Eight-channel signal synchronous acquisition system based on PCI and LabVIEW

In response to the multi-channel acquisition of the power grid simulator data collection system, this article builds a 8-channel signal synchronization acquisition system based on PCI-1706U and LabView, which introduces the characteristics of PCI-1706U hardware and LabView software DAQ system. A LabView DAQ program that uses the PCI-1706U to collect 8-way signal from the signal generator, complete the experiments of multi-channel synchronous acquisition and delayed start to collection, verify the feasibility and stability of the system, and analyzed the collected signals. Finally, the main work and innovation points of the thesis are summarized, and suggestions and outlook for future improvement are given. This study provides an effective implementation method based on PCI-1706U and LabView multi-channel signal synchronous acquisition system and delay acquisition function, with certain application value and promotion space.


Introduction
Modern industry is developing rapidly.An important requirement in computer technology is to collect production data in the process of industrial production [1] .DAQ refers to the process of measured electrons and physical phenomena such as computers and peripheral I/O devices to measure voltage, current, temperature, or pressure.The traditional data collection system mostly uses DSP as the core chip, but the DSP chip consumes great power and is difficult to control the peripheral circuit [2] .Compared to using technologies such as DSP or FPGA to build a data acquisition system, the use of PCI data collection cards does not require additional hardware design and programming.PCI bus, as a advanced high -performance 32/64 local bus, has higher bandwidth, which is very suitable for computer and peripheral equipment for high -speed data exchange.It has replaced the original IS bus the mainstream bus of the system [3] .In the LabView2020 programming software environment, this article uses the PCI-1706U produced by Advantech to simultaneously collect the 8-way signal issued by the signal generator and can achieve any time delay.

Hardware selection
The hardware section of the collection system includes two signal generators, Advantech PCI-1706U data collection cards, and industrial control machines.The models of the signal generator are DG1022U and DG1032Z produced by Rigol, with two and three ouput channels respectively.PCI1706 has 16 single-end or 8 differential analog input channels.The maximum sampling rate of the collection card can reach 250k s/s per channel, so that it can capture high-frequency signals and provide accurate sampling results.the card has flexible triggering and synchronous functions, supporting multi-card synchronization to achieve multiple devices for more complex data collection and control tasks [4] .

System design
During data transmission, use the PCI bus into high -speed data exchange [5] .The DAQ device is an interface between the computer and the external signal.It has the ability to receive and output electrical signals.It can make the input analog signal digitization [6] .This article enters the 8 -way differential simulation signal, which eliminates the impact of environmental interference through differential input [7] .Figure 1 sets the sinusoidal signal with two frequencies from the bidirectional outputs of the two signal generators with an amplitude of ±5V:

Collection system software platform composition
The software part of the acquisition system is mainly LabView developed by NI.LabView language is a graphical programming language.The program design is relatively simple, which is convenient for users to design the design of the upper machine human aircraft interface [8] .LabView provides rich built -in functions and tool packages, which can simulate and control various actual instruments.In addition, it has powerful data processing and analysis functions, supports extensive hardware, and seamlessly integrates with other equipment and systems [9] .This article mainly uses the DAQmx driver in LabView to achieve communication with the data acquisition card.This program provides a set of API interfaces to enable LABVIEW to control and read the input and output of the data collection card.

DAQNavi Create Channle module
Create an analog input or output channel in the LabView environment.The channel object will be associated with a specific device and channel, and the parameters of the channel will be determined, such as physical channels, signal types, input or output range, sampling rate, gain, etc.This article sets the AI0-7 analog input port with the physical channel of PCI-1706U.After querying the pin according to the panel card use manual, the signal generator and the data collection card are connected by a differential method.Set the input range to ± 5V.

DAQNavi Timing module
Timing is a time-based trigger mode in data acquisition, which is used to control data acquisition equipment to sample or realize timing function within a specific time interval.In this article, the modulus conversion rate is 1000Hz.According to the Narquist sampling theorem, in order to accurately restore the signal, the sampling rate should be at least twice the frequency of the original signal.In order to reduce the incidence of distortion or confusion when the restore signal occurs, consider setting the sampling rate per channel to 100kHz.Ten times the signal frequency [6] .

DAQNavi Trigger module
Trigger is a trigger signal used in data collection to control sampling.When specific conditions are met, the trigger signal trigger data acquisition device begins to collect data.When the input signal meets the preset conditions, the trigger module sends a trigger signal to the data acquisition system to trigger the data collection start to sample.Through the trigger function, multi -channel and multi -device are synchronized.After selecting the device, the trigger source is set to AI0.

DAQ Read module
The read module shown in Figure 3 below is used to configure and perform data read operations.In this article, the signal reading type is set to a waveform type with multiple channels, and you can also configure the read accuracy, read duration, and so on.Set the read rate of 100,000 samples per channel to match the number of sample.It should be noted that the matching of the collection speed and reading speed.According to the principle of data collection, the external data is stored in the FIFO of the data collection card after certain processing.When the FIFO capacity reaches a certain amount, it will be uploaded to a computer buffer, and then reads data in the buffer through DAQNavi [10] .If the reading speed is too small compared to the collection speed, it cannot be read enough from FIFO to the collected data, which may cause data in FIFO to be covered and cause data overflow loss.

While circulation structure
In the DAQ module of LabVIEW, the while loop structure can be used to realize the real-time loop execution of data acquisition and control tasks.By calling the daqmx function, configure the loop conditions and the code block in the loop body, read the data in the cache of the data acquisition card for subsequent processing.So this experiment uses while loop to realize continuous data collection.

Signal collection results
The overall device diagram of the experiment is shown in Figure 4. Before the specific experiment, the is used to test the signal to ensure that the signal generator accurately sends out 8 sinusoidal signals.The LabVIEW program includes a program block diagram and a front panel.The front panel is used to set user input and display program output to simulate the front panel of a real instrument, as shown in Figure 5.The program block diagram is to control the indication quantity on the front panel by using the graphic language [11] , as shown in Figure 6.

5.Conclusion
In this article, the data collection system with PCI-1706 and industrial control machines is the main hardware platform.Using Advantech's DAQ control to collect the 8-way split signal issued by the two signal generators for efficient and accurate collection and achieve delayed collection of any data delayed collection.In addition, it is designed on the LabView front panel to achieve good human -computer interaction and display the collected signals in real time.It can be widely used in a variety of high -speed data acquisition fields, with versatility and expansion.In the future, it can gradually be realized in more accuracy of more channels.

Figure 1 .
Figure 1.Signal generator.Insert the PCI1706 data collection card into the industrial control machine card slot, lead the analog input source from the signal generator, and input the distribution of pins in the simulation quantity input pins of the PCI1706, and connect the 8 -way signal separately.Use a differential form to connect the signal generator to the data collection card.This is shown in Figure2below.

Figure 2 .
Figure 2. connection between signal generator and data collection card.

Figure 6 .
Figure 6.Labview program diagram.The left side of the front panel displays the parameters that can be changed instantly.The right side reads the 8-channel real-time signals.It can be seen that due to the different types of signal generators, the accuracy and stability are slightly different, and the signals collected by different generators are slightly different, but the sine wave signals collected in each four channels are accurate and consistent.