Students Learn Data Acquisition and Analysis Using LabVIEW

Author(s):
Alex See, PhD - Monash University Malaysia School of Engineering and Science

Industry:
University/Education

Products:
PXI/CompactPCI, LabVIEW

The Challenge:
Teaching mechatronics students data acquisition and signal processing fundamentals.

The Solution:
Having students design, develop, and test a LabVIEW-coded software program for data acquisition, signal measurements, and fundamental digital signal processing (DSP) using the FFT (Fast Fourier Transform).

Introducing Students to Digital Signal Processing
Monash University Malaysia believes that mechatronics students should have some insight into the fundamentals of DSP and data acquisition in this advanced computer era. Second-year mechatronics students at Monash University Malaysia are required to enroll in a course module known as Project and Practice, which develops and constructs student ”soft” and ”hard” skills, including analog-to-digital conversion, sampling, and signal processing implementation, through a hands-on approach. This module, which comprises a one-hour lecture and three hours of laboratory work per week, lasts for 13 weeks in the second semester of each year.

Last year, 12 students enrolled in the Project and Practice Module. They divided into four groups, and each group worked to solve a different project challenge. The projects involved using the FFT to develop a real-time data acquisition system with signal processing capability. The students code-named their project “LAVINST.”

The LAVINST Project: A Course Centered on LabVIEW
LAVINST encompasses complete virtual instrumentation by using an industry-standard computer or workstation equipped with powerful application software, cost-effective hardware such as plug-in boards, and driver software. Students developed and customized a virtual instrument to perform data acquisition, measurements, and fundamental signal processing by using a National Instruments PCI-6036E series plug-in board and NI LabVIEW, which we chose due to its recognition as a very powerful tool for data acquisition in a test and measurement environment.

This student project required software supporting:
· Real-time data acquisition
· Signal analysis
· Data visualization and presentation

One criterion in choosing the course software was its ease of interfacing and communicating with data acquisition hardware. LabVIEW-based applications have shown very promising results, as LabVIEW instantaneously transforms the PC into a virtual instrument, providing an easy-to-use, application-development environment designed specifically to meet engineer and scientist needs. LabVIEW ease of use and rapid prototyping quickly helped students learn and implement fundamental signal processing, especially if the student has a background in computer programming.

Additionally, because National Instruments offers a wide variety of hardware to complement NI software, we chose to use National Instruments Measurement & Automation Explorer (MAX).

These students had no prior LabVIEW knowledge or experience, so the course offered them a chance to understand the nature of LabVIEW programming through a four-hour intensive lecture. During the lecture, instructors explained the LabVIEW environment, including windows, menus, tools, front panels, block diagrams, dataflow programming, and tool palettes.

The lecture also taught students about the commonly used structures in programming, including the “while,” “for,” and “case” structures, as well as the “sequence” feature available in the function palette at the block diagram level.

The Single-Sided Fast Fourier Transform Approach
To develop fundamental knowledge, students first investigated the single-sided FFT by using LabVIEW without the data acquisition board. Once the students understood the fundamentals of FFT, they proceeded with data acquisition and measurement. Students used the VI for continuous data acquisition with FFT and added power spectrum integration into their block diagram. They used local and global variables to eliminate very messy diagram wiring.

Student LabVIEW block diagrams generated three different types of signals – a DC offset and two user-defined sine wave signals. The three signal profiles are shown as a combined sine waveform, and the single-sided FFT profile is shown at the end as an FFT spectrum.

The students designed their VI so they could vary three different signals via the control and summarize and display the results.

For this project, students started the data acquisition by configuring the device number, channels, and buffer size with the AI Config VI. The AI Start VI sets the sampling frequency and starts the acquisition, assigning a constant zero to signal the AI Start VI to start a continuous buffered acquisition. The AI Read VI located inside the while loop reads the data from the buffer with the specified number of samples. The acquired data plots on the waveform graph.

To prevent buffer overflow, the number of samples cannot be set equal to the buffer size. If the scan backlog increases steadily, the buffer might overflow and generate an error. Normally, the number of samples is set to one-fourth or one-half the buffer size for a continuous acquisition.

Students used NI MAX for configuration and testing, verifying that the data acquisition board worked properly. NI MAX includes a way to self-test device resources (such as analog, counter, and digital input and output) by clicking on the test panel menu.

An additional LAVINST project front panel contains various slider switch controls. When the program was running, students clicked the desired slider switch control to launch a pop-up window for the specified function (real time, spectral analysis, and power spectrum). The student-coded program provided various measurements after input analog signal real-time data acquisition, including:
· DC value
· Decibel
· Peak-to-peak
· Fundamental frequency
· Percent total harmonic distortion
· Root-mean-square

Hands-On, Practical Programming Experience
With the LAVINST program, students performed real-time data acquisition, measurement, and fundamental signal processing using LabVIEW. Students acquired a better understanding of the signal processing and data acquisition fundamentals. LabVIEW ease of use, coupled with its power and flexibility, are noteworthy advantages in developing hands-on student learning experiences. While students with basic programming language knowledge and experience are at an advantage, most students quickly learn a programming language such as LabVIEW. The graphical, or icon-based, LabVIEW approach to programming is an effective way for students to learn data acquisition, measurement, and fundamental signal processing.

With the graphical display of FFTs in real time using LabVIEW, the students explored and viewed the dynamic changes as the time series data inputs were changed. The traditional method of classroom teaching DSP using mathematical equations would have made visualization almost too difficult for the students to understand and appreciate. With this hands-on approach, students learned more about the fundamentals of DSP and data acquisition.

For more information, contact:
Alex See, PhD
Monash University Malaysia, School of Engineering and Science
No. 2 Jalan Kolej, Bandar Sunway, 46150, PJ
Selangor Darul Ehsan
Malaysia
Tel: (+60) 03 5636 0600 Ext: 3202
Fax: (+60) 03 5632 9314
E-mail: alex.see@engsci.monash.edu.my

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