Pulsed-current charging

The differential-pulse operation results in a very effective correction of the charging background current. The charging-current contribution to the differential current is negligible, as described by... 

To overcome these problems, most voltammetric detectors have used pulsed waveforms such as staircase , squarewaveand differential pulseThe current is sampled at the end of the pulse after the charging current has decayed. In addition, because the charging current is typically the major current source, iR problems are not as severe. Last has described a coulostatic detector based on charge pulses instead of potential pulses which eliminates iR and charging current... 

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] ... 

Under such conditions no faradaic reaction takes place during the charging pulse. Once on open circuit, the capacitor will be discharged through the faradaic resistor, R. It is easy to derive the form of the decay transient. On the one hand, the current is given by ... 

Figure 3.47 Potential-charge density transients from galvanostatic pulse experiments in the system Au(111)/10-3 M Bi(C104)3 + 1 M HCIO4 at T= 298 K [3.117], Initial underpotentials A i/mV= 110 (1) 190 (2) 220 (3) 223 (4) 225 (5), anodic pulse current densitiy i = 20 mA cm. ...

Figure 1. Potentiostatic (pulse) current-time curves at hanging Hg-drop electrode. Solid line = 10 M Cd in 1 M KNOj dotted line = charging current from 1 M KNOj electrolyte.

Fig. 9.10. Examples of pulsed-current charge techniques. Dotted lines are for rests (zero current), low-current discharges or discharge-rest combinations.

The pulse is usually referred to as the signal (for the preamplifier). While the signal from semiconductor detectors is used as a charge pulse, most other detectors immediately convert the current to a voltage drop over a resistor. In either case, the output from the preamplifier is usually a voltage pulse. Preamplifiers are often integrated with the detector. 

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