Impedance references

Z 2 - Secondary circuit impedance referred to the primary side Z- Load (burden) impedance... 

A few comments are in order on the probable validity of conclusions based on this equivalent circuit to real cells. Quite simply stated, real cells that are properly designed will have the same properties as dummy cells of the same values of Rs, Ru, and Cdl. Important design features of a cell are (1) equal resistance between all points on the surface of the working electrode and the auxiliary electrode (2) low-impedance reference electrode and (3) low stray capacitance between electrodes, between leads, and to shields. Spherical symmetry is a good, but somewhat inconvenient, method of meeting the first requirement a parallel arrangement also works with planar electrodes. At the very... 

Boundary impedances refer either to heterocontacts, such as the contacts of the electrode to the electrolyte or contacts between the grains of different phases in composites, or to homocontacts, i.e., grain boundaries. In this chapter, we restrict ourselves to resistive... 

In three-electrode measnrements, the main source of error at high frequencies is the reference electrode. It is advisable to use a low-impedance reference electrode or a qnasi-reference electrode such as an annealed Pt wire when making EIS measurements above 100 kHz. Lead lengths should be kept to a minimum to minimise stray indnctance and capacitance, and the cell design should be optimised to minimise series resistance losses glass frits used to separate the counter-electrode compartment are a common source of high-frequency artefacts, and these should be avoided. 

For high-impedance reference electrodes, or for potentiostats with a high input capacitance, one should consider using a so-called quasi-reference electrode. This is a piece of Pt wire that is immersed in the electrolyte next to the normal reference electrode, and connected to the reference electrode via a small capacitor, as shown in Fig. 3.15. The capacitor blocks any dc signals, so for constant or slowly varying... 

Z Cco) Zr( >) Sample impedance Reference impedance < .. > Correlation function Averaged quantities... 

The nonideal characteristics of a transformer include core and winding losses, presence of leakage fluxes, and finite permeability of the core. Hence, the actual model should include the physical representations of these nonideal characteristics. This is shown in Fig. 10.105(b), where the shunt magnetization and core loss components have been ignored for the sake of convenience. Such approximations are common in transformer analysis and only cause trivial inaccuracies in computation. Figure 10.106 shows the equivalent circuit of Fig. 10.105(b) with the secondary-side impedance referred to the primary side. 

The circuit configuration (microstrip, stripline, etc.) is the basic structure of the interconnect. The general relationship of the physical parameters to impedance is such that impedance is an inverse function of conductor width, dielectric constant, and conductor thickness, and a direct fxmction of the dielectric thickness or spacing between the signal conductor and the impedance reference planes. 

Fig. 5.17 Eliminating the effect of a high impedance reference electrode on impedance spectroscopy by compensating the low pass characteristic through an additiontd capacitor...

A resonance in the layered stracture occurs when echoes between two boundaries travel back and forth due to differences in acoustic impedances at the boundaries. For multi-layer structures a number of resonances can be observed depending on their geometry and condition. For each particular defect-free structure and given transducer we obtain a characteristic resonance pattern, an ultrasonic signature, which can be used as a reference. 

The sweeping test, following X, Y and Z axes, on the aluminum plate containing four standard defects and the processing software comparing between the impedance variation of the sane reference and the sample to be controlled allow the reconstitution of an image of the piece. 

There are two procedures for doing this. The first makes use of a metal probe coated with an emitter such as polonium or Am (around 1 mCi) and placed above the surface. The resulting air ionization makes the gap between the probe and the liquid sufficiently conducting that the potential difference can be measured by means of a high-impedance dc voltmeter that serves as a null indicator in a standard potentiometer circuit. A submerged reference electrode may be a silver-silver chloride electrode. One generally compares the potential of the film-covered surface with that of the film-free one [83, 84]. 

Cells need not necessarily contain a reference electrode to obtain meaningfiil results as an example, if the two electrodes in figure A2.4.12 are made from the same metal, M, but these are now in contact with two solutions of the same metal ions, M but with differing ionic activities, which are separated from each other by a glass frit that pennits contact, but impedes diffusion, then the EMF of such a cell, temied a concentration cell, is given by... 

The potential of the working electrode, which changes as the composition of the electrochemical cell changes, is monitored by including a reference electrode and a high-impedance potentiometer. 

In maldug electrochemical impedance measurements, one vec tor is examined, using the others as the frame of reference. The voltage vector is divided by the current vec tor, as in Ohm s law. Electrochemical impedance measures the impedance of an electrochemical system and then mathematically models the response using simple circuit elements such as resistors, capacitors, and inductors. In some cases, the circuit elements are used to yield information about the kinetics of the corrosion process. 

Z = impedance of the motor windings referred to the stator side per phase... 

Note The impedances marked on Figure 13.1.6 refer to positive phase. sequence impedances only. Faults that are non-symmelrical alone... 

To establish the minimum fault level, impedances of the feeding lines from the source of supply up to a selected point, at which the fault level is to be determined, must be added. For a step-by-step calculation to arrive at such a fault level refer to lEC 60909 and the literature on the subject as well as the references at the end of this chapter. 

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