Signal pre-processing

Jemielniak K (2001) Some aspects of acoustic emission signal pre-processing. J Mater Process Technol 109 242-247... 

D. Miller, D.Placko "Pre-processing of signals delivered by a new eddy current sensor for non ferromagnetic tubes testing" in IMTC 96... 

The magnetic scan is synchronised with the x-axis of a recorder and calibrated to appear as mass number (strictly m/e). The amplified current from the ion collector gives the relative abundance of ions on the y-axis. The signals are usually pre-processed by a computer that assigns a relative abundance of 100% to the strongest peak (base peak). 

More precisely, die quantity displayed is the signal power estimated from 10ms frames. As die power spectral densities of die two types of noise exhibit a strong peak at the null frequency, the two noises were pre-whitened by use of an all-pole filter [Cappe, 1991]. This pre-processing guarantees that the noise autocorrelation functions decay sufficiently fast to obtain a robust power estimate even with short frame durations [Kay, 1993]. 

A number of approaches may be employed to process the grey image into digital signals in order to obtain a more useful result. Pre-processing may include ... 

The various stages in the signal processing of an electronic nose system are illustrated in Figure 11 in which the signals generated from an array of sensors (or, for example, pseudo-sensors in a mass spectrometer) are first pre-processed and then fed in to a pattern analyser. In other words the n dimension vector in sensor space is transformed into feature space (a process called feature extraction) and then identified using some form of pattern classifier. 

Table 7. Some different pre-processing algorithms used to generate static parameters Xy-, frequency if), resistance R), conductance (G), signal (s), baseline (0), sensor (i), odour (j).

The raw array data acquired in GenePix Pro have to be pre-processed to separate signals from noise, eliminate low-quality measurements, handle missing values, and adjust the measured intensities to facilitate comparisons (12,13). Image analysis tools reduce the background signal and minimize the impact of poor-quality spots on the final array data (11,12). 

Collection, pre-processing and displaying of measured data and control signals... 

The operation of ECCS pumps is also possible from a local key lock hand switch and from the control room but automatic signals pre-empt all others. In the event of normal power failure while the system is operating or in the process of going into operation, the system will restart from the standby sources. All system alarms annunciate in the control room. 

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