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Digital Signal Processing
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Digital Signal Processing |
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Throughput Rates of Digital
Systems
The electrical resistance strain gage is an inherently analog device that utilizes changes in the relative resistance of the gage to quantify mechanical strains in the surface to which it is attached. Of course, as readers probably already know, the strain gage is typically connected to some form of instrumentation that incorporates a Wheatstone bridge circuit to provide an analog electrical signal that varies as the strain changes. Indeed, most sensors -- whether they be strain-gage-based transducers, LVDT's, thermocouples, piezoelectric devices, or a wide variety of others -- ultimately produce such a signal. Unfortunately, the digital computers increasingly incorporated into measurement systems are inherently incompatible with these analog signals. To store measurement data in digital form, the analog signal must be sampled at various points in time and converted to numbers, i.e., the signal must be digitized. Ideally, the time between samples should be vanishingly small (approaching zero). But we know from arithmetic that anything divided by zero is infinitely large. And, of course, the computer can only handle a finite number of data points. The question then becomes how infrequently to sample. If the signal is oscillating on a regular basis, then a minimum of ten data points per period, for the highest frequency component to reasonably reconstruct the signal in the time domain, are required. In the frequency domain, any rate of more than two samples per period will suffice. In order for these conditions to be met, a digital measurement system must have a sufficient throughput rate. (continued...) 
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