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Unformatted text preview: 1 W. E. Dunn ME 360: FUNDAMENTALS OF SIGNAL PROCESSING, INSTRUMENTATION AND CONTROL Laboratory No. 2 Signal Conditioning and Analog-to-digital Signal Conversion Issues 1. CREDITS Originated: N. R. Miller, July 1997 Last Updated: D. Block, September 2009 2. OBJECTIVES (a) Become familiar with the PC-based signal conversion hardware and software available in the laboratory. (b) Study the problems of aliasing and quantization error associated with the digital representation of analog signals. (c) Demonstrate the noise attenuation techniques of filtering and integration. 3. KEY CONCEPTS (a) Information is irreversibly lost when an analog signal is converted to digital form. The loss is minimized by sampling at a high rate and using a high-resolution digital representation. (b) A digitized sine wave appears to be a sine wave at a lower frequency if the sampling rate is less than twice the frequency. This effect, known as aliasing, distorts the frequency spectrum of any signal by mapping higher frequency components into lower frequency components. (c) Aliasing cannot be detected by examining the digitized signal alone. (d) Thermocouples measure temperature by producing millivolt-level signals. The leads of a thermocouple act as an antenna to pick up electrical noise from the environment. The amplitude of this noise can cause problems when measuring the output of the thermocouple. 4. SYNOPSIS OF PROCEDURE (a) Observe the effect of aliasing using the function generator, oscilloscope, audio earphones, PC-based data acquisition hardware, and MATLAB software. (b) Observe quantization error in a ramp function using the PC-based digital-to-analog conversion hardware. (c) Investigate the use of a simple, RC, low-pass filter to attenuate high-frequency noise. (d) Measure the output of a Type-T thermocouple using the digital multimeter. 5. PROCEDURE The procedure is presented at three levels of detail. The lowest level of detail is set forth in the synopsis above and the headings of this section. Review this information first to get a good intuitive feel for the overall scope of the experiment. The second level of detail is a brief description of each specific task often accompanied by a schematic or sketch. This description together with the Data Sheet is usually sufficient to understand and carry out the procedure during the laboratory session. The first two levels of the procedure described above should be thoroughly reviewed before coming to the laboratory. Skip over the detailed procedure in preparing for the laboratory session as this information only makes sense when the equipment is at hand. Important General Information – Please Read Carefully (a) Always turn off the power supplies when changing connections. Dangling leads can easily contact the metal tabletop creating a short, blowing a fuse, creating an unsafe situation or damaging the equipment....
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This note was uploaded on 04/18/2010 for the course ME 360 taught by Professor Staff during the Spring '08 term at University of Illinois, Urbana Champaign.
- Spring '08