Recorder time constant

With cw, the increase of the recording time constant is not as efficient as expected because the low-frequency components of the noise are stronger and the reduction of the sweep speed increases line saturation. But with digital memory oscilloscopes and computers it is now possible to repeat the sweeps and average the different recordings. The improvement on a given line is obvious. The experiment is relatively easy to set up and it has been used for Stark effect studies 14).But the stability and reproducibility needed in the search of new lines, with broader sweeps, make this technique somewhat difficult to use and no suclt experiment seems so far to have been reported for nitrogen. 

In MWD, the recording speed is the rate of penetration which rarely exceeds 120 to 150 ft/hr or 2 to 2.5 ft/min, two orders of magnitude less than the logging speed. Counters can be made shorter and time constant longer (up to 30 s or more). This results in a better accuracy and a better bed definition. Figure 4-269 shows an example of comparison between an MWD gamma ray log and the wireline log ran later. 

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

Fiq. 20a. The pulsed Raman spectrum of Mn-doped ZnSe single crystal using a detection interval of 200 nsec. Broad band fluorescence superimposed on a large instrumental scattered light component was observed. Recordings taken with ratemeter time constants (TC) of 1 sec and 10 sec are shown (37). 

For an ice sheet of thickness H in equilibrium with a climate supplying accumulation at a rate a (thickness of ice per imit time), the vertical velocity near the ice-sheet surface is a and this velocity decreases to zero at the ice-sheet bed. A characteristic time constant for the ice core is H/a. The longest histories are therefore obtained from the thick and dry interiors of the ice sheets (particularly central East Antarctica, where H/a = 2 X 10 yrs). Unfortunately, records from low a sites are also low resolution, so to obtain a high-resolution record a high a site must be used and duration sacrificed (examples are the Antarctic Peninsula (H/a = 10 ) and southern Greenland H/a = 5 x 10 )). 

As modern one- or two-dimensional detectors are used, every pixel of the detector is enforcedly receiving the same exposure (time). Only by means of an old-fashioned zero-dimensional detector the scattering curve can be scanned in such a manner that every pixel receives the same number of counts with the consequence that the statistical noise is constant at least in a linear plot of the SAXS curve. The cost of this procedure is a recording time of one day per scattering curve. 

The value of the calorimeter time constant r (= n), may be determined from the cooling curve which is recorded, for instance, when a Joule heating, which produced a constant deviation A0 of the base line (Fig. 11), is suddenly stopped (16). The comparison of Eqs. (14) and (15) shows that the cooling curve is represented by... 

Sometimes, to get data from 4 K up to room temperature, the simplest and more economical way is to let the cryostat warm if the thermal insulation is good and the vacuum chamber is kept under pumping, the warm-up time can be several days. If the experiment thermal time constant is much shorter, data at practically constant temperature can be recorded. 

In order to determine the thermal time constant of the microhotplate in dynamic measurements, a square-shape voltage pulse was applied to the heater. The pulse frequency was 5 Hz for uncoated and 2.5 Hz for coated membranes. The amplitude of the pulse was adjusted to produce a temperature rise of 50 °C. The temperature sensor was fed from a constant-current source, and the voltage drop across the temperature sensor was amplified with an operational amplifier. The dynamic response of the temperature sensor was recorded by an oscilloscope. The thermal time constant was calculated from these data with a curve fit using Eq. (3.29). As already mentioned in the context of Eq. (3.37), self-heating occurs with a resistive heater, so that the thermal time constant has to be determined during the cooHng cycle. 

Figure 14 illustrates a recorder curve of the resonance absorption derivative of F for a sample containing 2.7 wt. % of fluorine. The time of scanning the magnetic field through resonance was 2 hours and the time constant of the spectrometer was 90 seconds in order to increase the available signal-to-noise ratio. The F resonance absorption was examined in the concentration range of 0.3 to 12.5 wt. % fluorine. 

Experimental Analysis. The most reliable process measurement is the oscillator frequency from the PAAR densitometer. Along with the frequency, the temperature is also measured ( 0.05 C). These two states are used to interpolate the solute concentration. CSD weight percent information and obscuration measurements were obtained from the Malvern Particle Sizer. Approximately 500 concentration data points and 200 CSD and obscuration measurements were recorded during a run of about 80 -100 minutes. Therefore, the dynamics of the system were well monitored, i.e., the time constant of the crystallizer is much larger than the sampling time. We have performed 25 experimental runs. This section summarizes the analysis of a single, typical experiment. 

The effect of the detector time constant on the apparent efficiency depends only on the time width of the bands. It has been shown by Sch-mauch 41) and by Me William and Bolton 42) that the profile recorded with a detector having a time constant r is wider than the actual profile by a factor (1 -f r/ert), where is the time standard deviation of the profile, provided this factor is less than about 1.2. Moreover, the peak heigh becomes smaller although the peak area remains unchanged. 1 he (list mu ment (retention time) of a peak increases by r and the retention time of the... 

In most cases the time constant of the detector is due to slowness of the electronics this is especially true for optical detectoHi- There would be no technical problem to reduce the time constant tb 20-50 msec, although the noise level is expected to increase somewhan With such fast detectors computer data acquisition becomes necessary, as recorders with a time constant less than O.S sec are rare and expen ve. Since they are difficult to maintain, they are impractical. 

The contribution of slow detector response can be ne ected when the base peak width is at least 40 times larger than r [cf. Eq. 3)]. In practice it is difficult to correct for such distortion because the time constant concept is only an approximation. It is not very reproducible and is sensitive to changes in the characteristics of the various elemehts of the electronics. Furthermore, detectors, amplifiers, and record are not first-order systems mid their response is only iippruxinntted by an exponential function (44). The response time is therefore defined by the time neces-... 

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