Design of passive artificial load using NI modules

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Dr. Sujbert László
Department of Measurement and Information Systems

This Bachelor Thesis Project presents the details of the design of a passive artificial load. My task was to design the hardwere and the controller software of the device too.

In the work’s first phase I, and the engineer group of the National Instruments defined the most important specification of the project. Within the confines of the specification we set the input voltage to a range of U = 0-30 V and we set the interval of the loading current between I = 0-2 A and also we expect a current resolution of I = 100 mA in the interval.

I made a system design based on the specification. I designed the resistor structure, that could be adjusted from 0.1-111 Ω by steps of 0.1 Ω. This resolution guarantees that the expected loading current can be set.

I selected the components in the design’s next step. I made calculations about the dissipation of the resistors, I chose them and I provided the appropriate cooling for them. I chose the relays, and by controlling them I can set the resultant resistance of the system. I provided the drive of the relays too. I selected the control unit of the system and I designed the measurement of the input voltage and the loading current. Throughout the hardware design I analyzed the errors, which can influence the accuracy of the measurements and I made calculation in reference to them.

After the hardware design I built the device on a board. I optimized the placement of the components in order to the signal and power lines do not cross each other and I attempted to minimize the length of the cables. After I fixed all of the components on the board, I tested the system in many ways and I fixed up the wrong connections what I caused during the slice.

The next step was to design the control program in LabVIEW. The front panel of the software allows of the control of every relay independently of each other during the program runs. I also made the measurements of the input voltage and the loading current.

During the calibration I came to know that the hardver works the way I wanted when I designed it. The errors show up, but the range of them is as small as I expected.

To sum up it could be said, that the initial goals were reached, because the result is such a device, that provides 1% accurate loading current in the whole predetermined range.


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