Switching standards

Figure Bl.14.9. Imaging pulse sequence including flow and/or diflfiision encoding. Gradient pulses before and after the inversion pulse are supplemented in any of the spatial dimensions of the standard spin-echo imaging sequence. Motion weighting is achieved by switching a strong gradient pulse pair G, (see solid black line). The steady-state distribution of flow (coherent motion) as well as diffusion (spatially...

An alternative way of acquiring the data is to observe the signal. These experiments are referred to as reverse- or inverse-detected experiments, in particular the inverse HETCOR experiment is referred to as a heteronuclear multiple quantum coherence (HMQC) spectmm. The ampHtude of the H nuclei is modulated by the coupled frequencies of the C nuclei in the evolution time. The principal difficulty with this experiment is that the C nuclei must be decoupled from the H spectmm. Techniques used to do this are called GARP and WALTZ sequences. The information is the same as that of the standard HETCOR except that the F and F axes have been switched. The obvious advantage to this experiment is the significant increase in sensitivity that occurs by observing H rather than C. 

The type of duly defines the capacity of a switch or a contactor by the value of the current and the p.f. of the associated circuit, it can make or break on fault. For value.s of currents and p.f. for different duties, refer to the relevant standards as noted above. 

Nominal Highest voltage Standard one-minute Standard switching impulse (250/2500 ps) Standard lightning... 

Standard for control cables Power switching equipment Panel boards... 

X time taken by the impulse to rise from 0% to 95% of its peak value For the sake of laboratory testing and analytical studies, these surges have been represented by standard impulse waveforms. According to lEC 60060-1 a 1.2/50 /is impulse is called a standard lightning impulse, and a 250/2500 /is impulse a standard switching impulse. 

In case of static drives also generating simihir switching surges, their manufacturers provide the safe cable lengths as a standard practice. Section 6.14.1. 

Power capacitors behaviour, switching and improvement of power factor 23/773 Relevant Standards... 

Suitable lor systems svhere fre( uenl switching is not likely and the system is I ree frotn harmonic generating sources. They are the sell-healing type and their output may become reduced with lime (bectiuse of railures of capacitor elements as a result of ssvitching inrush currents and. system harmonics). If the system conditions are not conducive, an inductor coil may be provided to limit the harmonic effects (Section 23.9). Some manufacturers, as standard practice, provide an inductor coil inside the shell to contain the inrush current and also dampen the harmonics. 

The factors discussed in Section 23.5.2 give rise directly to the current drawn by the capacitor unit and indirectly add to its rating. The relevant Standards on this device recommend a continuous overload capacity of 30% to account for all such factors. A capacitor can have a tolerance of up to -t-15% in its capacitance value (Section 26.3.1(1)). All current-carrying components such as breakers, contactors, switches, fuses, cables and busbar systems associated with a capacitor unit or its banks, must therefore be rated for at least 1.3 x 1.15/,., i.e. 1.54. For circuits where higher amplitudes of harmonics are envisaged, for reasons of frequent load variations or more... 

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