Impedance determination

Put 2 cc of the test fluid on the film and immediately place the bar on the film, (Do not drop the bar onto the film.) The clamp must be such that the bar is guided vertically, but not impeded. Determine the time required for the bar to penetrate the film. Duplicate trials should be made. Blow test jar free of solvent between trials. 

In the faradaic impedance measurements described above (Section 10.1.1), the impedance determined by the bridge is a whole-cell impedance and includes contributions from the counter electrode s interface. Processes at the counter electrode are not usually of interest hence the impedance at that interface is intentionally reduced to insignificance by employing a counter electrode of large area. 

The sub-transient impedance determines the initial decay, i.e. in the first cycle or so. Therefore the emfs E" and E, together with the reactances Xj and X j, need to be used for calculating the fault currents. In a similar way to induction motors, the synchronous motors will contribute to fault-making dnty reqnirements. However, they will also contribute towards the fault-breaking duty because of the transient effects. 

The reactance, X, describes that part of the DUT that behaves as a capacitor or inductor, while the resistance term, R, describes that part of the DUT that behaves as a resistor reactance indicates charge storage aspects of the DUT and resistance indicates dissipative aspects. The magnitude of the impedance, determined by the square root of the sum of the squares of the resistance and reactance [1], and the phase angle are determined by... 

Figure 4.4.12. Steady state polarization curves for iron in NaS04-H2S04 solutions according to Keddam et al. [1981] (a) Simulated curves, b) Experimental data. Rotating disk electrode (rotating speed = 1600rpm, diameter = 3 mm), T = 25 0.2°C. (From M. Keddam, O. R. Mattos, and H. J. Takenouti, Reaction Model for Iron Dissolution Studied by Electrode Impedance Determination of the Reaction Model, J. Electrochem. Soc., 128, 257-274, [1981]. Reprinted by permission of the publisher. The Electrochemical Society, Inc.)...

M. Keddam, O. R. Mattos, and H. J. Takenouti [1981] Reaction Model for Iron Dissolution Studied by Electrode Impedance. Determination of the Reaction Model, J. Electrochem. Soc. 128, 257-266 128, 266-274. 

When the acoustic waves move into the boundary of the propagation media, acoustic impedance determines basic characteristics such as reflection or transmission. Referring to Figure 33.1, if Zp is the acoustic impedance of the piezoelectric element, is the acoustic impedance of air, Z is the acoustic impedance of the acoustic matching layer, and d is the thickness of the acoustic matching layer, acoustic impedance matching conditions can be represented by (33.2), with thickness being represented by (33.3) [3]. 

Figure 16.4 Orthogonal signal correlation principle of a frequency response analyzer for impedance determination.

Here, Z and Z" (also often represented as Re(Z) and -Im(Z), respectively) represent the real and imaginary part of the impedance determined as follows ... 

Generally it is preferable to carry out an impedance determination in parallel form and later convert the experimental data if series quantities are required. The parallel form of measurement minimizes stray field and stray impedance effects. It also permits a common reference terminal for the resistive and reactive components of the sample measuring circuit. 

Ferris, C. D., 1963, Four-electrode electronic bridge for electrolyte impedance determinations, Rev. Sci. Instr. 34(1) 109-111. 

It should be emphasized that the loci shown all pertain to cells that had been stored for about 24 h between the end of discharge and the impedance determination. This was necessary owing to changes which occurred in the frequency response in the period immediately following a discharge. These changes were very subjective and de-... 

Reference has already been made in Chapter 5 to the exploitation of a resonance oscillation of a moving apparatus element in the measurement of dynamic viscoelastic properties, commonly used in characteristic impedance determinations. This principle is frequently employed for measurements on soft solids and will now be described in more detail. 

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