Cost-Effective DAQ Boards For Distributed Acoustic Sensor DAS

The DAQ card has a 250MSps sampling rate suitable for DAS systems with 80M acousto-optic modulators (if your AOM is 200M, we recommend choosing our higher sampling rate version of the DAQ YB-DAS-1000-DAQ). The built-in IQ demodulation algorithm allows direct acquisition of amplitude data, which effectively reduces computational complexity.

This is a PCIe x8 Lane, dual channel, 14bits respectively rate high speed data acquisition card with 250MSps sampling rate. high performance FPGA chip on board with rich multiplier and RAM resources. The driver has good compatibility and supports multiple versions of WIN7, WIN8, WIN10 with 32/64bits, as well as CentOS and Ubuntu systems.

Description of built-in algorithms

YB-DAS-250-DAQ Built-in IQ demodulation function for balanced detector DAS system supports both single-channel and dual-channel IQ demodulation. Simultaneous upload rate can be configured as 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 captured by a single trigger pulse) can support a maximum of 131072 points, i.e., a single length of fiber at 250M (0.4m spatial resolution) upload rate, the  The maximum length of a single fiber can reach 131072*0.4m=52.4288km; if the upload rate is reduced, it can support longer fiber length;

When using the dual-channel demodulation function, the number of points per frame (the number of points captured by a single trigger pulse) can support a maximum of 65536 points, i.e., a single optical fiber length can reach a maximum of 65536*0.4m=26.2144 km at an upload rate of 250M (0.4m spatial resolution), and the total kilometers of two-channel optical fibers is 26.2144*2=52.4288 km; If the upload rate is reduced, longer fiber lengths can be supported.

Features

• 14bits dual-channel simultaneous real-time sampling
• 250MSps sampling rate
• DC coupling, 50Ω input impedance
• 2Vpp input voltage range
• 0-125MHz analog bandwidth (bandwidth can be customized)
• Up to 88dBc SFDR
• Trigger output pulse, 16-channel digital IO
• PCI Express x8 Lane high-speed transfer interface
• 2GB DDR3 cache

Specifications

API Interface Description

We provide the API in the form of a dynamic link library (.dll file) that you can call in your favorite programming language (e.g. python, C++, java or libview). Here is a description of the 2 more important functions.

int pcie6920_data_src_sel(unsigned int data_src_sel)

• Function description：
  

The digital down-conversion function has been done on the board to perform digital I/Q demodulation of the captured data. The data_src_sel parameter and the demodulation_ch_quantity are used together to select where in the demodulation algorithm the data should be read.

• Function parameter：

The data read by the pcie6920_read_data function should be parsed according to the following table：

ch0_data---ch1_data---I0---Q0---I1----Q1--- arctan(I0/Q0)--- arctan(I1/Q1)，These 8 types of data need to be parsed as 16-bit signed data (short)；√(I02+Q02)--- √(I12+Q12)，These two types of data need to be parsed as 16-bit unsigned short numbers.

The arctan phase value read up is a fixed point, and its correspondence with π is: 25733 - positive π, -25732 - negative π。The DAQ does not do phase unwinding internally and requires the user to do spatial and temporal unwinding in the application program, the unwinding method is shown in the following figure：

 int pcie6920_upload_rate_sel(unsigned int upload_rate_sel)

• Function description：

Setting the upload rate of IQ or phase/amplitude demodulated data reduces the amount of data uploaded for the same fiber length, but reduces the spatial resolution of individual samples.

• Function parameter：

upload_rate_sel：

1：Upload rate 250M, corresponding to a single-point spatial resolution of 0.4m；

2：Upload rate of 125M, corresponding to a single-point spatial resolution of 0.8m；

3：Upload rate 83.33M, corresponding to a single-point spatial resolution of 1.2m；

4：Upload rate 62.5M, corresponding to a single-point spatial resolution of 1.6m；

5：Upload rate of 50M, corresponding to a single point of spatial resolution of 2m；

Full interface documentation, please inquire.

Programming DEMO Example

# -*- coding: utf-8 -*-

from ctypes import *
import numpy as np
from time import sleep
import datetime

dll = cdll.LoadLibrary("./pcie6920_250m_64bits_api.dll")
samples = 1024 #Sampling Points
flag = True

def open_card():
    print('Open...')
    dll.pcie6920_open()   #open

def init_daq_card():
    print('Configure card...')
    dll.pcie6920_demodulation_ch_quantity_set(c_uint(1)) #Setting the number of channels requiring IQ demodulation
    dll.pcie6920_set_points_num_per_scan(c_double(1024)) #Set the number of points to be collected after each trigger pulse
    dll.pcie6920_set_scan_rate(c_double(20000))  #Setting the output frequency of the trigger pulse 20kHz
    dll.pcie6920_set_pusle_width(c_uint16(100)) #Setting the high level width of the trigger pulse, 100ns
    dll.pcie6920_set_center_freq(c_uint(80000000)) #Set the center frequency of the collected signal, if you only read the raw data you can not call the function
    dll.pcie6920_data_src_sel(c_uint(3)) #Setting the data source for reading
    dll.pcie6920_upload_rate_sel(c_uint(1)) #Set the rate at which data is uploaded
    print("Config end")


def start():
    flag = True
    print('Start...')
    dll.pcie6920_start()

def stop():
    flag = True
    print('Stop...')
    dll.pcie6920_stop()

def close():
    print('Close...')
    dll.pcie6920_close()  #先stop 再close

def read_data():
    n_frames = 200
    size = c_uint(0)
    buf = (c_int16*samples*n_frames)()
    flag = True
    i=0
    start_time = datetime.datetime.now()
    while flag:
        status_query = dll.pcie6920_point_num_per_ch_in_buf_query(byref(size))
        print(f"query.. {size.value}, {status_query=}")
        #print(size)

        if size.value >=samples*100:
            print('Read data...')
            status_read = dll.pcie6920_read_data(c_uint(samples*100), buf, byref(size))
            """ if size.value!=samples*100:
                continue """
            ndata = np.frombuffer(buf, dtype=np.int16)
            # print(f"Data size: {np.size(ndata)}")
            print(f"Start Time: {start_time}, Current Time: {datetime.datetime.now()} - Acquisition number {i}, {status_read=}")
            #unwrap code ....
            #flag = False
            i = i + 1
            if i >= 1000000:
                flag = False
            if status_read == -1:
                break
        else:
            sleep(0.1) #wait...


def run():
    open_card()
    init_daq_card()
    start()
    read_data()
    stop()
    close()


if __name__ == '__main__':
	run()

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