The Data Curve

With most Electrochemical Energy data files, the data portion of the file begins with this line:

CURVE TABLE 92

The tag identifies the data set as a TABLE datatype, and identifier of CURVE, and with 92 data points. Other tag identifiers are possible. The Electrochemical Energy software uses the CURVE tag, or close variants for most of its standard techniques. Some TABLE types do not specify the number of data points. This number is not required.

The first line following the datatype is a set of descriptive column headings. These headings are for file readability only. The Electrochemical Energy analysis scripts do not use the column headings to identify data positions within the curve. Click each heading to get a description. The table shown below is typical of most Electrochemical Energy data files with the exception of Cyclic Charge Discharge files.

Pt¹The numbers in this first column, under the column label “Pt”, are data point numbers. As is typical in computer programs, Electrochemical Energy data-point numbering starts with zero, not one. The first data point recorded is stored as the “zeroth” point.
The data point numbers for a normal Electrochemical Energy data file are always sequential integer. Edited data can have gaps in the point-number sequence. This creates no problems in the data analysis. If you write your own data manipulation program, we recommend that you also allow for non-sequential point numbers. T²‘This column is time. The times are in seconds. Time is always reported in the data file, even if it is not the independent variable in a experiment. All the standard Electrochemical Energy techniques yield data points evenly spaced in time. However, the data analysis functions work on data where this is not the case. Vf³These columns are cell potentials. The units are volts. Vf In controlled current techniques Vf is a measured number. If you select IR Compensation, the number is corrected for the IR-drop measured via current-interruption. The size of the correction is reported in the Vu data column. Vu is commonly referred to as the uncompensated voltage.
In controlled potential techniques, Vf is the corrected, measured cell voltage. Any external voltage added to the cell excitation via the external input connector is included in this value. If IR Compensation has been selected, the actual applied voltage between current interruptions is the sum of the Vf and Vu data
In Corrosion Potential measurements, or in the Open Circuit Voltage (OCV) measurement prior to an experiment, Vf is the filtered, measured, open circuit voltage. A digital filter has been applied to minimize pickup of the AC mains frequency (50 or 60 Hz).
Vu – Vu is commonly referred to as the uncompensated voltage. It is the voltage drop across the solution resistance between the Working Electrode and the tip of the Reference Electrode. If IR Compensation (Current Interrupt) has been selected, Vu is the difference between the measured voltage with the current flowing, and the voltage during the period of the Current Interrupt. The actual applied voltage between current interruptions is the sum of the Vf and Vu data.
Vm Vm, where it appears, is included only for compatibility with older versions of the Gamry Framework Software. Im⁴This column is the cell current. The unit is the ampere. Im is always a measured quantity. The Electrochemical Energy software follows the anodic current-sign convention. An anodic current arises from an oxidation (corrosion) occurring at the electrode connected to the potentiostat’s working electrode (green) lead. It is represented by a positive value. Both analog and digital filters may have been applied to the measured current signal. The nature and degree of the filtering is determined by the Explain script used to run the experiment. It is generally indicated in the Hardware parameters section of the data file.
In controlled-potential techniques, the Framework autoranges the I/E converter of the potentiostat to try to keep the A/D converter between 8% to 90% of its full-scale range. The range used for a current measurement cannot be recovered from the Im value. It is listed in the column labeled IERange In controlled-current techniques, Im is also the measured cell (excitation) current. Any external signal added to the cell excitation via the external input connector is reflected in the current values shown in this column. Vf⁵These columns are cell potentials. The units are volts.
Vf In controlled current techniques Vf is a measured number. If you select IR Compensation, the number is corrected for the IR-drop measured via current-interruption. The size of the correction is reported in the Vu data column. Vu is commonly referred to as the uncompensated voltage.
In controlled potential techniques, Vf is the corrected, measured cell voltage. Any external voltage added to the cell excitation via the external input connector is included in this value. If IR Compensation has been selected, the actual applied voltage between current interruptions is the sum of the Vf and Vu data.
In Corrosion Potential measurements, or in the Open Circuit Voltage (OCV) measurement prior to an experiment, Vf is the filtered, measured, open circuit voltage. A digital filter has been applied to minimize pickup of the AC mains frequency (50 or 60 Hz).
Vu is commonly referred to as the uncompensated voltage. It is the voltage drop across the solution resistance between the Working Electrode and the tip of the Reference Electrode. If IR Compensation (Current Interrupt) has been selected, Vu is the difference between the measured voltage with the current flowing, and the voltage during the period of the Current Interrupt. The actual applied voltage between current interruptions is the sum of the Vf and Vu. Vm, where it appears, is included only for compatibility with older versions of the Gamry Framework Software. Pwr⁶This column is the Power. The unit is watts. This column is calculated by the Gamry Framework during data acquisition (Current x Voltage)
This column is not present in Cyclic Voltammetry curve. Sig⁷This column is the output of the signal generator and the input to the control amplifier. The units are in volts (V). In potentiostatic techniques the applied cell voltage should be the same as this signal. This column of data also takes into account the uncompensated voltage.
In galvanostatic techniques the applied current is proportional to this signal. The proportionality constant depends upon the potentiostat and the current range in use. Ach⁸This column is the potential measured using the auxiliary A/D converter input. The unit is the volt. Temp⁹This column is the temperature measured if a thermocouple is attached. For Cyclic Charge Discharge data files, the temperature is recorded at the beginning (Tstart) and end (Tend) of each step.
If no thermocouple is attached, these columns show all zeros.
This column is not present in Cyclic Voltammetry and Read Voltage IERange¹⁰This column indicates the hardware current-range used to collect the data point. If the number in the column is n, then the range used is given by fs x 10^n pA. fs depends on the maximum current range of the Potentiostat (See Table.) A value of n of 5 would represent the 6 x 10^5 pA range (600 nA range) for a Reference 600. Potentiostat fs Reference 600 6 Over

# s V A V W V V deg C # bits

0 .5 1.03351E+001 1.49896E-001 0.00000E+000 1.54919E+000 1.49772E+000 7.70412E-001 0.00000E+000 11 ………..

1 1 1.04738E+001 1.49896E-001 0.00000E+000 1.56998E+000 1.49774E+000 7.80825E-001 0.00000E+000 11 ………..

2 1.5 1.06113E+001 1.49897E-001 0.00000E+000 1.59061E+000 1.49774E+000 7.91136E-001 0.00000E+000 11 ………..

3 2 1.07473E+001 1.49894E-001 0.00000E+000 1.61095E+000 1.49774E+000 8.01342E-001 0.00000E+000 11 ………..

AE Data

If an experiment was run using an instrument with the Auxiliary Electrometers option, the resulting data file may contain additional columns for AE data. These columns are only present in the data file if AE data were recorded. During experiment setup, you may specify which AE channels are to be recorded. AE columns in the data file for channels that were not selected contain all zeros. The experimental setup page also shows which AE channels were selected. If one or more channels were selected, a total of sixteen additional columns appear in the data file after the Over column: eight columns containing voltage for each AE channel and eight columns for power.

Column headings for AE data are: Vf1 through Vf8 and Pwr1 through Pwr8.

Cyclic Charge Discharge Data Curves

Data files produced by Cyclic Charge Discharge experiments have a different format than other Electrochemical Energy experiments. The data table typically has an identifier of CAPACITYCURVE and the columns differ as well. The table shown below is typical of a Cyclic Charge Discharge Data file.

Pt¹¹The numbers in this first column, under the column label “Pt”, are data point numbers. As is typical in computer programs, Electrochemical Energy data-point numbering starts with zero, not one. The first data point recorded is stored as the “zeroth” point. The data point numbers for a normal Electrochemical Energy data file are always sequential integer. Edited data can have gaps in the point-number sequence. This creates no problems in the data analysis. If you write your own data-manipulation program, we recommend that you also allow for non-sequential point numbers T¹²This column is time. The times are in seconds. Time is always reported in the data file, even if it is not the independent variable in a experiment. All the standard Electrochemical Energy techniques yield data points evenly spaced in time. However, the data analysis functions work on data where this is not the case. Type¹³This column indicates whether the row of data represents a charge step or discharge step.0 represents a charge. 1 represents a discharge.The combination of a charge step and a discharge step represent one cycle in a cyclic charge-discharge data table.Cycle ¹⁴This column is the cycle number. Because a cycle is composed of one charge step and one discharge step, each cycle is represented by two rows of data.Charge ¹⁵This column is the charge. The units is Coulombs. The values for this column are calculated by the Gamry Framework during data-aqcuisition.NOTE: This column is always recorded in Coulombs, however, the Analyst can display it in ampere-hours or user-defined custom units depending on the current option settings. (See script-specific options.)Duration ¹⁶This column represents the duration of the step. The unit is seconds.Vstart ¹⁷These two columns represent the voltages at the beginning (Vstart) and end (Vend) of each step. The units are volts.Vend ¹⁸These two columns represent the voltages at the beginning (Vstart) and end (Vend) of each step. The units are volts./¹⁸Energy ¹⁹This column is the energy. The unit is joules. This column is calculated by the Gamry Framework during data acquisition.NOTE: The energy is always recorded by the Gamry Framework in joules, however, the Analyst can display it in watt-hours or user-defined custom units depending on the current option settings. (See script-specific Options.)Tstart ²⁰This column is the temperature measured if a thermocouple is attached. For Cyclic Charge-Discharge data files, the temperature is recorded at the beginning (Tstart) and end (Tend) of each step.If no thermocouple is attached, these columns show all zeros.This column is not present in Cyclic Voltammetry and Read Voltage curves.Tend ²¹This column is the temperature measured if a thermocouple is attached. For Cyclic Charge-Discharge data files, the temperature is recorded at the beginning (Tstart) and end (Tend) of each step.If no thermocouple is attached, these columns show all zeros.This column is not present in Cyclic Voltammetry and Read Voltage curves. Over

# s # # C s V V J deg C deg C bits

0 .5 0 1 5.218961 41.50167 11.46985 18.33774 82.07176 0.8555219 1.371079 ………..

1 1 1 1 5.158938 34.38833 16.97445 8.048766 -64.02049 1.2696 .6002461 ………..

2 1.5 0 2 5.790366 45.00167 16.97445 18.3363 87.97629 0.77017 1.371029 ………..

3 2 1 2 5.16302 34.415 10.335 8.051501 -64.06015 1.269403 .6004817 ………..

AE Data for Cyclic Charge Discharge

IF AE data were recorded for a Cyclic Charge Discharge experiment, the data file includes 24 additional columns. These columns contains the starting voltage, ending voltage, and energy for each AE channel. If data were not recorded for an AE channel, the columns for that channel contain all zeros. The experimental setup page shows which channels were selected.

Column headings for AE data are: Ch1 Vstart through Ch8 Vstart, Ch1 Vend through Ch8 Vend, and Ch1 Energy through Ch8 Energy.