eDAQ Picostat, User Manual

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Chapter 5 — Techniques 63
Linear Scan Techniques
Linear sweep or cyclic voltammetry are usually best performed with
EChem software. However, Scope also incorporates Stimulator… and
Output Voltage… commands which can be used to control the analog
output of the
e-corder to create a waveform suitable for these
techniques (albeit less conveniently than with the EChem software).
With Scope software up to 2560 points can be collected on one
channel at a rate of up to up to 100 kHz on both channels.
Fast Cyclic Voltammetry
Scope software has a number of features that can perform Fast Cyclic
Voltammetry (FCV). These are accessed via the Stimulator… and Output
Voltage… commands in the Setup menu,
Figure 5–1 .
The base potential is set by using the Stimulator Constant Output dialog
box while the waveform is generated using the Stimulator Up & Down,
Figure 5–2 , or Triangle, Figure 5–3 , waveforms. See the Scope
Software Manual for further details.
In Figure 5–2 the base potential has been set to –1.00 V and a
potential ramp has been set up to go from –1.00 to +1.00 V and back
again over a period of 40 ms using the Up & Down waveform option.
This corresponds to a scan rate of 50 V/s.
Figure 5–3 shows an example of a positive and negative cyclic
waveform. The base potential has been set to +0.20 V and a potential
ramp has been set up to go from +0.20 to +0.80 V back again to
–0.40 V and finally return to +0.20 V, over a period of 20 ms using
the Triangle waveform option. This corresponds to a scan rate of
120 V/s.
The Triangle waveform option always starts a scan in the centre of the
potential limits, while the Up & Down waveform option starts a scan at
one, or the other, of the potential limits.
Ideally, FCV requires a smooth analog ramp, and so it is desirable to
make the steps in the applied waveform output as small as possible.
The
e-corder output is controlled by a DAC (digital-to-analog convertor)
is the value of which is updated whenever a new data point acquired.