Real-time computer prediction of end points in controlled-potential coulometry

Stephens, F.B.; Jakob, F.; Rigdon, L.P.; Harrar, J.E.

doi:10.1021/ac60289a007

Cited by 21 publications

(13 citation statements)

References 18 publications

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“…Figure 12 shows current-time curves for the reduction of U(V1) in 0.5M H&04 by means of digital control. Under accurate potential control, the log idc vs. t plot is concave upward, as it is here, because of the intermediate disproportionation of U(V); whereas, if the potential becomes less negative, the plot is linearized (18). Figure 13 illustrates the response of the system under considerably higher-resistance electrolyte and cell conditions.…”

Section: Results and Discussion Preliminary Studiesmentioning

confidence: 96%

“…The system closed-loop response, Equation 18, by solving the quadratic for the denominator, can be written where (MO)…”

Section: Appendix 111mentioning

confidence: 99%

“…Other potentialities include a greater flexibility of command voltage waveform, multivariable control, user-interactive operation, digital filtering, simultaneously performing other electrochemical data processing, and incorporation of iR compensation techniques such as those of Bezman (16) or Britz and Brocke (17). In controlled-potential coulometry, the operations of current integration, automatic background correction, and final integral prediction (18) might be included in the computer program. A further incentive for investigating the use of DDC in electrochemistry is that the recent rapid development of microprocessors (19,20) holds the promise of performing this function with very compact, still less expensive hardware.…”

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confidence: 99%

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Application of direct digital control of electrode potential to controlled-potential electrolysis experiments

Pomernacki¹,

Harrar²

1975

Anal. Chem.

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A mlnlcomputer program and electronlc hardware have been developed for controlllng the potentlal of an electrode through the medlum of an algorlthm wlthln the computer. The control algorlthm found to be satlsfactory Is the dlscrete equlvalent of proportlonal-plus-Integral actlon. Control func= tlone are carrled out In assembly language at a sampllng rate of 1 kHz; the parameters that govern the control actlon and electrolysls condltlons can easlly be changed on-llne vla a hlgh-level conversatlonal language. Theory has been developed for guidance In tunlng the controller for varlous electrolysls cell characterlstlcs. Detalled control obJectlves and speclflcatlons have been formulated for typical electrolysls experlments. The system has been tested wlth mercury-pool and platlnum worklng-electrode cells, demonstratlng that the control objectives can be met and that the theory Is useful. System rlsetlmes of lese than 8 msec can be achleved, and steady-state control errors are not slgnlflcant. A malor fractlon of the tlme durlng each sampllng perlod ls available for other data processlng.The direct digital control (DDC) of the potential of the working electrode in a 3-electrode cell has been viewed as an interesting possibility (1, 2 ) ever since the advent of minicomputers. In contrast to computer-controlled potentiostats (see, for example, Refs. 1-61, where the feedback control is still accomplished by means of an analog potentiostat, DDC of the electrode potential is a concept in which the control action is generated by means of a computational algorithm within the computer. This approach is also different from the type of digital control described by Goldsworthy and Clem (7, 8) and White (9), in which the control is effected through measurement of the electrode potential by means of a differential comparator, followed by a digital output. In their technique, which does not involve the use of a computer, the control action and its characteristics are fixed in hardware.Direct digital control via software has been widely implemented in industrial process control (10-121, but for a number of reasons has not yet found application in electrochemistry. One reason has been that a speed of response comparable to that of analog circuitry could not be attained because of computational speed limitations in the computer. Now, however, the existence of faster minicomputers, digital multiply/divide circuits, and advanced software techniques have enabled significantly faster data processing. At the present time, DDC would appear to be practical at least for laboratory-scale controlled-potential electrolysis, and possibly analytical voltammetry, because these techniques do not require very high control speeds.A second factor hindering the development of DDC in the laboratory has been the much greater cost of the digiAuthor to whom correspondence should be addressed.tal, compared to the analog approach. However, when the ubiquity and versatility of the minicomputer is considered, the use of DDC can be regarded much more favorably. ...

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Section: Results and Discussion Preliminary Studiesmentioning

confidence: 96%

“…The system closed-loop response, Equation 18, by solving the quadratic for the denominator, can be written where (MO)…”

Section: Appendix 111mentioning

confidence: 99%

mentioning

confidence: 99%

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Application of direct digital control of electrode potential to controlled-potential electrolysis experiments

Pomernacki¹,

Harrar²

1975

Anal. Chem.

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“…Because the oxidation of nitrite is totally irreversible, the background current at +0.95 V is low, and nitrite is stable in the recommended supporting electrolyte, the precision and accuracy of the analysis are not greatly dependent on the time of the electrolysis or the surface condition of the electrode. However, if desired, the time of electrolysis can be significantly shortened by predictive coulometry (9), since, for a given electrode condition and applied potential, the electrolytic rate parameter is relatively constant.…”

Section: Resultsmentioning

confidence: 99%

“…Correct the results for the background consisting of the accumulated charge at the time of prediction and the quantity 2h¡k ( 9), where i>, is the constant background current and k is the electrolytic rate constant. The k value can be estimated with sufficient accuracy from the time of a complete electrolysis (k = 6.9/to.<m), or it can be determined directly (9). The sum of the accumulated background charge (id) and 2 i>Jk should not exceed the equivalent of 0.003 mg of nitrite.…”

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confidence: 99%