Duty factor

Many crane manufacturers specify that the motor should be suitable for half an hour or one hour duration according to the British practice still followed in some countries. In fact, it is not possible to correlate precisely these ratings with any of the duty factors. Hence the motors are designed for any of the duty factors of 15%, 25%, 40% and 60%. In fact the duty factors for different types of cranes have been standardized, depending upon their operation, after several years of experience. For example, the cranes operated in steel industries have different types of duty factors as follows ... 

For steel mill auxiliary drives or for material handling equipment, the duty factor normally chosen for slip-ring motors is either 40%c or 60%. 

Duty cycles Continuous duty (CMR) (S ) Periodic duties Factor of inertia (FI) Pleating and cooling characteristic curves Drawing the thermal curves Rating of short motors Equivalent output of short time duties Shock loading and use of a flywheel... 

The size requirements of a semicontinuous unit k for product i are characterized by duty factors Dik whose physical meaning is similar to the size factors, and the processing rates Rk the duty factor is related to the processing time for semicontinuous equipment as follows ... 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

Discussion of the benefits that TOF-MS may yield when applied to inorganic analysis is incomplete without also considering some of the current disadvantages of the approach. Perhaps the most noteworthy is the low duty factor of the TOF-MS. 

If we again consider the example of ICP-MS, the ion beam travels at an approximate velocity of 2.3 X 103 m/sec and fills the 1-inch extraction zone in approximately 11 (isec. If the mass spectral repetition rate is 20 kHz, then 50 psec is required to generate a mass spectrum, translating to a duty factor of 22%. Under similar conditions, we might expect a duty factor of 0.007% from a swept-beam approach. 

The efficient transport of ions through any mass spectrometer is vital, but it is perhaps of special concern within TOF-MS because of the duty factor issues and the excellent transmission efficiencies of which these spectrometers are capable. 

In the first instrument, sensitivity and limits of detection were constrained by the total ion beam current measured after the extraction region of the TOF-MS [42]. Although pulser circuitry limited the repetition rate to 7.1 kHz and a duty factor of 3.5%, detection limits ranged from 0.03 to 3 ppb using ultrasonic nebuliza-tion [16]. Mahoney et al. later reported on improvements to the same orthogonal ICP-TOF-MS [29]. The use of a commercial skimmer cone and quadrupole doublet in the extraction optics led to an increase in primary ion current from 2 nA to 50 nA [29]. This, along with electronic improvements allowing a 16-kHz spectral-repetition rate, dropped limits of detection to 1-10 ppt when ultrasonic nebuliza-tion was utilized. 

Another significant challenge remains in further increasing the efficiency with which sample species are utilized through increased ion throughput and duty factor. Currently many of the ions generated by continuous ionization sources are lost because of the pulsed nature of the instrument. Realization of higher duty factor and the unit transmission efficiency of which TOF-MS is capable could propel the TOF-MS into a sensitivity realm well beyond that of current mass analyzers. 

Various matrix addressing schemes are possible with two- and three-terminal devices. For more information, the reader is referred to an early paper of the RCA group (Lechner et al., 1971). Matrix addressing differs from multiplexing in that the LC can be driven at 100% duty factor, maintaining superior optical performance. 

A complete parametric study of the unsteady state mass transfer model clearly shows that tp, the pulse period, 4, the polarization, A, the aspect ratio, and DF, the duty factor have a profound effect on the evolution and the final shape of the deposit. Large polarization s and aspect ratios lead to deposition that is mass transfer controlled. This results in keyhole formation, as the concentration gradient inside a high aspect ratio trench is very large. On the other hand, when the deposition is kinetically controlled (i.e. for small values of polarization and aspect ratio) the gradient down the length of the trench is much smaller and deposition proceeds at nearly the bulk concentration. This leads to conformal deposition, as there is negligible variation in the deposition rate at the mouth and at the bottom of the trench. 

Small duty factors lead to a small drop in concentration during the ON period. Hence the deposition can be made to occur at nearly the bulk concentration. Large pulse periods... 

Figure 6 Effect of pulse period and duty factor on step coverage and deposition rate. Simulation parameters are A=4.0, w0=0.18pm, =0.003. Better step coverage can be obtained at the same deposition rate (at a given duty factor) by using smaller pulse periods. An asymptote is reached, as the pulse period is decrease. For this value of the pulse period the step coverage is maximum.

Pulse-on and off ratio is considered in the form of duty factor or duty ratio. It can be expressed as follows ... 

M. Malapati, A. Sarkar, B. Bhattacharyya, Frequency Pulse Period and Duty Factor Effects on Electrochemical Micromachining (EMM), Advanced Materials Research 264-265 (2011) 1334-1339. 

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