Line frequency

One such index is line frequency, which provides indications of instability. Modulations, or harmonics, of line frequency may indicate the motor s inability to find and hold magnetic center. Variations in line frequency also increase the amplitude of the fundamental and other harmonics of running speed. 

Many electrical problems, or problems associated with the quality of the incoming power and internal to the motor, can be isolated by monitoring the line frequency. Line frequency refers to the frequency of the alternating current being supplied to the motor. In the case of 60-cycle power, monitoring of the fundamental or first harmonic (60 Hertz), second harmonic (120 Hz), and third harmonic (180 Hz) should be performed. 

Slip frequency is the difference between synchronous speed and actual running speed of the motor. A narrowband filter should be established to monitor electrical line frequency. The window should have enough resolution to clearly identify the frequency and the modulations, or sidebands, that represent slip frequency. Normally, these modulations are spaced at the difference between synchronous and actual speed, and the number of sidebands is equal to the number of poles in the motor. 

Many electrical problems cause an increase in the amplitude of line frequency, typically 60 Hz, and its harmonics. Therefore, a narrowband should be established to monitor the 60, 120, and 180 Hz frequency components. 

The motor (usually working in vacuum) is moved by a special current power supply. The rotor turns at 104-105rpm, usually a multiple of the line frequency. The pumping speed of a turbo pump unit depends on its rotational speed. High-speed turbo pumps need more frequent maintenance interventions. In some turbo pumps, a low-speed mode allows operation up to 10 1 torr. However, full rotational speed is achieved at pressures... 

When a compound is irradiated with monochromatic radiation, most of the radiation is transmitted unchanged, but a small portion is scattered. If the scattered radiation is passed into a spectrometer, we detect a strong Rayleigh line at the unmodified frequency of radiation used to excite the sample. In addition, the scattered radiation also contains frequencies arrayed above and below the frequency of the Rayleigh line. The differences between the Rayleigh line and these weaker Raman line frequencies correspond to the vibrational frequencies present in the molecules of the sample. For example, we may obtain a Raman line at 1640 cm-1 on either side of the Rayleigh line, and the sample thus possesses a vibrational mode of this frequency. The frequencies of molecular vibrations are typically 1012—1014 Hz. A more convenient unit, which is proportional to frequency, is wavenumber (cm-1), since fundamental vibrational modes lie between 4000 and 50 cm-1. 

Treating vibrational excitations in lattice systems of adsorbed molecules in terms of bound harmonic oscillators (as presented in Chapter III and also in Appendix 1) provides only a general notion of basic spectroscopic characteristics of an adsorbate, viz. spectral line frequencies and integral intensities. This approach, however, fails to account for line shapes and manipulates spectral lines as shapeless infinitely narrow and infinitely high images described by the Dirac -functions. In simplest cases, the shape of symmetric spectral lines can be characterized by their maximum positions and full width at half maximum (FWHM). These parameters are very sensitive to various perturbations and changes in temperature and can therefore provide additional evidence on the state of an adsorbate and its binding to a surface. 

The approximation switch is supplied with 120 or 230 VAC at a line frequency of 50 until 60 cps by a 3 core line. The approximation switch otters protection against vandalism and enables a simple installation. 

Electrical Resistance and Percent Llgnt Transmittance. Low frequency electrical resistance measurements were made on a conductivity bridge (Model RC-18, Industrial Instrument, Cedar Grove, N.J.) at a line frequency of 1 KC. Beckman conductivity cell with cell constant 1.0 cm was used. The percent transmission was also monitored for each of the mixtures at 490 nm (Spectronlc 20, Bausch Lomb Co., Rochester, N.Y.). 

Figure 1 shows the Raman spectrum of Hb obtained with 406.7-and 413.1-nm excitation and the spectrum of monomeric, four-coordinate Ni protoporphyrin in aqueous micellar solution (9). Excitation at 413.1 nm is at resonance with the red component of the split Soret band of Ni-reconstituted hemoglobin at 406.7 nm the blue component of the Soret band is selectively probed. Comparison of the spectra shows that two sets of marker line frequencies exist. One set (labeled 4 in Figure 1) is enhanced by resonance with the blue Soret component the other set (labeled 5) is enhanced by excitation of the red Soret component. Thus, the shifts in the core-size lines in going from set 4 - 5 are -39 cm (i/-q at 1657 cm ), -20 cm cm ), and -34 cm 1 19 cm ). 

Quantum-theoretical calculations also predict a shift in line frequency under the latter condition. References and additional detail on all of the material in this section are given by Penner (1959). 

In reality the individual lines obtained after the Fourier transformation are composed of both absorptive A(f) and dispersive D(f) components. This non-ideality arises because of a phase shift between the phase of the radiofrequency pulses and the phase of the receiver, PHCO, and because signal detection is not started immediately after the excitation pulse but after a short delay period A. Whereas the effect of the former is the same for all lines in a spectrum and can be corrected by a zero-order phase correction PHCO, the latter depends linearly on the line frequency and can be compensated for by a first-order phase correction PHCl. Both corrections use the separately stored real and imaginary parts of the spectrum to recalculate a pure absorptive spectrum. 

The selection rule (8.31) allows only one nucleus to change its Mf value in a transition, and that change is 1. Hence for an NMR transition of one of the A nuclei, the line frequencies (at fixed B0) are... 

The simplified analysis is valid only when conditions (1) and (2) are met. Otherwise, the line intensities deviate considerably from the binomial pattern, the line frequencies differ considerably from those of the first-order analysis, and the first-order analysis may even predict the wrong number of NMR lines. (Even for ethanol, which was discussed above as an A3M2X system, a good NMR spectrometer will show that there are small but significant deviations from a first-order spectrum.)... 

NMR can thus be used to study rate processes whose frequencies are of the same order of magnitude as the separation between the corresponding NMR line frequencies this corresponds to species with lifetimes in the range 1 to 10-3 sec. An illustration is the F19 NMR spectrum of SF4. At - 100°C, the spectrum consists of two triplets, as expected for a molecule with two different kinds of F atoms (Section 8.6). At room temperature, however, only a single peak is obtained, indicating that rapid exchange of the fluorine atoms is occurring. 

Each value of F corresponds to a different relative orientation of J and I and gives a slightly different energy. Thus each rotational level is split into 2/ + 1 (or 2J + 1 if 1 >J) components, and the microwave line frequencies... 

Consider the line frequencies of an electronic transition. The quantity T e Tf is some constant for the pair of electronic states involved, and simply determines which region of the electromagnetic spectrum the transition falls. The positions of the vibrational bands are determined by... 

THE ADAPTATION OF THE SEPARATOR TO VARIOUS DRIVES AND THE LINE FREQUENCY appear from the type denomination - see below. 

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