should set the true number of DAQmx read function to read data from the cache, and set read number according to the current sampling rate.