Source impedance effect

Adding a pair of buffer ampHfiers before the summing stage results in an instrumentation-grade circuit, as shown in Fig. 10.287. The input impedance is increased substantially, and any source impedance effects are eliminated. More noise is introduced by the added op-amp, but the resistor noise usually can be decreased by reducing impedances, causing a net improvement in system noise. 

Another consequence of the presence of the series capacitance, Cp, is the reduction of the source impedance of the membrane in the high-frequency range. Because of this peculiar effect, a short-circuit measurement is harder to achieve in the high frequency range than in a steady state because a lower input impedance is required to achieve a short-circuit condition. Sometimes a commercial picoammeter is used to measure displacement photocurrents under a presumed short-circuit condition. However, such instruments often have an input impedance on the order of 100 kft in the megahertz frequency range. In view of the much reduced source impedance of a reconstituted purple membrane, these measurement conditions are actually closer to an open circuit than to a short-circuit condition. The measurement is often accompanied by a telltale observation that the measured current is the first time derivative of the measured photovoltage (26). A detailed analysis of this problem is presented elsewhere (19, 20). 

Active filter A form of power electronic converter designed to effectively cancel harmonic currents by injecting currents that are equal and opposite to, or 180" out of phase with, the target harmonics. Active filters allow the output current to be controlled and provide stable operation against AC source impedance variations without interfering with the system impedance. 

The philosophy to assume the impedance of the source of supply (generator or a transformer) as the impedance of the faulty circuit may be far from reality and may give a very high fault current. In actual operation, the fault intensity may be far less, as every device and component connected in the circuit will tend to add to the effective impedance of the faulty circuit and limit the magnitude of the fault current. Figure 13.15 also subscribes to this theory. But it is customary to design the systems for the worst fault conditions which, in all likelihood, may not arise, and decide the protective scheme and the current settings of the protective relays for the minimum possible fault current. 

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

This corrosion of the SEI by linear carbonate solvents would undoubtedly produce adverse effects on the performance of lithium ion cells. During longterm cycling, the damaged SEI has to be repaired constantly by the same electrochemical reactions that occurred in the initial formation process, which consumes the limited lithium ion source in the cell and increases the impedance at the electrode/ electrolyte interface. 

Ab initio calculations identify the sources of these effects for example, in unsam-rated ketones the double bond participates fully in the change in charge distribution accompanying protonation, while in the unsaturated lactones, the ring oxygen impedes this shift of electron density. 

Qi Y., Huang B., Chuang K.T. (2005) Dynamic modeling of solid oxide fuel cell The effect of diffusion and inherent impedance. Journal of Power Sources 150, 32-41. 

By not creating a resonance circuit at precisely the 5th harmonic frequency, we can minimize the possibility of the filter resonating with other loads or the source, thus forming a parallel resonance circuit at the 5th harmonic. The 4.7th harmonic filter would still be effective in filtering out the 5th harmonic currents. This is evident from the series-tuned frequency vs. impedance curve shown in Figure 4.22. 

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