Continuous wave systems

A problem with the early MWD mud pulse systems was the very slow rate of data transmission. Several minutes were needed to transmit one set of directional data. Anadrill working with a Mobil patent [100] developed in the early 1980s a continuous wave system with a much faster data rate. It became possible to transmit many more drilling data, and also to transmit logging data making LWD possible. Today, as many as 16 parameters can be transmitted in 16 s. The dream of the early pioneers has been more than fulfilled since azimuth, inclination, tool face, downhole weight-on-bit, downhole torque, shocks, caliper, resistivity, gamma ray, neutron, density, Pe, sonic and more can be transmitted in realtime to the rig floor and the main office. 

Figure 4-243. Telemetry systems using mud pressure waves (a) negative pulse system (b) positive pulse system (c) continuous wave system.

Figure 4-247. Principle of the continuous wave system (a) sketch of the siren and electronic block diagram (b) principle of the coding by phase shift keying. (Courtesy Anadrill [106].. ...

Figure 4-248. Example of a frame of data transmitted by the continuous wave system. (Courtesy Anadr/V [106] J...

Fig. 12.9 Time-Of-Flight system (TOF) (left) measures the time required for a laser pulse to travel to and return from an object. Continuous wave system (right) is a variation on the TOF method distance is computed by comparing the phase shift between an emitted wavelength and the received light [18]...

Much of the previous section dealt with two-level systems. Real molecules, however, are not two-level systems for many purposes there are only two electronic states that participate, but each of these electronic states has many states corresponding to different quantum levels for vibration and rotation. A coherent femtosecond pulse has a bandwidth which may span many vibrational levels when the pulse impinges on the molecule it excites a coherent superposition of all tliese vibrational states—a vibrational wavepacket. In this section we deal with excitation by one or two femtosecond optical pulses, as well as continuous wave excitation in section A 1.6.4 we will use the concepts developed here to understand nonlinear molecular electronic spectroscopy. 

Population inversion is difficult not only to achieve but also to maintain. Indeed, for many laser systems there is no method of pumping which will maintain a population inversion continuously. For such systems inversion can be brought about only by means of a pumping source which delivers short, high-energy pulses. The result is a pulsed laser as opposed to a continuous wave, or CW, laser which operates continuously. 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

The common liquid lasers utilize a flowing dye as the active medium and are pumped by a flash lamp or another laser. These are typically more complex systems requiring more maintenance. They can he operated as either CW (continuous wave) or pulsed. One advantage liquid lasers have is they can be tuned for different wavelengths over a 100-nm range. 

The first successful application of the continuous wave (CW) He-Ne gas laser as a Raman excitation source by Kogelnik and Porto (14) was reported in 1963. Since that time, significant improvements in instrumentation have been continually achieved which have circumvented a great number of problems encountered with mercury lamp sources. The renaissance of Raman spectroscopy has also been due to improvements in the design of monochromators and photoelectric recording systems. 

Numerical examples are shown in Figs. 7-9. The model system used is a 2D model of H2O in a continuous wave (CW) laser field of wavelength 515nm and intensity lO W/cm. The ground electronic state X and the first excited state A are considered. The bending and rotational motions are neglected for... 

High-frequency pressure oscillations (10-100 Hz) related to time required for pressure wave propagation in system Low-frequency oscillations (-1 Hz) related to transit time of a mass-continuity wave Occurs close to film boiling... 

So far, we have shown where the signal comes from, but how do we measure it There are two main technologies continuous wave (CW) and pulsed Fourier transform (FT). CW is the technology used in older systems and is becoming hard to find these days. (We only include it for the sake of historical context and because it is perhaps the easier technology to explain). FT systems offer many advantages over CW and they are used for all high field instruments. 

NMR spectra were obtained in continuous wave mode on a Varian T-60, and in the pulsed Fourier transform mode on a Varian HR-220 with Nicolet TT-100 Fourier transform accessory, a Nicolet NT-300 wide bore system, and a Bruker WM-500. 13C T1 data were obtained... 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

To meet all these system requirements specific waveform design techniques must be considered. For ACC systems both radar types of classical pulse waveform with ultra short pulse length (10 ns) or alternatively continuous wave (CW) transmit signal with a bandwidth of 150 MHz are considered. The main advantage of CW systems in comparison with classical pulse waveforms is the low measurement time and low computational complexity. 

Fourier transform spectroscopy technology is widely used in infrared spectroscopy. A spectrum that formerly required 15 min to obtain on a continuous wave instrument can be obtained in a few seconds on an FT-IR. This greatly increases research and analytical productivity. In addition to increased productivity, the FT-IR instrument can use a concept called Fleggetts Advantage where the entire spectrum is determined in the same time it takes a continuous wave (CW) device to measure a small fraction of the spectrum. Therefore many spectra can be obtained in the same time as one CW spectrum. If these spectra are summed, the signal-to-noise ratio, S/N can be greatly increased. Finally, because of the inherent computer-based nature of the FT-IR system, databases of infrared spectra are easily searched for matching or similar compounds. 

Some lasers produce a continuous-wave (CW) beam, where the timescale of the output cycle is of the same order as the time taken to remove photons from the system. CW lasers can be modified to produce a pulsed output, whereas other lasers are inherently pulsed due to the relative rates of the pumping and emission processes. For example, if the rate of decay from the upper laser level is greater than the rate of pumping then a population inversion cannot be maintained and pulsed operation occurs. 

The large conjugation system required for NIR dyes may render the dyes unstable when continuous excitation is applied. But the best signal-to-noise ratios are obtained when the residence time approaches the average bleaching time of the dye. Therefore, the dye should be able to withstand continuous-wave laser excitations. 

The representative example of this type of laser is the CO2 laser. Laser oscillation is achieved on many rotational lines within two vibrational transitions of the molecule. Without any line selection, the system oscillates at only around 10.6 /u.m. This transition is found to give a continuous wave (cw) output power of several kilowatts with an efficiency of around 30 %, which is quite exceptional for a gas laser. 

All chemical laser systems discussed so far were operated in a pulsed mode and they need either flashlamp excitation or a gas discharge to initiate the chemical reaction by producing free radicals. Recently these limitations have been overcome and pure chemical lasers with continuous-wave operation have been developed. 

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