Base frequency

For any arrangement of equal angular piston spacing (on the crankshaft), here are the fundamental or base frequencies. ... 

For single-acting cylinder, rpm/60 will be the base frequency, and all filters should be sized below this base... 

Other frequencies will also exist, but the harmonics of the base frequency will be predominant. The largest pulse will depend upon the combination of cylinders and crank throws and will occur at the point where two or more cylinders discharge simultaneously, because successive waves in phase are additive. 

In a double-acting cylinder, the base frequency will be double that of a single-acting cylinder with its harmonics as additional predominant frequencies. 

With compressors of even angular piston spacing, the fundamental (or base) frequencies may be computed as follows ... 

After the anticipated disturbing frequencies have been determined, it is necessary to begin the sizing of the filter system. The cutoff frequency should be set at least one cycle per second below the lowest frequency to be filtered. The base frequency is determined from compressor speed and should be determined at the lowest anticipated compressor speed for variable-speed compressors. The following equation is used to determine cut-off frequency for a low-pass filter ... 

The pulsation dampener must be capable of filtering the base frequency, or 10, 20, 30, 40 cycles/sec based on the rated speed, with a cut-off frequency at least one cycle/sec below the low speed frequency (8.67 cycles/sec). 

A beat frequency exists as the sum or difference of two frequencies. For a base of 10 cycles/sec and a resonant frequency of 3.48 cycles/sec, beat frequency = 10 — 3.48 = 6.52 cycles/sec, which is below the compressor base frequency of 10 cycles/sec and is acceptable. Beat frequencies of the harmonics of the base frequency will be filtered. 

For best results, the first band-pass frequency should not be an integer muldple of the base frequency. 

The maximum value of a vibration, or amplitude, is expressed as displacement, velocity, or acceleration. Most of the microprocessor-based, frequency-domain vibration systems will convert the acquired data to the desired form. Since industrial vibration-severity standards are typically expressed in one of these terms, it is necessary to have a clear understanding of their relationship. 

Used in conjunction with zero-to-peak (PK) terms, velocity is the best representation of the true energy generated by a machine when relative or bearing cap-data are used. (Note Most vibration monitoring programs rely on data acquired from machine housing or bearing caps.) In most cases, peak velocity values are used with vibration data between 0 and 1000 Hz. These data are acquired with microprocessor-based, frequency-domain systems. 

All components have one or more natural frequencies that can be excited by an energy source that coincides with, or is in close proximity to, that frequency. The result is a substantial increase in the amplitude of the natural frequency vibration component, which is referred to as resonance. Higher levels of input energy can cause catastrophic, near instantaneous failure of the machine or structure. The base frequency referred to in a vibration analysis that includes vibrations that are harmonics of the primary frequency. 

FIGURE 2. Constant-acid-constant-base frequency shift-enthalpy relationship. 

A technique for such measurements is the electrochemical quartz crystal microbalance (EQCM figure 14) [71]. Here, the working electrode is part of a quartz crystal oscillator that is mounted on the wall of the electrochemical cell and exposed to the electrolyte. The resonance frequency / of the quartz crystal is proportional to mass changes Am A/ Am. With base frequencies around 10 MHz, the determination of Am in the ng range is possible. 

Fig. 8. Constant acid-constant base frequency shift-enthalpy relations. Solid lines are constant acid lines. The phenol line also contains values for p-t-butylphenol, 4-, phenol, 0, p-chlorophenol, , m-trifluormethylphenyl, A. The acid butanol is H...

Barker et al. (1961) found such a correlation for Malachite Green cations. It is not necessary, however, that the acid and conjugate base frequency shifts should separately be related to the substituent a-values in this way for a good correlation to be obtained between a and the difference in their frequency shifts, i.e. the difference in their frequency maxima and hence in p (Sj)—pAT(S0). Figure 10 shows a plot of Av against a for substituted 5-phenylazotropolones, the acid and base forms of which separately showed very erratic... 

Synonymous versus non-synonymous change assumes that base frequencies reflect substitutional frequencies Unlike synonymous mutations, nonsynonymous changes alter primary sequence of a polypeptide and, as such, are under greater selective constraint and occur less frequently. Nonsynonymous mutations therefore warrant greater weight... 

An AT-cut quartz crystal having base frequency of 8 MHz (Sunny Electronics Co., Korea) is utilized to prepare the sensor. The electrode of the crystal is silver finished. Two... 

The MD calculated DOS is, to first-order, independent of temperature and only small anharmonic effects appear at non-zero temperatures. These anharmonic effects arise from the fact that most potential functions are not parabolic. As the displacements increase in magnitude the molecules explore non-parabolic regions of the potential and the overtone frequencies with perfect integers of the base frequency C0o> such as 2coo, 3c0o..., due to the Fourier expansion of the non-parabolic potential function. 

Figure 3. Distortion of the base frequency signal with cavitation, (a) No cavitation (b) the cavitation threshold (c) developed cavitation mode.

Fig. 2. Measuring set-up (A) photograph of the piezoelectric device and flow system, the inset shows the cell holding the quartz sensor (B) sample QCM sensor with 10 MHz base frequency (as used throughout the described experiments) (C) cross-section through the piezo-cell showing the two rubber O-rings holding the quartz plate, only one side of the sensor is in contact with the fluid (D) cross-section of the cell used for combined piezoelectric and amperometric measurements, the lid also hold a titanium wire electrode and the Ag/AgCI reference electrode.

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