10-19
Comments
The maximum data file length is 1000 points/step. The circuitry for CC is a direct
charge-to-voltage converter. The integrating capacitor that is used to accumulate
the charge in the 10
µ
C/V
Sensitivity
range is automatically discharged and reset
to zero when it nears the voltage saturation level. This operation allows a much
greater charge to be measured during the experiment. Discharging the capacitor
requires 0.5 msec during which time no charge is measured. We have never had a
situation where thishas caused a noticeable error in the output, since discharge
typically occursafter the initial large current transients have decayed and the
current isrelatively small (so the charge lost over 0.5 msec is less than the
resolution of the instrument and the expected precision of the experiment).
However, errors can occur if the initial current are very large, since this may
cause discharging at short times. Such errors are shown by discontinuities in the
Charge vs. Time
plot. If this occurs, the initial current must be decreased by, for
example, decreasing the concentration and/or the electrode surface area.
The automatic discharge is not allowed for the 100 nC/V and 1
µ
C/V ranges,
since the charge lost during the 0.5 msec may be significant.
Too much current may also cause the digital accumulators to overload. This
occurs after 32 discharge-charge cycles, and is shown by sharp discontinuities in
the
Charge vs. Time
plot as the charge drops to zero.
Graphics Menu
Single Graph
displays the
Charge vs. Time
plot as the default plot. The
Anson plot (
Charge vs. sqrt (Time)
)can be selected using the
Data Type
drop-down list box in the
Graph Options
dialog box.
Analysis Menu
The
Auto
option for
Results Graph
displays the plot selected in
Data Type
,
and the slope, intercept and correlation coefficient are listed in the
Main
window. Since data at early time points can be distorted due to the finite time
required for the potential step, the
Auto
option uses only the last 80% of the
data. An alternative line can be defined by the user through the Manual option
(the line is specified by the X values of 2 points on the plot). The slope is
reported in units of c/ms
1/2
.
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