Capacitance Examples

Even a straight wire has some slight inductance (briefly mentioned on page 103), and any pair of wires has some slight "distributed capacitance," (examples on pages 184 and 205). For a simple "transmission line" pair of wires, if L and C... 

As an example, we look at tire etching of silicon in a CF plasma in more detail. Flat Si wafers are typically etched using quasi-one-dimensional homogeneous capacitively or inductively coupled RF-plasmas. The important process in tire bulk plasma is tire fonnation of fluorine atoms in collisions of CF molecules witli tire plasma electrons... 

Figure C3.1.1. The basic elements of a time-resolved spectral measurement. A pump source perturbs tlie sample and initiates changes to be studied. Lasers, capacitive-discharge Joule heaters and rapid reagent mixers are some examples of pump sources. The probe and detector monitor spectroscopic changes associated with absorjDtion, fluorescence, Raman scattering or any otlier spectral approach tliat can distinguish the initial, intennediate and final...

The use of a reactor in series with the ctipacitors w ill reduce the harmonic effects in a power network, as well as their effect on other circuits in the vicinity, such as a telecommunication network (see also Section 23.1 1 and Example 23.4). The choice of reactance should be such that it W ill provide the required detuning by resonating below the required harmonic, to provide a least impedance path for that harmonic and filter it out from the circuit. The basic idea of a filter circuit is to make it respond to the current of one frequency and reject all other frequency components. At power frequency, the circuit should act as a capacitive load and improve the p.f. of the system. For the fifth harmonic, for instance, it should resonate below X 50 Hz for a 50 Hz system, say at around 200-220 Hz, to avoid excessive charging voltages w hich may lead to... 

When a capacitor circuit is compensated through a series reaetor. either to suppress the system harmonics or to limit the switching inrush currents (Section 23.11) or both, it will require suitable adjustment in its voltage and capacitive ratings, fhe series reactor will dampen the switching currents but consume an inductively reactive power and offset an equivalent amount of capacitive kVAr. and require compensation. The following example w ill elucidate this. 

To determine the basic parameters of a 6% series reactor and its capacitive compensation, consider Example 23.6 with 3000 kVAr banks (1000 kVAr per phase) rated for 33.4 kV ... 

Consider the scheme of Example 23.4 having an automatic parallel switching. If we assume the closing sequence cycle to be 30 seconds, the recommended value of discharge resistance for each 20 kVAr capacitor bank having a capacitance of 120 fiF can be determined as follows ... 

To apply these data and equations to the problem of ground resistance, the maximum anticipated current must first be estimated. For practical industrial situations, Iq varies in the range 0.01-100/rA. The upper value represents extreme cases such as microfiltration and the lower value to slow flow in pipe. Typical charging currents for tank tmck loading are of the order 1 /rA (5-3.1.1). As an example, consider a system such as a tank with a capacitance less than 1000 pF. First, consider the minimum ignition voltages in Table A-4-1.3b. From Eq. (2), f L = In the case of hydrogen the mini-... 

This technique can be used to measure displacement where, in effect, the two electrodes are connected to the two bodies. It has also other applications (for example, in moisture meters where the presence of water vapor between the electrodes causes the capacitance change). 

Electrochemical analytical techniques are a class of titration methods which in turn can be subdivided into potentiometric titrations using ion-selective electrodes and polarographic methods. Polarographic methods are based on the suppression of the overpotential associated with oxygen or other species in the polarographic cell caused by surfactants or on the effect of surfactants on the capacitance of the electrode. One example of this latter case is the method based on the interference of anionic surfactants with cationic surfactants, or vice versa, on the capacitance of a mercury drop electrode. This interference can be used in the one-phase titration of sulfates without indicator to determine the endpoint... 

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

For example, the amplifier shown in Fig. 20 has a gate dimension of 5 by 20 pm with a capacitance of 100 fF this amplifer has a responsivity of 1.6 pVle. New designs by MIT Lincoln Laboratory have a gate size of 1 by 10 am, reducing the capacitance by more than a factor of ten, for a responsivity of 10-20 /xV/e-. 

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