The University of Virginia Uses NI LabVIEW and DAQ in Undergraduate Electrical and Computer Engineering Power Laboratories

Author(s):
Harry Powell - The University of Virginia

Industry:
University/Education

Products:
LabVIEW, Data Acquisition

The Challenge:
Creating an educational program for teaching power system concepts to undergraduate engineering students.

The Solution:
Using National Instruments software and hardware to create curriculum, laboratory experiments and in-class demonstrations in a user-friendly environment.

In the Spring of 2006, the University of Virginia developed software and hardware programs designed to help student instruction in Electromagnetic Power Conversion classes. The department also installed a new computerized laboratory for students. National Instruments LabVIEW software and DAQ hardware was used to develop custom applications for class and laboratory use.

The new hardware and affiliated LabVIEW software was used by all power lab experiments in which measurements were taken at line voltages and frequencies. Connections are available for three phases each for voltage and current, and one each for DC voltage and current. Current transformers are used for the AC current connections, which results in “lossless” and isolated conversions of current voltage. All inputs are isolated from each other and floating, which allows complete freedom in connection schemes. Each input may be essentially treated as a separate discrete input without regard to a particular ground or neutral.

The DC Current input is also isolated and lossless. It employs a DC closed loop GMR sensor, Model CMR-25 from FW Bell. This sensor develops an isolated differential voltage output using a GMR sensor, similar to a Hall-Effect device. The device has local power supply regulation via the LM7805 regulator, and is supplied buy a conventional wall-cube power supply. Conversion ratio is 0 to 8.3 amps DC, ranged to 0 to 5 volts DC.

All software used in the laboratory experiments is written using LabVIEW. Interface to the NI hardware is via an NI DAQ-MX. As much as possible, common user interface schemes were used for all programs.

An interesting feature for this block diagram developed for the front panle, from an educational standpoint, is the similar layout of the front panel to one used for an in-class power factor demonstration. Also, the average power was calculated in the same fashion and the instantaneous power was shown as well. Students were somewhat “shocked” to discover that the real signals, in this case, behaved exactly like the simulated version, and that the math did indeed work; the block diagram includes the same multiplication and filtering sub-VIs as the simulated version.

This indeed is a great benefit in using LabVIEW for instructional purposes. Simulated signals may be used for lecture purposes; real signals are used in the actual laboratory measurements.

Similar software was written for each explicit laboratory session, with the features made possible. One interesting application was the measurement of B_H Curves for a typical transformer core. By application of VIs to perform numerical integration, the concepts behind Faraday’s Laws, and the hysteretic nature of a magnetic core were clearly seen in the laboratory. In the past, using conventional oscilloscope instrumentation, the obtainable signals were very weak and noisy due, in part, to isolation issues. The computerized instrumentation circumvents this problem, and allows the underlying concepts to be emphasized.

A combination of in-class demonstrations, simulations and computerized data acquisition for laboratory use has proven to be an effective route for conveying power systems concepts. We have observed that students who have a genuine interest in the course have taken extra time on occasion to extend the experiments on their own, and the user-friendly data-gathering environment has facilitated this. I believe that this equipment has been a wise investment for the engineering school, and I hope that it may be expanded upon for classes in the future.

Author Information:
For more information on this Case Study, contact:
Harry Powell
The University of Virginia
hcp7ad@virginia.edu

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