tailieunhanh - Advances in Measurement Systems Part 7

Tham khảo tài liệu 'advances in measurement systems part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 236 Advances in Measurement Systems Distortion of the signal caused by non-perfect dynamic response of the measurement system makes the determination of the time delay ambiguous. The interpretation of dynamic error influences the deduced time delay. A joint definition of the dynamic error and time delay is thus required. The measured signal can for instance be translated in time the delay to minimize the difference the error signal to the quantity that is measured. The error signal may be condensed with a norm to form a scalar dynamic error. Different norms will result in different dynamic errors as well as time delays. As the error signal is determined by the measurement system it can be determined from the characterization section or the identified model section and the measured signal. The norm for the dynamic error should be governed by the measurand. Often it is most interesting to identify an event of limited duration in time where the signal attains its maximum changes most rapidly and hence has the largest dynamic error. The largest L norm relative deviation in the time domain is then a relevant measure. To achieve unit static amplification normalize the dynamic response y t of the measurement system to the excitation x t e B . A time delay T and a relative dynamic error s can then be defined jointly as Hessling 2006 s f min T max x t eB t H - x t -t maxjj x t k t 7 1 r --- f f m B a dm af B0 SH í t H 0 w ữB J l r fdf 0 8 1 s m n k B7 The error signal in the time domain is expressed in terms of an error frequency response function SH ia T H t - exp iar - H o related to the transfer function H of the measurement system. The expression applies to both continuous time ơ irn as well as discrete time systems ct exp ia Ts Ts being the sampling time interval . It is advanced in time to adjust for the time delay in order to give the least dynamic error. The average is taken over the approximated magnitude of the input signal spectrum normalized to one B o 1