Design of multi-channel data acquisition system based on LabVIEW and NI PXI-5105

XIE Ya-ni, ZHANG Zhi-jie

(Key Laboratory of Instrumentation Science & Dynamic Measurement (North University of China),Ministry of Education, Taiyuan 030051, China)

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Design of multi-channel data acquisition system based on LabVIEW and NI PXI-5105

XIE Ya-ni, ZHANG Zhi-jie

(KeyLaboratoryofInstrumentationScience&DynamicMeasurement(NorthUniversityofChina),MinistryofEducation,Taiyuan030051,China)

A data acquisition system based on LabVIEW and NI PXI-5105 is presented for multi-channel data acquisition. It can realize the functions of parameter setting, data acquisition and storage, waveform display and data analysis using LabVIEW and NI-SCOPE device driver. The advantages of the system are that the setting is convenient, the operation is easy, the interface is friendly and the functions are practical. The experiment results show that the system has good stability and high reliability and is a powerful tool for multi-channel data acquisition.

LabVIEW; multi-channel data acquisition; PXI-5105

0 Introduction

The traditional data acquisition system generally consists of hardware acquisition circuits and single chip microcomputer. But there are some deficiencies in the data acquisition system based on single chip microcomputer, such as small storage capacity, slow operation, long development cycle and poor extensibility. Therefore, it is very difficult to meet the requirements of modern engineering applications in high-speed, mass-storage and multi-channel acquisition. With the rapid development of computer, acquisition circuits and network technologies, virtual instrument technology is widely used in the fields of measurement, data acquisition, etc[1]. In this paper, a multi-channel data acquisition system based on NI PXI-5105 data acquisition card and LabVIEW soft platform is presented. This system includes upper computer ( PC and the software ) and lower computer ( acquisition circuits ), the upper computer controlling the lower computer[2]. LabVIEW graphical programming language has strong ability of external programming interfaces including dynamic link library (DLL), code interface node (CIN), ActiveX, Matlab, etc., which contributes to easy hybrid programming with other high-level languages[3-4]. Besides, it also provides a lot of special tools and drivers, such as NI-SCOPE, by means of which, almost any hardware interface can be connected with LabVIEW. Especially, it is suitable for high-speed, mass-storage and multi-channel data acquisition.

1 System design idea

The designed multi-channel data acquisition system consists of sensors, signal conditioning device and NI data acquisition device, as shown in Fig.1. The data acquisition device is composed of six parts: chassis, monitor, keyboard, controller, NI PXI-5105 data acquisition card and software.

Compared with the traditional piezoelectric sensor, integrated circuits piezoelectric (ICP) sensor has high accuracy and reliability, which makes it suitable for use in field tests and on-line monitoring. Therefore, ICP sensor is chosen in this design. Fig.2 shows the components of basic ICP sensor. Piezoelectric element and ICP source follower amplifier are joined together as an inseparable sealed assembly when manufacturing.

Fig.1 System block diagram

Fig.2 Components of basic ICP sensor

The main task of hardware system is to acquire analog signals output by ICP sensors and then convert them into the digital signals which are transmitted to the computer finally. The software system consists of computer system software and multi-channel data acquisition system software which are programmed by LabVIEW language for data acquisition, display and processing in order to monitor physical quantities[5]. After connecting the hardware devices and setting PXI-5105 parameters, the acquired data is stored in the format of technical data management streaming (TDMS) file to the specified file path. And then the stored data file is read and processed. Finally, data display, calibration, filtering, report generation, etc. are realized and multi-channel data acquisition is completed[6].

2 System design

2.1 Hardware design

Because general signal conditioning circuit is limited to the number of channels, it cannot meet the requirements of the system design. Considering that YE3826A constant current regulator can provide power supply for 12 ICP sensors at the same time and the output signals of the ICP sensors after amplification, filtering and other needed processing can be used for further display, collection and analysis, therefore, YE3826A is selected for signal conditioning circuit. In addition, YE3826A has the advantages of high precision, low noise, adjustable constant current source, adjustable gain and multi-channel structure.

Generally speaking, the data acquisition device is affected by sampling rate and transmission rate. To solve this problem, a high-resolution, NI PXI-5105, is adopted. It has eight simultaneous input channels with the sampling rate of 60 MS/s, the resolution of 12 bits, the bandwidth of 60 MHz, the memory in a compact to 512 MB and independent channel-selectable input impedance of 50 Ω or 1 MΩ[7]. NI PXI-5105 is ideal for wide range applications in ultrasonic nondestructive test and military.

This paper uses PXI bus technology, PXI means PCI eXtensions for Instrumentation and PCI means peripheral component interconnection. PXI bus combines the electrical bus characteristics of PCI, the sturdiness of compact PCI and the mechanical packaging characteristics of Eurocard[8-9], therefore, it has high data transmission speed, strong package and high-performance international electrotechnical commission (IEC) connector. In addition, it has star trigger bus for precise timing, local bus for high-speed communication and reference clock for multi-board synchronization[10]. In this way, PXI bus is very suitable for measurement and data acquisition due to high data transmission rate, easy integration, small size, high reliability and high cost performance ratio.

2.2 Software design

The software system of the multi-channel data acquisition system is mainly to achieve the following functions: ① parameter setting, including data length, sampling frequency, amplitude, channel selection, trigger type, trigger source, etc.； ② reading data, waveform display and saving required data；③ reading the stored data file； ④ converting voltage value (V) to pressure value (kPa) according to the sensor sensitivity of the corresponding channel； ⑤ selecting a certain part of the waveform, saving and analyzing; ⑥ data filtering; ⑦ generating report[11].

The software modular diagram is shown in Fig.3.

Fig.3 Software modular diagram

3 System implementation

NI-SCOPE is the driver for NI PXI-5105. It can seamlessly integrate all hardware functions of NI PXI-5105 into LabVIEW. By calling the related functions of NI-SCOPE, the system functions of initialization, parameter setting, start data acquisition and stop data acquisition are implemented.

3.1 Parameter setting

The function of parameter setting is accomplished by calling NI-SCOPE subVI, such as niScope Initialize.vi, niScope configure chan characteristics.vi and niScope Configure Trigger Immediate.vi. In this way, the needed parameters are set, including data length, sampling frequency, amplitude, channel, trigger type, trigger source and so on.

Each parameter has a default value, by receiving the parameter control command to get the set value as needed.

3.2 Reading data

The block diagram of reading data module is shown in Fig.4. After setting parameters, starting acquisition command is sent to lower computer by niScope Initiate Acquisition.vi, then data acquisition card keeps an idle state, waiting for trigger； after being triggered, the multi-channel data and the waveform information (actual sampling rate, offset, gain, etc.) are read back by niScope Fetch.vi and displayed on waveform graph. Thus, the data acquisition stops by niScope Abort.vi.

Fig.4 Block diagram of reading data module

3.3 Data extraction

Generally, the valid data is only part of the acquired data, therefore, the data must be extracted as needed. Fig.5 shows the cursor first, and according to two positions of X cursor, the range of the interested data can be determined. And then the valid data can be extracted by split array function[12]. In this way, the waveform analysis of valid data becomes simple and memory resources are saved.

Fig.5 Block diagram of data extraction

3.4 Filter analysis

Filter is used to filter the specific frequency for shielding unwanted signal. Because the data are from different channels, in filter analysis module, the data is chosen first and then one filter is selected from the following filters：buterworth filter, elliptic filter, FIR filter, etc. One filtering method is chosen from the following methods: low-pass, high-pass, bandpass and band-stop filters. The parameters of cut-off frequency and order are set. Finally, the function of filter analysis is completed by calling IIR Cascade Filter.vi.

3.5 Data storage

TDMS file format is adopted as a result of the deficiencies of other data storage options commonly used in test and measurement fields. The binary TDMS file format is an easily exchangeable, inherently structured, high-speed-streaming-capable file format. This file format is structured using three levels of hierarchy: file, group and channel. In addition, the file level can contain an unlimited number of groups and each group can contain an unlimited number of channels, which makes the data organization easy to be understood.

Block diagram of data storage is shown in Fig.6. Choose the storage path and file name are chosen firstly by file dialog, then use function “TDMS Open” is used to open the file and write the data to TDMS file by function “TDMS Write” . If data storage is completed, the file is closed. At the same time, a dialog of “success” occurs and indicates that the data storage is successful.

Fig.6 Block diagram of data storage

4 Results and conclusion

Using graphical programming software LabVIEW and powerful driver NI-SCOPE, combined with advanced PXI hardware platform and data acquisition device, a multi-channel data acquisition system based on PXI-5105 is constructed rapidly. This system realizes the functions of simultaneous acquisition of multi-channel signal, waveform display, data analysis and storage. The system human-machine interface is shown in Fig.7.

Fig.7 System human-machine interface

The experiment results of multi-channel data acquisition is shown in Fig.8.

Fig.8 Experiement results of multi-channel data acquisition

After experiment verification, multi-channel data dcan be acquired at the same time in this system,the users can display and analyze the data through the upper computer conveniently and quickly, and the designed multi-channel data acquisition system is stable, accurate and reliable. Compared with traditional ata acquisition system, this system possesses the following features: short development cycle, strong extensibility, stable performance, strong versatility, high cost performance, easy operation, etc. LabVIEW simplifies the programming process, especially the use of the SCOPE driver greatly simplifies programming. Users only need to modify the code according to the actual functional requirements and can easily complete system extension. Therefore, the system has good adaptability, flexibility and practical value.

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基于NI PXI-5105的多通道數(shù)據(jù)采集系統(tǒng)的設計

解亞妮， 張志杰

(中北大學 儀器科學與動態(tài)測試教育部重點實驗室， 山西 太原 030051)

描述了基于LabVIEW軟件和NI PXI-5105的多通道數(shù)據(jù)采集系統(tǒng)。 利用LabVIEW和NI-SCOPE， 實現(xiàn)了系統(tǒng)的參數(shù)設置、 數(shù)據(jù)采集和存儲、 波形顯示以及數(shù)據(jù)分析等功能。 該系統(tǒng)設置簡便， 操作簡單， 界面友好， 功能實用。 實驗結果表明， 系統(tǒng)具有良好的可靠性和穩(wěn)定性， 是進行多通道數(shù)據(jù)采集的有力工具。

LabVIEW； 多通道數(shù)據(jù)采集； PXI-5105

XIE Ya-ni, ZHANG Zhi-jie. Design of multi-channel data acquisition system based on LabVIEW and NI PXI-5105. Journal of Measurement Science and Instrumentation, 2015, 6(1): 7-12.

10.3969/j.issn.1674-8042.2015.01.002

XIE Ya-ni (xieyani163@163.com)

1674-8042(2015)01-0007-06 doi： 10.3969/j.issn.1674-8042.2015.01.002

Received date： 2014-10-29

CLD number： TP274 Document code： A