Data acquisition system for fiber optic vibration monitoring
Distributed fiber optic vibration data acquisition system schematic
From the schematic diagram we can see that the distributed fiber optic vibration data monitoring system, using a balanced photodetector for coherent detection, and then need to IQ demodulation of the collected data, demodulation followed by phase unwinding to obtain the amplitude root phase data information.
IQ demodulation support
The amount of data before IQ demodulation and phase unwinding of the signal is very large and would consume a lot of computational resources if we were to perform this operation in our application software. Therefore, we implemented the IQ demodulation function with DAQ's FGPA hardware, which greatly reduces the amount of data computation. The DAQ hardware supports single-channel IQ demodulation, dual-channel IQ demodulation, and of course, raw data upload without IQ demodulation.
Built-in pulse output
The data acquisition method of distributed fiber optic vibration data acquisition system is to send out pulses first, and then perform data acquisition. In a traditional solution, we would use a separate waveform generator to trigger the waveform signal, which needs to be given to the AOM driver and the data acquisition card at the same time, and we need to ensure that the signal given to the AOM driver and the signal of the acquisition card should be clock synchronized, otherwise it will easily lead to jitter. In our PCIE-6920-DAQ acquisition card, we put the signal generator inside the acquisition card to support the signal trigger output to the AOM driver, and at the same time, we realize the clock synchronization inside the acquisition card. It effectively avoids jitter.
Interface
The data acquisition card with PCIe x8 interface, stable and reliable, stable driver can support windows and linux platform.
Sampling rate and supported fiber optic cable length
The data acquisition card can be configured for simultaneous upload rates of 250M, 125M, 83.33M, 62.5M, 50M;
When using the upload raw data, or single-channel demodulation function, the number of points per frame (the number of points collected by a single trigger pulse) can support a maximum of 131072 points, that is, the maximum length of a single fiber can reach 131072 * 0.4m = 52.4288 km at an upload rate of 250M (0.4 spatial resolution); if the upload rate is reduced, longer fiber lengths can be supported;
When using the dual-channel demodulation function, the number of points per frame (the number of points collected by a single trigger pulse) can support a maximum of 65536 points, i.e. a single fiber length at 250M (0.4m spatial resolution) upload rate can reach a maximum of 655536*0.4m=26.2144 km, with a total of 26.2144*2=52.4288 km for both channels of fiber; If the upload rate is reduced, longer fiber lengths can be supported.
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