Pulsed current

Measurement by quasi - constant current (steady - state value of pulse current) providing a compete tuning out from the effect of not only electric but also magnetic material properties. 

Current mode control has an inherent overcurrent protection. The highspeed current comparator provides pulse-to-pulse current limiting. This form of protection is a constant power form of overload protection (see Section 3.11). This form of protection folds back the current and voltage to maintain a constant power into the load. This may not be optimum for all products, especially where the typical failures slowly increase the failure current. Another form of overload protection can also be placed in the circuit. 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

Pulsed current experiments of aqueous acetate solutions indicate that at least in aqueous solution a platinum oxide layer seems to be prerequisite for the da arboxy-lation to occur. Only at longer pulse durations (> 10 s) is ethane produced [73,74]. These are times known to be necessary for the formation of an oxide film. At a shorter pulse length (<10"" s) acetate is completely oxidized to carbon dioxide and water possibly at a bare platinum surface [75]. The potent dynamic response in the electrolysis of potassium acetate in aqueous solution also points to an oxide layer, whose... 

The possibility that adsorption reactions play an important role in the reduction of telluryl ions has been discussed in several works (Chap. 3 CdTe). By using various electrochemical techniques in stationary and non-stationary diffusion regimes, such as voltammetry, chronopotentiometry, and pulsed current electrolysis, Montiel-Santillan et al. [52] have shown that the electrochemical reduction of HTeOj in acid sulfate medium (pH 2) on solid tellurium electrodes, generated in situ at 25 °C, must be considered as a four-electron process preceded by a slow adsorption step of the telluryl ions the reduction mechanism was observed to depend on the applied potential, so that at high overpotentials the adsorption step was not significant for the overall process. 

Fig. 15. SEM micrographs of Cu-Al deposits containing 5 a/o A1 that were prepared with different plating techniques at zavg = 0.70 mA in the 60.0 m/o AlCl3-EtMeImCl melt at room temperature (a) DC plating (b) superimposed-pulse current plating, ip = 1.254 mA, ton = 1 s, is = 0.509 mA, ts = 3 s, and (c) reverse-pulse current plating, ip = 1.254 mA, ton = 1 s, ir = 0.43 mA, tr = 0.5 s. The thickness of each deposit is approximately 5 pm based on a compact layer of pure copper. Reproduced from Zhu et al. [103]...

Figure 8 Pulsed current technique for the measurement of critical current. From Jones, T., McGinnis, W., Boss, R., Jacobs, E., Schindler, J., Rees, C., Tech. Doc. 1306 July 1988 Naval Ocean Systems Center, San Diego, CA.

Measurements on ceramic samples of both YBajCugOy and Bi-Sr-Ca-Cu-O have been made using a pulsed current technique by McGinnis et al. (18) and the temperature variation compared with the BCS value as obtained by Ambegaokar and Baratoff (52) Jc (TC-T)3/2. The data have yielded different interpretations that may be dependent on sample preparation. 

This circuit gives the user the option to use a DC current or to use a pulsed current as a load (useful for checking load-switching transients of power supplies). The 15 V input signal is dropped to 10 V by a 5 V zener in series. Switch A selects between the simple potentiometer voltage divider circuit (limited to 5 V maximum by the divider resistors)... 

CURRENT STEP, CHRONOPOTENTIOMETRIC AND PULSED-CURRENT TECHNIQUES... 

Pulsed-current techniques can furnish electrochemical kinetic information and have been used at the RDE. With a pulse duration of 10-4 s and a cycle time of 10-3 s, good agreement was found with steady-state results [144] for the kinetic determination of the ferri-ferrocyanide system [260, 261], Reduction of the pulse duration and cycle time would allow the measurement of larger rate constants. Kinetic parameter extraction has also been discussed for first-order irreversible reactions with two-step cathodic current pulses [262], A generalised theory describing the effect of pulsed current electrolysis on current—potential relations has appeared [263],... 

In order to rule out distortions of the E-J curve by extensive heating that could be induced by the very high extensive heating that could be induced by the very high dissipation levels employed here, a pulsed current power supply was used with a time duration 0 = 10 ms, a waveform repeat time of 2 s and an average over 64 pulses at the same fixed J, T and H. 

The sensitivity of NPP is greater than that of dcP because the ratio NipV dci — (31/712)1,2 is much greater than unity, provided that U. Moreover, the pulse current greatly exceeds the charging current as compared to dc current, since the charging current for a DME is given by [1-3] ... 

Thus, second pulse current density becomes independent of electrode radius when the reaction product is not initially present (VK = 0) ... 

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