Transient waveforms

Figure 7. The rate of loss of Mn(C0)5 is plotted as a second order decay. The data were obtained at 2004.3 cm"1. The inset is a transient waveform at this frequency which covers a 2 ms time range.

Beware of artefacts This cautionary remark should always be kept in mind when carrying out flash photolysis. Stray light and fluorescence, acoustic shock waves and inhomogeneous transient distributions produced in the sample by focused laser pulses, extraneous electronic pulses from flash lamps or Q-switches, signal echoes and the like often distort the transient waveforms or spectra. 

Finally, transient potential/current waveforms may be used for polymerization. Cyclic voltammetric growth has mostly been used to carry out mechanistic studies. The use of pulsed current or potential is not a common practice. Recently, however, pulsed-current methods28 29 have been used by Mitchell and coworkers to produce more ordered anisotropic films. The use of transient waveforms adds another dimension to electropolymer growth, because the oxidation/reduction of the polymer according to Equation 2.2 will occur during growth, and the effect of this on the polymerization process must be considered. 

Transient waveforms can also be used to modify the monomer prior to polymerization in situ. For example, the polymerization of monomer 1 does not proceed if a constant positive potential is applied. 

However, when a transient waveform is used, reduction of monomer 1 to form 2 can occur at negative potentials. The polymerization of 2 proceeds according to Equation 2.3 as the working electrode is exposed to more positive potentials.30... 

Earth-return impedance has been well discussed, and its effect on the wave-propagation characteristic and the transient waveform is well-known, as is clear from a number of publications. Earth-return admittance [8,9,39,40], however, is neglected in most studies on wave propagation and surge characteristics, and its significant effect is not well understood [8,9,40, 41, 42 3]. 

Seismic signals are usually transient waveforms radiated from a localized natural or man-made... 

By the immediate first current zero it is assumed that the contacts have travelled sufficiently apart to achieve the required deionization and have built up adequate dielectric strength to withstand at least 0.95 V, . If the circuit does not interrupt at the immediate current zero at a which is so near to the point of chopping Vt , the interruption will take place only by the next current zero at point h and result in another 260 strikes by then. To study more accurate behaviour of an intenupter, with the number of restrikes and the formation of the actual transient voltage waveforms on current chopping, oscillograms similar to those during a short-circuit test may be obtained (Section 14.3.6). 

A too MHz or higher bandwidth, time-based oscilloscope. The bandwidth is especially needed for switching power supply design. A digital oscilloscope may miss important transients on some of the key waveforms, so evaluate any digital oscilloscope carefully. 

Most of the types described above have the facility for single-shot operation if it is necessary to measure single events (i.e. transients). In these cases, the timebase is triggered by the start of the transient. The limitation is the persistence of the screen luminescence since the event only occurs once, rather than a repetitive series of events, as happens with a periodic waveform where the trace is, in effect, overwritten during each operation of the timebase. 

The waveform in Figure 43.18 illustrates theoretically the unique frequencies and transients that may be present in a machine s signature. Figure 43.18(a) illustrates the complexity of such a waveform by overlaying... 

For routine monitoring of machine vibration, however, this approach is not cost effective. The time required to manually isolate each of the frequency components and transient events contained in the waveform is prohibitive. However, time-domain data has a definite use in a total plant predictive maintenance or reliability improvement program. 

What is not clock instability If, for example, you have a Buck with 100% duty cycle, you may find that under transient conditions, the switch will stay completely ON for several cycles. But that is normal. Similarly, on an IC with low-side current sensing, pulses may be omitted entirely under sudden transients. That too is normal. So don t forget to interpret the scope waveforms you see, with due regard to the part s architecture and the applied conditions, not just the topology. 

One of the more useful functions of the DC Sweep is to plot transfer curves. A transfer curve usually plots an input versus an output. A DC transfer curve plots an input versus an output, assuming all capacitors are open circuits and all inductors are short circuits. In a DC Sweep, all capacitors are replaced by open circuits and all inductors are replaced by short circuits. Thus the DC Sweep is ideal for DC transfer curves. The Transient Analysis can also be used for DC transfer curves, but you must run the analysis with low-frequency waveforms to eliminate the effects of capacitance and inductance. Usually a DC Sweep works better for a transfer curve. The one place where a transient analysis works better is plotting a hysteresis curve for a Schmitt Trigger. For a Schmitt Trigger, the input must go from positive to negative, and then from negative to positive to trace out the entire hysteresis loop. This is not possible with a DC Sweep. 

It is important to realize the difference between the AC Sweep and the Transient Analysis discussed in Part 6. The AC Sweep is used to find the magnitude and phase of voltages and currents. The Transient Analysis is used to look at waveforms versus time. An example of a waveform versus time is ... 

We will now set up the AC Sweep for this circuit. Remember that the AC Sweep gives us the phase and magnitude of sinusoidal waveforms at specified frequencies. For example, if Vy = 5sin(1000t + 30), the result of the AC Sweep will be 5 for the magnitude and 30 for the phase. If you want to see Vy displayed as a function of time, you must run a Transient Analysis. 

This graph shows us a voltage versus time. Use the Transient Analysis to obtain a waveform versus time. In the time domain the equation for this waveform is vx(t) = 5sin(2/r lOOOf + 0°). This waveform has an amplitude of 5 V and a frequency... 

The Transient Analysis uses the sinusoidal voltage waveform when it performs the simulation. This circuit would not work if an AC Sweep were used. To set up a Transient Analysis, select PSpice and then New Simulation Profile from the Capture menus ... 

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