Electronic filter

Sample times for the microprocessor-based SLCs vaiy from O.I to 0.4 seconds. Low-pass analog electronic filters are installed on the process inputs to stop abasing errors caused by fast changes in the process signal. Input filter time constants are typically in the range From O.I to I s. Microprocessor-based SLCs may be made part of a DCS by using the communication port (RS-488 is common) on the controller or may be operated in a standalone mode independent of the DCS. 

Electronic filter A filter incorporating an electrostatic precipitator. A fibrous filter that has its collection efficiency electrostatically enhanced. 

In many instances the quality of the signal has to be improved before the chemical information can be derived from it. One of the possible improvements is the reduction of the noise. In principle there are two options, the enhancement of the analog signal by electronic devices (hardware), e.g. an electronic filter, and the... 

The exponential shape of the filter follows directly by elaborating eq. (40.14) for a few consecutive data points (see Table 40.4). From this table we can see that a smoothed data point at time i is the average of all data points measured before, weighted with an exponentially decaying weight X< ) with d the distance of that data point from the measurement to be smoothed. Such shapes are also found for electronic filters with a given time constant. The effect of exponential smoothing is visualized in the plot of the a , and values (Fig. 40.25) listed in... 

In applying RAIRS to CO adsorption, the contribution from CO molecules in the gas phase to the absorption spectrum at CO pressures above 10-3 mbar completely obscures the weak absorption signal of surface adsorbed CO. Beitel et al. found it possible to subtract out the gas phase absorption by coding the surface absorption signal by means of the polarization modulation (PM) technique applied to a conventional RAIRS spectrometer, p-polarised light produces a net surface electric field which can interact with adsorbed molecules, whereas both polarization states are equally sensitive to gas phase absorption because gas phase molecules are randomly oriented. By electronic filtering a differential spectrum is computed which does not show contributions from the gas phase and which has much higher surface sensitivity than a conventional RAIRS setup. 

Figure 11.10. Phase-locked detection of fluorescence lifetime using single reference signal. FID = fluorescence inducing and detecting devices LPF = low-pass electronic filter VCO = voltage-controlled oscillator v, = signal to modulate the output intensity of the excitation light source v/= the fluorescence signal.

Chlorpyrifos Data Set (Flame Photometric Data) Phosphorus mode with no electronic filtering. 

Clicking with the right mouse button on the FT button opens a dialog box for activating and performing a 5th order phase correction, together with the FT. This automatically corrects non-linear phase distorsion in the spectrum, introduced by electronic filters. With the available data this correction is not necessary and its application produces no effects in the final spectrum. 

The first second of a stress relaxation step can also show this type of ringing, but it is generally caused by the transducer itself. Thus, the first part of the data may be electronically filtered to remove the transducer ringing by setting a filter cutoff frequency of -40% of the value for the resonant frequency of the transducer and geometry. Some rheometers allow for the measurement of transducer resonant frequency when measuring the geometry inertia. 

The negative peak in the baseline at 4520 cm-1 proved to be a convenient reference position. Its origin is presently unknown, but it likely arises from slight differences between the silica DIT cell used for the sample and that used for the carbon tetrachloride reference. Band integration did not work veil for quantitation in this study, probably because of uncertainties in the data above 5264 cm-1 where the discontinuity due to the electronic filter in the spectrometer occurs. 

This technique can be even applied if the conditions (ii), (iii), and (iv) are not observed. In the latter case, however, regression analysis of the I-U dependencies requires to define explicit relationships between chemical potentials of all components, their concentrations, and mobilities. In practice, experimental problems are often observed due to leakages, non-negligible -> polarization of reversible electrodes, indefinite contact area between solid electrolyte and electronic filter, formation of depletion layers and/or phase decomposition of the electrolyte. 

Also, conductimetric detection has been used, by applying two electrodes into the capillary. In this detection mode, the separation of the high voltage part of the capillary (under dc) from the detection zone (under ac) can be accomplished also by electronic filtering. A capillary electropherograph, with a conductimetric detector, is commercially available. 

At the high-sensitivity-range settings of some detectors, electronic 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. 

A phase difference between the carrier frequency and the pulse leads to a phase shift which is almost the same for all resonance frequencies (u)). This effect is compensated for by the so-called zero-order phase correction, which produces a linear combination of the real and imaginary parts in the above equation with p = po- The finite length of the excitation pulse and the unavoidable delay before the start of the acquisition (dead time delay) leads to a phase error varying linearly with frequency. This effect can be compensated for by the frequency-dependent, first-order phase correction p = Po + Pi((o - (Oo), where the factor p is frequency dependent. Electronic filters may also lead to phase errors which are also almost linearly frequency-dependent. 

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