RC time constant

Eigure 3-5.4.1 was constructed from data in Table A-4-1.3. It shows that hydrogen s LMIE is found for small diameter spark electrodes using a circuit having a small capacitance and hence a small RC time constant. The same general trend is also found for methane and is primarily due to reduced... 

Capacitors are often combined in series or parallel, with the resulting circuit capacitance calculated as depicted in Figure 4. An important relationship is the time constant of a capacitor. The time constant is based on the product of the resistance and capacitance and is known as the RC time constant. A capacitor in a dc circuit will charge or discharge 63.2 percent in one RC time constant. The time dependence of a capacitor is shown in the equations. 

The IFTOF technique requires the current mode of operation in which the various Resistance-capacity product (RC) time constants in the bridge are much smaller than the transit time tj. If the resistance Ri is larger than Rj, then the signal across the amplifier will be simply Rj i(t), where i(t) is the transient photocurrent. 

The primary purpose of this filter is to add a delay to a pulse or data sequence. The use of the RC time constant allows this delay to be added to both the rising and the falling edge of the pulse. The ideal response... 

PSpice has a model for LM324, but the the UA741 op-amp model was used in its place. The operation amplifier does not play a critical role in this circuit because of its slow response. The limiting parameter of the delay time is the RC time constant and not the slew rate or drive capability of the operational amplifier. The PSpice model response to a step input is shown in Fig. 3.27, and the AC results are shown in Fig. 3.28. 

Like the Wein-bridge oscillator, the Schmitt trigger only needs a power supply of 5 to 15V to begin its oscillation. This entails that the maximum lead that the clock pulse can drive is in the 1 mA range. The oscillation is controlled by the RC time constant and the hysteretic native to the Schmitt trigger. 

Above and to the right of line A, the contribution of edge diffusion will be less than 3 %. This is convenient when quantitative interpretation of the data is attempted, because the calculation of the effects of edge diffusion are somewhat more complicated than planar diffusion. Below and to the left of line B, the iR error will be less than 3 mV. Finally, it is desirable to work in the region to the left of line C where distortion of the shape of the voltammogram by the RC time constant of the cell is not significant. Figure 16.6 predicts that... 

The unknown parallel RC elements that comprise the impedance z in Figure 7 cause a series of maxima in the G/w vs. u data at wr = 1, from which the majority carrier time constant t of a single level interface state, R C, or any general RC time constant may be obtainable. Superposition of curves occurs if the individual time constants are closely spaced. 

It can be shown from Figure 11 and Equation 1 that the rise time of the signal will be controlled by the RC time constant of the circuit loading the pyroelectric current generator. The simplest case is where the heat flow into the pyroelectric is one dimensional as shown in Figure 12. Then the signal across the parallel load resistor of the pyroelect-ic element is... 

The small area of the electrode also reduces the double-layer capacitance and RC-time constant, which allows experiments to be performed at high scan rates (e.g. 100000Vs-1). 

Finally, some practical questions such as the three-electrode setup, the influence of the ohmic drop, the RC time constant, and a short discussion on the nomenclature of the potential perturbations used in this techniques are addressed in Sects. 1.9 and 1.10. 

Three-Electrode Systems. Ohmic Drop, Resistance of the Cell, and RC Time Constant... 

The greatly reduced double-layer capacitance of microelectrodes, associated with their small area, results in electrochemical cells with small RC time constants. For example, for a microdisk the RC time constant is proportional to the radius of the electrode. The small RC constants allow high-speed voltammetric experiments to be performed at the microsecond timescale (scan rates higher than 106V/s) and hence to probe the kinetics of very fast electron transfer and coupling chemical reactions (114) or the dynamic of processes such as exocytosis (e.g., Fig. 4.25). Such high-speed experiments are discussed further in Section 2.1. 

The capacitance behavior is strongly dependent on the contributing surface position in the electrode [50], If the considered surface lays deep into carbon micropores, the access time for the ions to this area will be longer and more resistive than for external carbon surfaces. In other words, it means that the deep internal areas are relatively inaccessible for short-electric impulses or for high-frequency currents. These deep surfaces contribute to the capacitance with a high RC time constant. As a result, the capacitance amplitude drops with increasing signal frequency. 

When an electrode process involves several steps, sometimes a succession of semi-circles side by side is obtained, corresponding to RC parallel combinations in series and with different RC time constants, from which it is possible to deduce the corresponding parameters. 

The time resolution of electrochemical measurements is usually limited by the RC time constant, rcen, of the electrochemical cell, which arises... 

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