In dynamic vibration monitoring, how is the balance achieved between the demodulator's sampling frequency and phase noise? What is the minimum detectable strain resolution (nε/√Hz)?

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In dynamic vibration monitoring, how is the balance achieved between the demodulator’s sampling frequency and phase noise? What is the minimum detectable strain resolution (nε/√Hz)?

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For dynamic vibration monitoring with Fiber Bragg Grating (FBG) demodulators, achieving a balance between sampling frequency and phase noise is crucial for accurate data acquisition.

  1. Sampling Frequency vs. Phase Noise:

    • Sampling Frequency: A higher sampling frequency allows for the capture of faster dynamic events and provides a more detailed representation of the vibration waveform. However, increasing the sampling frequency often means a broader measurement bandwidth, which can potentially introduce more noise into the system if not adequately managed.
    • Phase Noise: Phase noise in an FBG demodulator primarily affects the stability and precision of the wavelength measurement. High phase noise can mask small wavelength shifts caused by dynamic strain, particularly at higher frequencies.
    • Balance: The balance is typically achieved through careful design of the demodulator’s optical and electronic components. Advanced signal processing techniques, such as filtering and averaging, are employed to suppress phase noise while maintaining a high effective sampling rate for dynamic events. The choice of sampling frequency should be at least twice the highest frequency component of interest in the vibration (Nyquist theorem), but going significantly higher without proper noise mitigation can degrade signal-to-noise ratio.

  2. Minimum Detectable Strain Resolution (nε/√Hz):

    • The minimum detectable strain resolution (often expressed in nε/√Hz) is a fundamental specification that indicates the demodulator’s ability to resolve very small strain changes in a given measurement bandwidth. A lower value signifies a more sensitive and precise system.
    • This parameter is influenced by several factors, including the demodulator’s internal noise floor, the stability of its light source, the performance of its detection electronics, and the quality of the FBG sensor itself.
    • OFSCN® Fiber Bragg Grating Interrogators are designed to offer excellent strain resolution, enabling precise dynamic measurements. The typical strain resolution for high-performance FBG interrogators can range from sub-pico-strain to a few nano-strain per square root Hertz, depending on the specific model and its operating parameters.

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OFSCN® Fiber Bragg Grating Interrogator