Complete course notes

Pagina 1

SAMPLING Introduction The focus of the course will be not the instrumentation sites, but the understanding of complex signals, we'll see algorithms and techniques to extract information from signals. First of all, we must study how the acquisition of data works. Acquisition of data (or sampling): introduction In general, we want to transform the information that we are measuring (like the temperature, for example) into a voltage signal because it's easier to carry the signal far apart from where the measurement takes place and so it’s easier to collect all the dat a. Usually, we would like to obtain a linear relationship between t he physical phenomenon and the output signal. Let’s imagine having a plot that represents all the data that we have collected as the one depicted in the picture. From this plot we can extract some information like, for example, the maximum value or the minimum value, but we are not able to obtain other parameters like the average due to the fact that we have a continues measurement that is not a function. In case of a function we would be able to compute the average since it is defined as the ratio b etween the integral of the function itself and the intervals: 𝑎𝑣𝑎𝑟𝑎𝑔𝑒= ∫ 𝑓(𝑡) 𝑇 So, we have understood that one of the main problems is the fact that we are dealing with a continuous measurement and not a function. Another important element to consider is trying to understand how we should choose the time interval: this choice is up to us and it depends on what we think is meaningful. Depending on how many time intervals we choose we could increase or decrease the resolution 1 of our measurement that can be defined as the minimum variation in the input that causes a variation of the output, in other words it is the minimum variation that causes a…