280 11 Sampling aid Periodic Sigiials Figure 11.20: Sampling a signal in the real-world A diagrammatic tlrscription of tlris sampling procedure is showii irr Fig11.21 Coinpared to the ideal sarriplirig in Figure 11.6, there is an additional systrrn with impulsc response h ( t ) = Lrect(L) UI‘C r I’ipure 11.21 Non-idcal sarnpling of t h e signals 2(t) The dcscription of non-idcal sitinpliiig introcluced here with the c~xaiiiplcof an clcctricd sigrial also applies to other signals h i cvcry case, iiieasurerrierit of a signal value requires c2 certain time A fiir t t w r generalisation is the assumption that the enrrgy transfer ih not Luiiforni within thc tirnc z Wt can take this iiito accwurit insing any weighting function U ( t ) with T n ( t ) > for - - < t < 2 a ( t ) = otherwise (11.47) instead of t,hc Tcctangle fimction Before the intcgration, i ( v )in (11.45) is iiiidtiplied by t r ( t - U) In connection with optics, u ( t ) is also callcd an aprrtuw f u r r c t x m