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User-defined Electrical Experiments ina Remote Laboratory Session 2359


Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition
Copyright
©
2003, American Society for Engineering Education
User-defined Electrical Experiments in a Remote Laboratory


Ingvar Gustavsson

Department of Telecommunications and Signal Processing
Blekinge Institute of Technology, Sweden




Abstract

Laboratory exercises in electrical engineering courses can be performed remotely using real
equipment. A number of user-defined experiments on electrical circuits have been conducted
over the Internet at Blekinge Institute of Technology (BTH), Sweden; the experiments have been
carried out in different locations simultaneously using the same experimental hardware located in
a small closed laboratory at BTH.

The laboratory provides a remotely controlled switch matrix, two function generators, a digital
multi-meter, and an oscilloscope. The matrix replaces the traditional breadboard and students and
other users around the globe use it to form circuits from components mounted in component
holders in the matrix. It has five nodes; a jumper lead or up to four components can be connected
between each pair of nodes. The laboratory supervisor or a teacher can easily swap components.
Users control the instruments using virtual front panels in the same way as they had done earlier
in the local laboratory; the only difference is that they no longer form the circuits and connect the
test probes manually.

Circuits are defined using PSpice compatible net lists. The sources and components available in
the laboratory are listed in a library. This library can be added to the libraries in, for example, the
evaluation version of PSpice. Students can, within certain limits, modify the circuits shown in
the laboratory instruction manuals or even design circuits of their own. A virtual laboratory
instructor checks the circuits formed automatically before the voltage is applied to avoid possible
damage.

Is it possible to establish a reasonable balance between the teachers needs and the complexity of
the hardware? Can the virtual instructor check the circuits formed without making advanced
calculations or simulations? This paper addresses these questions and discusses implementation
issues.

Introduction

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Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition
Copyright
©
2003, American Society for Engineering Education
It is well-known that real experiments are indispensable in engineering education as a means of
developing skills for dealing with physical processes and instrumentation. The traditional way of
conducting experiments is to go to a university laboratory where students work in teams and
receive tutorial help from teachers. Models for using information technology to enhance the
learning experience for students who are asynchronous in time or/and space and which are also
suitable for on-campus students have been presented earlier
1,2
. A number of so-called remote
laboratories have been set up by some universities around the world. These offer remote access
to laboratory equipment and experimental setups
3
.

Laboratory exercises are run in the remote laboratory for undergraduate education in electrical
engineering at Blekinge Institute of Technology (BTH)
4
. A number of people located in different
places around the globe can perform experiments simultaneously using client PCs connected to a
laboratory server via the Internet. They download the client software from the laboratory web
site. This is one way to use the equipment and premises efficiently. The cost of the equipment
and its maintenance can be cut down if the number of lab stations is reduced and/or the
laboratory is used outside ordinary working hours.

Another purpose of the remote laboratory at BTH is to provide exercises which are almost
identical to conventional ones. In fact, the exercises in the remote laboratory could also be
performed in the traditional manner. The same laboratory instruction manuals will serve the
purpose. Conventional laboratory exercises have been used with success to teach science and
engineering for many decades. To try to copy these exercises might be a good starting point from
which new teaching methods could emerge.

In a traditional laboratory the students can perform experiments of their own using the equipment
and components available. In the remote laboratory at BTH it is only possible to form predefined
circuits using the laboratory servers described earlier. This paper focuses on user-defined
experiments made possible by a new laboratory server. First the traditional method of doing
laboratory exercises will be examined and then the remote version will be described.

Traditional laboratory exercises are a successful teaching method

In a traditional undergraduate electronics laboratory at BTH eight identical lab stations are
available. At each station there is a lab box with a white plastic breadboard which is detachable
and some desk top instruments as shown in Figure 1. An instructor provides the components
necessary for each laboratory session. Every exercise is described in an instruction manual. The
normal procedure for performing a single experiment is as follows:
1. The student forms the circuit specified in the laboratory instruction manual using the
breadboard and some of the components provided. The instruments are connected to test
points.
2. The instructor checks the circuit formed to avoid possible damage. If the circuit is
harmless the student is allowed to go on and activate the voltage source.
3. The student reads the instruments and evaluates the results. If they are acceptable s/he
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Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition
Copyright
©
2003, American Society for Engineering Education
enters them in a laboratory report. Where this is not the case, some troubleshooting must
be carried out, if necessary, with the support of the instructor.


Figure 1: A traditional lab station in a laboratory for undergraduate education in electrical
engineering at BTH.

Remote experiments add a new flexibility
The new laboratory server at BTH is shown in Figure 2. To the left there is a PXI (PCI
Extensions for Instrumentation) chassis (PXI-1000B) containing a controller (PXI-8176) and
four plug-in boards from National Instruments. The controller comprises a PC connected to the
Internet which hosts the plug-in boards in the form of two function generators (PXI-5411 and
PXI-5401), an oscilloscope (PXI-5112) and a digital I/O board (PXI-6508). The instrument
settings are controlled from the host computer and there are no buttons or control knobs on the
generators or the oscilloscope, only connectors. Next to the PXI chassis is a Data
Acquisition/Switch Unit (Agilent 34970A, 34901A, 34903A, and 34904A) which functions as a
multi-meter; this is connected to the controller via the GPIB (General Purpose Instrument Bus).
To the right is a power supply (HP E3631A). The server software is written in LabVIEW 6.1
(Laboratory Virtual Instrument Engineering Workbench)
5
.
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Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition
Copyright
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2003, American Society for Engineering Education


Figure 2: A laboratory server for experiments in circuit theory and basic electronics.

A small remote laboratory which provides a virtual breadboard with four nodes using a relay
switching matrix has been presented earlier
6
. It provides two sources and three resistors. Would
it be possible to replace the traditional breadboard by a remotely controlled switch matrix large
enough to accommodate most of the circuits used in electrical and basic electronic experiments
in undergraduate education? The matrix used in the remote laboratory at BTH has five main
nodes and ten main branches, Figure 3. The main nodes are denoted A, B, C, D and GND. The
ground terminals of the function generators and the oscilloscope are connected to GND. Each
main branch can be composed of a jumper lead or up to four components with two leads
mounted in parallel in holders on the printed circuit boards shown in Figure 2. In this way a total
of 40 different components can be connected. All connections to node A are shown in Figure 4.
To support components with more than two leads such as transistors or operational amplifiers an
additional printed circuit board and some software modifications are required. The laboratory
supervisor or the teacher can easily swap components. The switches used to connect the
components are mounted near the component holders on the printed circuit boards. The server
controls these switches using the digital I/O board in the PXI chassis. The switches in the Data
Acquisiti