Version 1.11.0
NOVA Chrono methods tutorial
1 – Chrono methods
The term Chrono methods includes all the measurements of electrochemical signals
during a well-defined sequence of steps.
In NOVA, time resolved measurements are possible using three different
measurement strategies:
•
•
•
Using the Record signals (> 1 ms) command: this command can be used
at any point in a procedure to record the signals defined in the signal sampler
for a specified amount of time and using a well-defined interval time. The
smallest possible value of the interval time is 1.3 ms. The Record signals (> 1
ms) command does not apply a potential or current value. It simply samples
the signals defined in the sampler using the specified parameters. This
tutorial provides more information on the use of the Chrono methods
command (see Section 2).
Using the Chrono methods command: this command can be used to
perform time resolved measurements with interval times smaller than 1.3
ms. The lowest interval time is roughly 80 µs or 20 µs, depending on the type
of instrument, and it depends on the type of signals to measure and the
number of signals to sample. The measured signals are defined in the signal
sampler. This tutorial provides more information on the use of the Chrono
methods command (see Section 1).
Using the Chrono methods high speed command: this command can be
used to perform time resolved measurements at the smallest possible interval
time. A dedicated fast sampling ADC module is required for these
measurements (ADC750 or ADC10M). The Chrono methods high speed
tutorial provided more information on the use of this command in
combination with the fast sampling ADC module. The maximum number of
signals that can be measured with this methods is two (choice from:
WE(1).Potential, WE(1).Current, or External).
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Table 1 provides an overview of some of the important features related to the use
of the three different commands for time resolved measurements.
Command
Smallest interval
time
Setpoint included
Real time display
Signals selection
Options support
Pause/Stop support
Fast options support
Time derivative
sampling
Record signals
(> 1 ms)
Chrono
methods
1.3 ms
~ 80 µs/20 µs 1
No
Yes
Sampler
Yes
Yes
Yes
Yes
No
Sampler
No
No
No
Chrono methods high
speed
1.33 µs (ADC750)
0.1 µs (ADC10M)
Yes
No
Hardware defined (2)
No
No
No
Yes
No
No
Table 1 – Comparison of the commands for time resolved commands
Scope of the tutorial
This tutorial explains how to use the Record signals (> 1 ms) and Chrono methods
command in NOVA to perform chrono measurements. Examples for the Autolab
dummy cell are provided.
2 – The Record signals (>1 ms) command
The Records signals (> 1 ms) command 2 is a generic recording command that can
be used at any point in a procedure to record the specified signals for a predefined
amount of time. Unlike the Chrono methods command, detailed in Section 1, the
Records signals (> 1 ms) command does not apply any potential or current value
before it starts recording.
The Record signals (> 1 ms) command is a timed command. This means that the
timing of the measurements will be defined by the internal clock of the Autolab
interface. The command can be located anywhere in the procedure editor. The
green timing line will be shown on the left of the command to indicate that this is
a timed command (see Figure 2).
The smallest possible interval time depends on the type of embedded controller used by the
instruments. Instruments fitted with the IF030 have a smallest interval time of about 80 µs, while
instruments fitted with the IF040 have a smallest interval time of about 20 µs.
2
There are two Records signals (> 1 ms) commands available in the Measurement – Chrono methods
command group. The Records signals (> 1 ms) command can be used for measurements in
potentiostatic mode while the Records signals (> 1 ms) galvanostatic can be used for measurements
in galvanostatic mode. In this tutorial, the term Records signals (> 1 ms) will be used for both
commands.
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Figure 1 – The details of the Record signals (> 1 ms) command
The Record signals (> 1 ms) command has the following parameters:
•
•
•
•
Duration: the duration of the measurement, in seconds.
Interval time (s): the sampling interval time, in seconds. This value must be
smaller than the duration value. The smallest possible value is 1.33 ms.
Signal sampler: defines the specific sampler used during the Record signals
(> 1 ms) measurement. By default, Time and WE(1).Current are measured,
but additional electrochemical signals can be added to the sampler. The
Index and Corrected time are automatically added to the data.
Use fast options (Yes/No): defines if the fast options are used. By default,
this parameter is set to No.
Note
Additional parameters are available for the Record signals (> 1 ms) command
depending on the settings defined in the Signal sampler and the Use fast options
parameter (see Figure 2).
Figure 2 – The complete details of the Record signals (> 1 ms) command
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The following additional parameters are available for Record signals (> 1 ms)
command:
•
•
Fast interval time (s): the fast interval time used to test the options if the
Use fast options parameter is set to Yes. If the Use fast options is set to No,
then the Fast interval time parameter is not shown (see Figure 1). The value
of the Fast interval time must be smaller or equal to the Interval time and it
must be an integral fraction of the Interval time 3. The smallest possible value
is 1.33 ms (see Section 2.2).
dSignal/dt sample threshold (Units/s): specifies the threshold value for the
derivative of the specified signal, in units of the signal per second. This
parameter is only shown when a time derivative signal is sampled and if the
Fast options parameter is set to Yes (see Section 2.3).
Depending on the specified parameters, the Record signals (> 1 ms) command can
use three different algorithms:
1. Standard parameters (Use fast options set to No): the signals defined in the
signal sampler are measured for the specified duration. Each data point is
recorded after the user-defined interval time. The measurement options are
verified after each interval time. More information is provided in Section 2.1.
2. Using the fast options (Use fast options set to Yes): the same strategy as in
the standard mode is used for measuring the data points but the options are
now verified after each user-defined fast interval time. This means that the
options can be modified or triggered at a faster rate that the sampling rate.
More information is provided in Section 2.2.
3. Using the fast options and the Time derivative threshold value (User fast
options set to Yes and time derivative signals sampled): the same strategy as
in the previous mode is used. The time derivative value of one or more signals
is determined using the fast interval time. For each time derivative signal, a
threshold can be defined by the user. When the absolute value of a time
derivative signal exceeds the specified threshold, the data points are
measured using the fast interval time instead of the interval time. This means
that the sampling rate can be modified depending on the derivative of one
or more signals. More information is used in Section 2.3.
2.1 – Using the Record signals (> 1 ms) command
The Record signals (> 1 ms) command is designed to measure the specified signals
using the user-defined duration and interval time. To illustrate this, a dummy cell
consisting of a resistor of 100 kΩ in series with a capacitor of 10 µF will be used in
this section (see Figure 3).
For example, with an interval time of 0.2 s, the fast interval time can be set to 5 ms but not to 7
ms.
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Figure 3 – Dummy cell used to illustrate the use of the Record signals (> 1 ms) command
This dummy cell has a characteristic RC time of 1 second. The measurements shown
in this section are performed using the following procedure:
1. The dummy cell is discharged at 0 V in potentiostatic mode for 10 s.
2. A sequence of 3 current steps is applied on the dummy cell:
a. Step 1: 0 µA, for 2 seconds.
b. Step 2: 30 µA, for 10 seconds.
c. Step 3: -30 µA, for 10 seconds.
3. After each current step, a Record signals (> 1 ms) galvanostatic, as shown in
Figure 5 is used.
Note
The same dummy cell will be used for the measurements described in Sections
2.2 and 2.3.
Figure 4 shows the result of a measurement using the standard settings of the
Record signals (> 1 ms) command.
Figure 4 – Measuring the response of the cell
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The RC circuit charges up to 3 V and –3 V during the second and third current step,
respectively. The expected potential values are observed after five seconds, which is
consistent with the RC time of the cell.
Note
The default Chrono amperometry (∆t > 1 ms) and Chrono potentiometry (∆t > 1
ms) procedures provided in the Autolab group of procedures use the Record
signal (> 1 ms) command in its standard mode (Use fast options set to No). More
information on these procedures is provided in the Getting Started manual.
2.2 – Using the fast options and fast interval time
The fast options provided by the Record signals (> 1 ms) command can be used to
check the options at a faster rate than the sampling rate.
When this options is not used (as described in Section 2.1), the options are checked
after each sampling interval time. When this option is used, the checking of the
options is decoupled from the sampling of the data. This is particularly useful for
long measurements on a cell that requires the options to be checked with a short
interval time.
Figure 5 shows an example of a measurement using a duration of 10 seconds, an
interval time of an interval time of 0.2 second. This leads to 50 points.
Figure 5 – Using the fast options
Figure 5 also shows that the fast options are used and that the fast interval time is
set to 20 ms.
Warning
The fast interval time must always be an integral fraction of the interval time. For
example, with an interval time of 0.2 s, the fast interval time can be set to 5 ms,
but not to 7 ms.
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Using these parameters, a data point will be recorded every 200 ms but the options
will be tested every 20 ms.
To illustrate this option, the following cutoff conditions will be used (see Figure 6).
Figure 6 – Cutoff conditions used for the WE(1).Potential signal
Note
More information on the cutoff options is available in the Cutoff tutorial,
available from the Help menu.
Two cutoff conditions are used:
•
•
If the WE(1).Potential is larger (>) than 2.5 V five consecutive times, the
command is stopped.
If the WE(1).Potential is smaller (<) than -2.5 V five consecutive times, the
command is stopped.
Figure 7 shows the same measurement as in Figure 4, using the cutoff conditions
specified in Figure 6 but without using the fast options.
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Figure 7 – Measuring the response of the cell, with the cutoff conditions
The Record signals (> 1 ms) commands are interrupted as soon as five consecutive
potential values are above 2.5 V or below -2.5 V.
Finally, Figure 8 shows the same measurement again, but with the fast options now
used. The fast interval time is set to 20 ms in this measurements.
Figure 8 – Measuring the response of the cell, with the cutoff conditions and the fast options
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The Record signals (> 1 ms) commands are again interrupted by the specified
conditions. Comparison with the data shown in Figure 7 reveals that the cutoff
condition was triggered as soon as a value higher than 2.5 V or lower than -2.5 V
was detected (five consecutive times) by the fast options. Since the fast options uses
an interval time of 20 ms, the cutoff is triggered after 100 ms as soon as the
measured potential is larger than 2.5 V or smaller than -2.5 V.
Figure 8 shows how the cutoff conditions are decoupled from the recording of data
points and how the fast options can be used to react on an event in the
measurement with a shorter interval time that the interval time used for recording
the data.
Note
When the fast options are used, the number of consecutive detections for a
cutoff condition no longer matches actual data points in the measured data.
2.3 – Using the time derivative threshold
The Record signals (> 1 ms) command offers one additional variation of its sampling
algorithm based on the time derivative value of one of more signals. To illustrate
this option, the same measurement as described in Section 2.2 will be used in
combination with the time derivative of the WE(1).Potential signal.
In this example, the interval time is set to 0.2 seconds and the fast interval time is
set to 0.02 s. The time derivative of the WE(1).Potential signal is added to the signal
sampler (see Figure 9).
Figure 9 – Adding the time derivative of the WE(1).Potential signal to the list of signals
sampled by the Record signals (> 1 ms) command
With the Use fast options parameter set to Yes and at least one time derivative
signal specified in the sampler, the dX/dt sample threshold parameter is
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automatically added to the Record signals (> 1 ms) command. In the example shown
in Figure 10, the dWE(1).Potential/dt sample threshold parameter, in V/s, is added
to the procedure editor.
Figure 10 – Using the time derivative threshold
Using these parameters, the time derivative of the WE(1).Potential signal will be
determined during the measurement using the fast interval time as the dt variation.
When the absolute value of the dWE(1).Potential/dt, in absolute value is larger or
equal to 1 V/s, the data points will be recorded using the fast interval time instead
of the interval time.
Figure 11 shows the measured data obtained using these parameters. The interval
time used in the measurement is 0.2 s for the whole measurement, except at the
beginning of the two potential transients, for which an interval time of 20 ms has
been used.
Figure 11 – The results obtained using the time derivate threshold option
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When the WE(1).Potential signal value exceeds 2 V and -2 V, the sampling rate
changes. All values measured at the beginning of both transients are measured
using the fast interval time. This is highlighted in Figure 12, which shows the data
from the first potential transient only (which is shown together with the measured
dWE(1).Potential/dt signal, plotted on the right-hand side axis).
Figure 12 – Details of the first potential transient (blue points: E vs t, red line:
dWE(1).Potential/dt)
While the dWE(1).Potential/dt value is larger or equal to 1 V/s in absolute value, the
recording of the data proceeds with 20 ms interval time instead of the normal 200
ms interval time.
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3 – The Chrono methods command
Unlike the Record signals (> 1 ms) command, which is used to record
electrochemical signals during a single step, the Chrono methods command
provides a very flexible framework that can be used to create a sequence of
potential or current steps 4.
The Chrono methods command is a timed command. This means that the timing of
the measurements will be defined by the internal clock of the Autolab interface. The
command can be located anywhere in the procedure editor. The green timing line
will be shown on the left of the command to indicate that this is a timed command
(see Figure 13).
Figure 13 – The Chrono methods command can be located anywhere in the procedure editor
The Chrono methods command is designed to apply a user-defined sequence of
steps on the electrochemical cell and record the response of the cell. Depending on
the number of data points, transferring the data from the Autolab to the computer
can take up to a few seconds.
The Chrono methods command is also designed to allow measurement to proceed
as quickly as possible, with the highest possible accuracy in interval time. The
measured data points can therefore only be shown at the end of the experiment.
The Chrono methods command has the following parameters
•
•
Number of repeats: defines the number of repetitions of the sequence of
steps defined in the Levels editor.
Signal sampler: defines the specific sampler used during the Chrono
methods measurement. By default, Time, Corrected time, Level, Index and
WE(1).Current are measured, but additional electrochemical signals can be
added to the sampler.
There are two chrono methods commands available in the Measurement – Chrono methods
command group. The Chrono methods command is used for chrono amperometry measurements
while the Chrono methods galvanostatic is used for chrono potentiometry measurements mode. In
this tutorial, the term Chrono methods will be used for both commands.
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To use the Chrono methods command, the sequence of steps must first be defined.
To create or edit a sequence of steps, the
button of the Chrono methods
command parameter must be clicked (see Figure 14).
Figure 14 – Opening the Chrono methods editor window
The Chrono methods editor window displays two frames (see Figure 15). The frame
on the left-hand side contains the sequence of items that will be applied during the
measurement. The frame on the right-hand displays the parameters of each
element. By default, no items are visible and no parameters are shown (Figure 15).
Figure 15 – The Chrono methods editor window
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3.1 – Creating a sequence of steps
The sequence of steps can be constructed by adding items to the sequence, using
the five buttons located on the bottom end of the frame on the left-hand side of
the window (see Figure 16).
Add an item to the sequence
Remove the highlighted item
from the sequence
Move the highlighted item up
in the sequence
Move the highlighted item
down in the sequence
Adds a copy of the highlighted
item at the end of the sequence
Figure 16 – The sequence can be edited using the five buttons located in the frame on the
left-hand side
Five buttons are available in the frame on the left-hand side (see Figure 16):
•
•
•
•
•
Add ( ): adds an item to the sequence.
Remove ( ): removes the highlighted item from the sequence.
Copy ( ): creates a copy of the highlighted item at the end of the sequence.
Move up ( ): moves the highlighted item up in the sequence.
Move down ( ): moves the highlighted item down in the sequence.
The following basic items can be used to construct the required sequence
(see Figure 16):
•
•
Step: this item creates a step in the sequence. A step is defined by three
parameters – the potential (or current), the duration and the interval time.
The default values for potential (or current), duration and interval time are 0,
0.001 s and 0.0001 s, respectively.
Level: this item creates a level in the sequence. A level is defined by two
parameters – the duration and the interval time. The default values are the
same as for the step.
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Note
The difference between a step and a level is that the level does not have a
potential or current parameter. This means that a level does not change the
applied potential or current, but only records the electrochemical signals during
the indicated duration and with a specific interval time.
Note
Combining steps and levels is useful for studying the electrochemical response of
a system. While a potential step generates a large current spike, the current
rapidly decreases and becomes controlled by mass transport. Using a step with a
short interval time followed by a level with a long interval time allows you to
record the electrochemical signals with an optimal interval time.
The Chrono methods editor window also provides two advanced items that can be
used to construct elaborated sequences:
•
•
Repeat (unsampled): this item creates a sub-sequence in the main sequence,
in which new items can be added. This sub-sequence can be repeated any
number of times, but does not generate any data points, as the
electrochemical response of the cell is unsampled for the whole subsequence. This can be useful for conditioning the electrode with a pulse
sequence, or for reducing the number of data points recorded during long
measurements.
Repeat: this item creates a new sub-sequence in the main sequence, in
which new items can be added. This sub-sequence can be repeated any
number of times and the electrochemical response of the cell is sampled
during the whole sub-sequence.
To create the required sequence using the Chrono methods editor window, click
the
button in the frame on the left-hand side and select the required item from
the popout menu (see Figure 17).
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Figure 17 – Adding items to the sequence
A step will be added to the sequence.
Click the step that was added to the sequence to display the parameter details in
the frame on the right (see Figure 18).
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Figure 18 – The details of the step parameters are displayed in the frame on the right
Note
The parameters of the Step are grouped in two sections: basic and advanced.
The step has the following default basic parameters:
•
•
•
•
•
•
Text: Step
Potential 5: 0 V
Duration (s): 0.001
Sample: Yes
Interval time (s): 0.0001
Estimated number of points: 10
Warning
The maximum duration for a single step or level is 4294 seconds.
Two additional parameters, Pre Autolab control and Post Autolab control, are
advanced settings that can be used to change the Autolab settings during the
sequence. These parameters are available in the advanced section and their use falls
outside of the scope of this tutorial (see Figure 19).
5
In Galvanostatic mode, the Current parameter is displayed instead of the Potential parameter.
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Figure 19 – Advanced parameters are available in the advanced section
It is possible to change any of the five parameters of the step. If the duration and/or
the interval time are changed, the number of points will be updated accordingly.
Change the duration of the step to 0.005 seconds (see Figure 20). The number of
points will be changed to 50.
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Figure 20 – Changing the duration or the interval time parameter modifies the number of
points
Using the same approach, it is possible to add additional steps to the sequence (see
Figure 21).
Figure 21 – Adding more steps to the sequence
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It is also possible to select any item in the sequence and create a copy of it at the
end of the sequence by clicking the
button in the toolbar.
Figure 22 – Using the
button to copy the highlighted item
The copied item is always added at the end of the sequence (see Figure 23).
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Figure 23 – The copied item is always added at the end of the sequence
The parameters for each step can be edited independently by clicking each
individual item in the sequence on the left-hand side. The highlighted item in the
sequence is shown in bold lettering (see Figure 24).
Figure 24 – Editing the parameters of each item in the sequence
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Set the duration of each step to 0.005 seconds and click the OK button to close the
editor and validate the defined sequence. This will update the parameters of the
Chrono methods command in the procedure editor view (see Figure 25).
Figure 25 – The updated parameters of the Chrono methods command in the procedure
editor
4 – A measurement using the Chrono methods command on the
dummy cell
A Chrono methods tutorial folder is located in the Program Files\MetrohmAutolab\Nova 1.11\Shared Databases\Tutorials folder (see Figure 26). Using the
database manager, set this folder as the Standard database.
Figure 26 – Loading the Chrono methods tutorial database
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Seven procedures are included in this tutorial procedure. All the procedures are
intended to be used with the standard Autolab dummy cell (see Figure 27).
The PGSTAT101 is not equipped with the Autolab dummy cell. An optional external
dummy cell can be obtained 6. It is also possible to activate the internal dummy cell,
using the Autolab control command 7.
Figure 27 – The seven Chrono methods tutorial procedures
4.1 – CM Tutorial – Example 1
Select the CM Tutorial – Example 1 procedure from the Standard group. Connect
the dummy cell (c) to the instrument and start the measurement. The procedure will
perform a measurement on the dummy cell using the following sequence (see Figure
28):
•
•
•
6
7
Step 1 – Potential 0 V, duration 0.005 s, interval time 0.0001 s.
Step 2 – Potential 0.3 V, duration 0.005 s, interval time 0.0001 s.
Step 3 – Potential -0.3 V, duration 0.005 s, interval time 0.0001 s.
Contact your Autolab distributor for more information.
Please refer to the Autolab control tutorial, available from the Help menu, for more information.
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Figure 28 – The sequence used in the Example 1 procedure
Only the WE(1).Current signal is measured during this experiment.
Press the start button to run the measurement. A message box will be displayed
before the measurement starts (see Figure 29).
Figure 29 – The message box shown during the Example 1 tutorial procedure
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 30 shows the expected current profile for this
measurement on the dummy cell.
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Figure 30 – The current profile plotted vs Corrected time measured during the Example 1
procedure (the data is displayed at the end of the measurement)
Note
The time scale displayed on the X-axis in Figure 30 has been set to Corrected
time. The corrected time is an adjusted time scale for which t = 0 s has been set
to first measured data point. The Corrected time signal is available for plotting in
the Analysis view.
Warning
The Chrono methods command automatically calculates a Corrected time signal
after the measurement. This signal is a normalized time scale, relative to the
absolute time stamp of the first data point recorded during the measurement.
This simplifies overlays using data sets from different experiments, since the
absolute timing could be different.
Close inspection of the measured data in the analysis view reveals that the number
of points measured during the Example 1 procedure (147) is smaller than the
estimated number of points (150). This discrepancy comes from a small delay
generated by the setting of a new potential value at the beginning of each step.
This delay is about twice the interval time.
4.2 – CM Tutorial – Example 2
Select the CM Tutorial – Example 2 procedure from the Standard group. Connect
the dummy cell (c) to the instrument and start the measurement. The procedure will
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perform the same measurement as the procedure used in the previous example.
However, instead of sampling only the WE(1).Current, both the potential and the
current are sampled in this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 31 shows the expected current and potential profiles
for this measurement on the dummy cell.
Figure 31 – The current (red curve) and potential (blue curve) profiles plotted vs Corrected
time measured during the Example 2 procedure (the data is displayed at the end of the
measurement)
Careful comparison of the data sets by means of the data grid reveals a significant
difference between the two tutorial measurements. Although both measurements
have the same duration, 0.015 seconds, the total number of points is not the same.
For Example 1, the total number of points 8 is 147, while the number of points
recorded during Example 2 is 66.
This difference stems from the settling of the input multiplexer of the ADC164.
When more than one signal is sampled, the A/D converter is continuously switching
between signals. The switch between signals introduces additional settling and
overhead times which increases the achievable interval time. When the practical
interval becomes larger than the specified interval time, the data points will be
measured as quickly as possible.
8
The total number of points can be slightly different.
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In the case of the data measured during the second tutorial procedure, the number
of data points is 66, which corresponds to an interval of roughly 230 µs.
Note
The timing accuracy of the measurements performed by the Chrono methods
commands depends on the number of electrochemical signals sampled during
the measurement. Sampling more than one electrochemical signal reduces the
number of measurable data points.
5 – Using steps and levels
There are two types of basic items that can be used in the Chrono methods editor
window to build the required sequence of steps for command: steps and levels. This
section provides more information on the Level item.
A Level is identical to a step except that it does not have a Potential (or Current)
parameter. This means that the level will record the electrochemical signals with a
given interval time and duration, without changing the applied potential or current.
This provides the user with a useful tool to sample the same electrochemical
response but with different interval times.
Open the Chrono methods editor window, select the last step of the sequence and
add a level to the sequence (see Figure 32).
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Figure 32 – Adding a level to the sequence
Click the level that was added to the sequence to display the parameter details in
the frame on the right (see Figure 18).
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Figure 33 – The details of the level parameters are displayed in the frame on the right
Note
The parameters of the Level are grouped in two sections: basic and advanced.
The level has the following default basic parameters:
•
•
•
•
•
Text: Step
Duration (s): 0.001
Sample: Yes
Interval time (s): 0.0001
Number of points: 10
Warning
The maximum duration for a single step or level is 4294 seconds.
The two additional parameters, Pre Autolab control and Post Autolab control, are
advanced settings that can be used to change the Autolab settings during the
sequence. These parameters are available in the advanced section and their use falls
outside of the scope of this tutorial.
Change the duration to 0.010 s and the interval time to 0.001 s. This will extend
the sequence by 10 ms without modifying the applied potential. During this extra
time, the electrochemical signals will be sampled using an interval time of 1 ms.
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Click the OK button to close the editor window and update the procedure editor
(see Figure 34).
Figure 34 – The updated procedure editor
The procedure editor now indicates that the total duration is 0.025 s and that the
number of points is 160. The extra level that was added to the sequence increases
the measurement time by 10 ms, but since it uses a larger interval time, the total
number of points is increased by only 10 points.
5.1 – CM Tutorial – Example 3
Select the CM Tutorial – Example 3 procedure from the Standard group. Connect
the dummy cell (c) to the instrument and start the measurement. The procedure will
perform a measurement similar to the measurement used in the Example 1, but with
an extra level at the end of the measurement:
•
•
•
•
Step 1 – setpoint 0 V, duration 0.005 s, interval time 0.0001 s.
Step 2 – setpoint 0.3 V, duration 0.005 s, interval time 0.0001 s.
Step 3 – setpoint -0.3 V, duration 0.005 s, interval time 0.0001 s.
Level – no setpoint, duration 0.01 s, interval time 0.001 s.
Only the WE(1).Potential is measured during this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 35 shows the expected potential profile for this
measurement on the dummy cell. A combi plot is used to emphasize the change in
sampling rate for the level.
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Figure 35 – The potential (blue curve) profile plotted vs Corrected time measured during the
Example 3 procedure (the data is displayed at the end of the measurement)
The potential profile shown in Figure 35 displays the data points collected during
the final level in blue. The whole measurement consists of a single data set, but the
final part was measured using a larger interval time than the initial part of
measurement. The level does not have a setpoint parameter and therefore, there is
no potential change between the third step of the sequence and the level.
Figure 36 shows a practical example of a chrono amperometry measurement using
a level in combination with a step to change the sampling rate. The second step in
the experiment is followed by a level with a larger interval time. As the current
becomes mass-transport limited, it is not useful to measure the electrochemical
response of the cell with a small interval time.
Note
Using different interval times to record the electrochemical response of the cell
is sometimes referred to as decimation or downsampling.
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Figure 36 – An example of a measurement using a combination of steps and levels to reduce
the number of data points
6 – Switching off the sampler
An additional feature of the Chrono methods command is that the sampler can be
switched off during the sequence. By default, the sampler is on for each basic
element in a sequence. However, the user has the choice to switch the sampler on
or off for each element in the sequence. This is useful if only a part of the
measurement is of interest.
Open the Chrono methods window and select the second step. In the parameters
frame, change the Sample status from Yes to No (see Figure 37).
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Figure 37 – Changing the sample status from Yes to No for the second step
Changing the sampling status of the second step sets the estimated number of
points to 0. The interval time parameter is also greyed out and cannot be edited
anymore.
6.1 – CM Tutorial – Example 4
The CM Tutorial – Example 4 procedure illustrates this option. Select this procedure
from the standard group, connect the dummy cell (c) to the instrument and start
the measurement.
Only the WE(1).Potential is measured during this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 38 shows the potential profile corresponding to this
measurement.
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Figure 38 – The potential (blue points) profile plotted vs Corrected time measured during the
Example 4 procedure (the data is displayed at the end of the measurement)
Comparison between Figure 38 and Figure 35 clearly shows that the data from the
second step of the sequence is missing. Since nothing is sampled during this step,
no potential value is available for plotting. However, the timing of the other
elements of the sequence is not affected, since the last step and the following level
are correctly located on the time scale.
Note
Although the second step of the sequence was not sampled in this experiment,
the potential of this step was nonetheless applied to the electrochemical cell. The
analysis view cannot show this in the plot because sampling was switched off
during this step. However, connecting an oscilloscope to the Eout connector of
the potentiostat clearly shows that the second step is applied during the
measurement (see Figure 39).
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Example 4
V
0.5
Step 2
unsampled
0.4
0.3
Cell off
0.2
0.1
0.0
-0.1
Step 1
Step 3
Level
-0.2
-0.3
25 ms
-0.4
-0.5
-10
-5
0
5
10
Time
15
20
25
30
35
ms
40
Figure 39 – Oscilloscope trace measured on the E out connector of the potentiostat showing
the applied potential during the measurement of Example 4 (time axis has arbitrary offset)
7 – Using Repeat (unsampled) and Repeat
There are two types of advanced items that can be used in the Chrono methods
editor window to build the required sequence of steps for the Chrono methods
command: Repeat (unsampled) and Repeat.
Inserting any one of these two items in the sequence editor creates a new subsequence in which new items can be inserted.
The main difference between Repeat (unsampled) and Repeat is that the items
located in the first sequence are not sampled during the measurement.
To add a Repeat (unsampled) item to the sequence, select the last item in the
sequence and click the
button. Select the Repeat (unsampled) item from the
popout menu (see Figure 40).
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Figure 40 – Inserting a Repeat (unsampled) item creates a new sequence in the editor
A new item will be added to the sequence (see Figure 41).
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Figure 41 – The Repeat (unsampled) item creates a new sequence
Any item added to the Repeat (unsampled) sequence will be applied but not
sampled during the measurement. This provides a framework for introducing a preor a post-conditioning of the electrode during a measurement and for reducing the
total number of points during long measurements.
Note
The Repeat (unsampled) sequence is a useful tool for experiments in which a
sequence of steps is repeated many times. Instead of sampling every step, which
would generate a lot of data points, the user may prefer to sample only a few
steps every now and then (for example two steps every twenty steps).
Using the same approach as in the previous examples, select the Repeat (unsampled)
item and add two steps using the
button (see Figure 42).
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Figure 42 – Adding two steps to the Repeat (unsampled)
Note
The Steps added to the Repeat (unsampled) have the sample status set to No by
default. The interval time parameter is greyed out and the estimated number of
points is set to 0. It is possible to overrule the sample status, if necessary.
Change the potential of the first step of the Repeat (unsampled) sequence to 0.5
and the potential of the second step to -0.5. Change the duration of both steps to
0.010 s (see Figure 43).
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Figure 43 – Adjusting the parameters of the two steps
In this example, the Repeat (unsampled) are intended to be used as a
preconditioning stage. Therefore, the whole sequence has to be placed before the
three steps and the level of the measurement sequence.
Select the Repeat (unsampled) item in the sequence to highlight the whole subsequence (see Figure 44).
Note
The two Steps located inside the Repeat (unsampled) are also highlighted in dark
grey, indicating that these Steps belong to the selected Repeat (unsampled) item.
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Figure 44 – Select the Repeat (unsampled) item in the sequence
To move this sequence up, click the
the left-hand side (see Figure 44).
Figure 45 – Click the
Click the
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button in the small toolbar in the frame on
button to move the selected sub-sequence up in
button four times to move it all the w ay at the top of the sequence.
NOVA Chrono methods tutorial
Select the Repeat (unsampled) and change the number of repetitions to 10. The
duration will be updated (see Figure 46).
Figure 46 – Setting the number of repetitions to 10 for the whole Repeat (unsampled)
sequence
Click the OK button to close the sequence editor window. The procedure editor will
be updated with the new values (see Figure 47).
Figure 47 – The updated procedure editor
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Note
The total number of points does not increase compared to the example shown
in Figure 34 because the Repeat (unsampled) does not sample any data points.
The number of commands in the sequence is 5: the procedure editor displays the
number of items in the main sequence (3 steps, 1 level and 1 Repeat
(unsampled)). The total measurement time is updated taking the ten repetitions
of the two steps in the Repeat (unsampled) sequence into account.
7.1 – CM Tutorial – Example 5
The CM Tutorial – Example 5 procedure illustrates this option. Select this procedure
from the standard group, connect the dummy cell (c) to the instrument and start
the measurement.
Only the WE(1).Potential is measured during this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 48 shows the potential profile corresponding to this
measurement.
Figure 48 – The potential (blue curve) profile plotted vs Corrected time measured during the
Example 5 procedure (the data is displayed at the end of the measurement)
The potential profile shown in Figure 48 is identical to the potential profile shown
in Figure 35. The reason for this is that nothing is sampled during the Repeat
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(unsampled) sequence and the time is only logged when the sampler is collecting
data points. Therefore, the Corrected time scale shown in both plots is the same.
Note
The total time of the experiment is about 225 ms, while the corrected time scale
is only 25 ms. The corrected time scale is based on the first measured data point.
Since the steps located in the Repeat (unsampled) sequence are not sampled, the
corrected time scale does not include these unsampled steps.
The steps located in the Repeat (unsampled) sequence were indeed applied during
the measurement. This can be shown by connecting an oscilloscope to the Eout
connector of the potentiostat (see Figure 49).
V
1.0
Example 5
0.8
Step 1
Step 2
Repeat (unsampled)
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-1.0
-25
Level
Step 3
-0.8
0
25
50
75
Time
100
125
150
175
200
ms
225
Figure 49 – Oscilloscope trace measured on the E out connector of the potentiostat showing
the applied potential during the measurement of example 5. Ten repetitions of the
conditioning collection are applied before measurement is started (time axis has arbitrary
offset)
Click the
Figure 50).
button to remove the complete Repeat (unsampled) sequence (see
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Figure 50 – Click the
button to remove the highlighted item from the sequence
If a Repeat sequence is used instead of a Repeat (unsampled) sequence, the same
behaviour is observed. The Repeat item creates a new sequence to which new items
can be added (see Figure 51).
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Figure 51 – Inserting a Repeat item creates a new sequence in the editor
Items added to the Repeat sequence will be sampled during the measurement.
Add two steps to the measurement Repeat sequence and change the potential of
the first step to 0.5 V and the potential of the second step to -0.5 V. Change the
duration of both steps to 0.010 s and the interval time to 0.001 s (see Figure 52).
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Figure 52 – Editing the two steps added to the Repeat sub-sequence
Note
The steps located in the Repeat have the sample status set to on by default. This
status can be overruled, if necessary.
Set the number of repeats to 1. Click OK to close the chrono methods editor.
Click the OK button to close the sequence editor window. The procedure editor will
be updated with the new values (see Figure 53).
Figure 53 – The updated procedure editor
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Note
The total number of points increases compared to the previous example (see
Figure 47) because the Recurrent steps sequence records data points using the
defined sampler. The number of commands in the total sequence is five: three
steps, one level and one recurrent steps sequence.
7.2 – CM Tutorial – Example 6
The CM Tutorial – Example 6 procedure illustrates this option. Select this procedure
from the standard group, connect the dummy cell (c) to the instrument and start
the measurement.
Only the WE(1).Potential is measured during this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 54 shows the potential profile corresponding to this
measurement.
The CM Tutorial – Example 6 procedure uses this particular sequence. Select this
procedure from the standard group, connect the dummy cell (c) to the Autolab and
press the start button. When the measurement is finished, inspect the measured
data points in the analysis view. Figure 54 shows the potential profile recorded
during this measurement.
Figure 54 – The potential (blue curve) profile plotted vs Corrected time measured during the
Example 6 procedure (the data is displayed at the end of the measurement)
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Since the two final steps are located in a Repeat sequence, they are sampled during
the measurement.
7.3 – CM Tutorial – Example 7
The CM Tutorial – Example 7 uses the same sequence as in the Example 5, but
instead of using a Repeat (unsampled) sequence, a Repeat sequence is used. Select
this procedure from the standard group, connect the dummy cell (c) to the
instrument and start the measurement.
Only the WE(1).Potential is measured during this experiment.
Press the start button to run the measurement. Like in the previous example, a
message box is used at the beginning of the measurement.
When the measurement is finished, the measured data points will be displayed in
the measurement view. Figure 55 shows the potential profile corresponding to this
measurement.
Figure 55 – The potential (blue curve) profile plotted vs Corrected time measured during the
Example 7 procedure (the data is displayed at the end of the measurement)
The potential profile shown in Figure 55 is the same as the profile recorded on the
Eout connector of the potentiostat, shown in Figure 49. This illustrates the difference
between the unsampled and a normal Repeat sequence in the Chrono methods
command.
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