Web-Based Laboratory for Temperature Control Frequency Response Analysis
"The original experiment hardware consists of a
process trainer, a function generator, and an
oscilloscope. The prototype eliminates the function
generator and the oscilloscope, significantly
reducing the total cost. We replaced the function
generator and oscilloscope with LabVIEW software
to simulate input signals and display output signals."
- Rohaiza Binte Baharudin, Universiti Teknologi MARA
The Challenge:
Developing a cost-effective, hands-on laboratory for actual experimentation to teach highly theoretical abstract engineering concepts.
The Solution:
Using NI LabVIEW software, the NI Educational Laboratory Virtual Instrumentation Suite (NI ELVIS), and NI DAQ hardware to design and implement
a remote laboratory to teach control system theory to enhance the conventional teaching method and optimize available resources.
Author(s):
Rohaiza Binte Baharudin - Universiti Teknologi MARA
Iza Sazanita Isa - Universiti Teknologi MARA
Afaf Rozan Radzol - Universiti Teknologi MARA
Norhazimi Hamzah - Universiti Teknologi MARA
As part of an engineering education, a control system course is highly theoretical and contains abstract concepts that require practical sessions to ensure
understanding. However, hands-on laboratories have huge drawbacks in terms of the high cost associated with the required equipment, space, and
maintenance.
We designed and implemented a remote laboratory to teach control system theory to electrical engineering students at the Universiti Teknologi MARA. We
chose frequency response analysis as the initial prototype to enhance the curriculum and optimize available resources.
System Setup
The experiment setup used an open-loop frequency response concept (see Figure 1). The output voltage (Vo) of a linear system to a sinusoidal input
voltage (Vi) was a sinusoid of the same frequency but with a different magnitude and phase.
The original experiment hardware consisted of a process trainer (FEEDBACK PT 37-100), a function generator, and an oscilloscope. The prototype
eliminated the function generator and the oscilloscope, significantly reducing the total cost. We replaced the function generator and oscilloscope with
LabVIEW (http://www.ni.com/labview/) software to simulate input signals and display output signals. For communication between the host PC running
LabVIEW software and the process trainer, we used an NI ELVIS (http://www.ni.com/nielvis/)DAQ module (see Figure 2).
We used NI ELVIS with two analog output ports and eight differential or 16 single-ended analog input ports. The system sent the input signal generated by
LabVIEW to the process control trainer through the DAQ analog output channel. The system sent the process control trainer output to the host PC through
the DAQ analog input channel (see Figure 3).
Prior to conducting the remote experiment, we gave the students a pre-test. The questions were related to frequency response theories to ensure that the
students were equipped with the required knowledge. Students who passed the pre-test then proceeded with the remote experiment. We prepared an
experiment manual to assist the students with the procedures. Upon completion of the experiment, the students filled out an evaluation to measure the
effectiveness and user satisfaction of the system.
Results and Advantages of Web-Based Experiments
We successfully designed our remote lab prototype for frequency response of a temperature control system experiment to complement the control system
course offered to electrical engineering students. Using the prototype setup, the remote user requested connection from the host PC. After establishing
connection, the remote user viewed the VI front panel through an HTML window (see figures 4 and 5).
The front panel showed the input and output waveforms of the system. From the graph, the students observed that the output of frequency response was
a sine wave with different amplitude and phase. The students varied the input signal frequency and measured the magnitude and phase of the frequency
response. By varying the frequency, students observed that the amplitude and the phase of the output waveform also varied. The students used the
obtained measurement to manually plot the system Bode diagram. Numeric indicators displayed the required measurements for sketching the system
Bode diagram such as magnitude (dB), phase (deg), and frequency (rad/sec) on the front panel.
This web-based experiment offered a few advantages. Remotely conducting the experiment significantly reduced experiment time from one hour with a
conventional hands-on laboratory to just 30 minutes because the students did not need to set up the experiment equipment before taking the
measurement. Therefore, more students could access and conduct the experiment within the specified lab period. In addition, this web-based experiment
reduced the cost required to develop the experiment setup by replacing the function generator and oscilloscope with PCs. Only the host PC ran the
LabVIEW software, which reduced the cost of a traditional system by up to 45 percent.
The most significant advantage of a web-based lab is its flexibility in terms of facilities use because remote users can access the host PC from anywhere
in the local area network (LAN). It requires a small space to set up the host PC and the experiment equipment. This means that other courses can use the
current lab, further reducing the space congestion problem in our department. The technician turns on the host PC and sets up the experiment at a
specific allocated time for the remote users. The users can choose to run the experiment from a remote PC during the allocated time from anywhere within
the LAN for time flexibility compared to the conventional hands-on lab.
System Study
To verify the functionality of the system, we conducted a comparative study that evaluated the measurement accuracy between the remote and
conventional lab. The system obtained a measurement from the remote lab, which showed a significant difference from the conventional lab
measurement, especially for the phase difference measurement (see Table 1). The difference might be due to the delay in transferring data from the
equipment to the PC through the DAQ module and vice versa. However, for both techniques, the magnitude and phase difference measurement exhibited
decreasing trends, which are important in sketching a Bode diagram and describing the system stability.
Conclusion
We created a remote laboratory for a frequency response experiment using LabVIEW, NI ELVIS, and DAQ. Students can remotely access the experiment
and interact with the actual experiment setup through the web. They can graphically measure and display the input/output response of the system on a
remote PC. The measurements obtained do not give satisfactory results in term of accuracy, but the decreasing measurement trend for both readings is
sufficient to explain the Bode diagram concept, which is the main objective of the experiment. We developed the system within the available resources and
significantly reduced the cost and time it took to conduct the experiment.
Author Information:
Rohaiza Binte Baharudin
Universiti Teknologi MARA
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Fakulti Kejuruteraan Elektrik, UiTM Cawangan Pulau Pinang, Permatang Pauh
13500
Malaysia
Tel: 604-3823348
Fax: 604-3822819
rohaiza684@ppinang.uitm.edu.my (mailto:rohaiza684@ppinang.uitm.edu.my)
Figure 1. Temperature Control Systems Block Diagram
Figure 2. Remote Structure
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Figure 3. Prototype Operation Flowchart
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Figure 4. Front Panel of Frequency Response
Figure 5. Block Diagram of Frequency Response
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Figure 5. Block Diagram of Frequency Response
Table 1. Measurement Evaluation
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