Filtering noise

Short Term Noise consists of base line perturbations that have a frequency that is significantly higher than the eluted peak. Short term detector noise is not often a serious problem m liquid chromatography as it can be easily removed by an appropriate noise filter without affecting the profiles of the peaks. Its source is usually electronic, originating from either the detector sensor system or the amplifier. 

Figure 9. Phase reconstruction of image reported in Figure 6 using the reference of image reported in Figure 8. The phase map is shown in (a), which includes a laterally averaged line-scan of 15 pixels, (b) A surface map of the two particles shape is displayed. The surface plot has been heavily noise filtered through Gaussian smoothing to better display the particles shape.

In this case we assume the disturbance term, e , is not white noise, rather it is related to through the following transfer function (noise filter)... 

The Dephy data-processing package offers several proprietary noise filtering options. We have not yet determined unequivocally whether any of these data treatments increase reproducibility or concentrate the taxonomic information content of the averaged spectra, although first results suggest that use of filtered data can improve spectral reproducibility and thus assist the ruggedness of sample classification. 

These techniques offer even more interesting noise-filtering properties as they are capable of localizing time- and frequency-varying noise and signal components. 

The rest of the detector signal is noise filtered and amplified by a lock-in amplifier. The output of the lock-in amplifier is monitored by an oscilloscope, and recorded as the laser scans across the gas s absorption line. The result is a spectral profile of the gas absorption, impressed on the depth of the locked resonance dip. This is then analyzed using (5.6) to find an experimental effective absorption path length. 

For this method, the first derivative of the temperature has to be determined from process measurements with amplified noise filtered out. Since the "safe" temperature need not be specified, the independence and selectivity of this method is greater than with the temperature criterion alone. Another advantage is that a potentially unsafe condition can be identified in its early development stage. However, a number of frequently used, but low hazard thermal processes are characterized by fairly high heating rates, making the use of the first derivative ineffective. 

Figure 5.12 shows both the dynamic and the static model deformation densities in the plane of the oxalic acid molecule, based on the data set also used for Fig. 5.2. The increase in peak height, due to higher resolution, and reduction in background noise relative to the earlier maps is evident. The model acts as a noise filter because the noise is generally not fitted by the model functions during the minimalization procedure.

Wayman and Wilson, 1988] Wayman, J. and Wilson, D. (1988). Some improvements on the synchronized-overlap-add method of time scale modification for use in realtime speech compression and noise filtering. IEEE Trans. Acoust., Speech, Signal Processing, 36(1) 139-140. 

Kasparis and Lane, 1993] Kasparis, T. and Lane, J. (1993). Adaptive scratch noise filtering. IEEE Trans. Consumer Electronics, 39(4). 

Typically, compression and filtering of spectroscopic data go hand-in-hand. Often, the process of compressing the data leads to a certain amount of noise filtering. 

It also specifies the level of signal that is observed. d This specifies the frequency response of the system and is accompanied by a time requirement. More noise filtering requires a long measurement. e Most commercial burners do not use a sheath gas however, there is always the possibility of a sheath gas in EAAS. f This is important if the sample solution flow rate is controlled by a pump rather than by the oxidant gas flow rate. 

FIGURE 3.18 HRTEM image of PFA-P7-H carbons. An inset is a corresponding electron diffraction pattern. The image just below the electron diffraction pattern is a noise-filtered image taken from the area indicated by a square. 

Data acquisition is straightforward, while digital noise filtering can improve long-time data [87]... 

If should be nofed that at the high sensitivity range settings of some detectors, filter circuits are automatically introduced to reduce the noise. Under such circumstances the noise level should be determined at the lowest attenuation (or highest amplification) that does not include noise-filtering devices (or at best the lowest attenuation with the fastest response time) and then corrected to an attenuation of unity. 

Sensor type and location, as well transmitter characteristics, noise, and sampled data issues, also can affect loop performance. Most continuous measurement sensors and transmitters have relatively fast dynamics and a noise filter, which can be approximated by a... 

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