The Data Curve

In the sample data file, the data portion of the file begins with this line.

CURVE TABLE 200

The tag identifies the data set as a TABLE data type, and identifier of CURVE, and with 200 data points. Other tag identifiers are possible. The 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 data type is a set of descriptive column headings. These headings are for file readability only. The DC Corrosion analysis scripts do not use the column headings to identify data positions within the curve. Click on each heading to get a description.

PtThe numbers in this first column, under the column label "Pt", are data-point numbers. As is typical in computer programs, DC105 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 typical DC105 data file are always sequential integers. Data that have been edited 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. (#) TThis column is time. The unit for time is seconds. Time is always reported in the data file, even if it is not the independent variable in a experiment. All the standard DC105 techniques yield data points evenly spaced in time. However, the data analysis functions work on data even when the data points are not recorded at uniformly separated times. (s) VfPotential: Vf, Vu, Vm These columns are cell potentials. The units are volts. Vf In controlled-current techniques Vf is a value you measure. 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 you select IR Compensation, 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 before 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 you select IR Compensation (current interrupt), 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. (V) ImThis column is the cell current. The unit is the ampere. Im is always a measured quantity. The DC105 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. (A) VuPotential: Vf, Vu, Vm These columns are cell potentials. The units are volts. Vf In controlled-current techniques Vf is a value you measure. 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 you select IR Compensation, 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 before 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 you select IR Compensation (current interrupt), 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. (V) SigThis 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. (V) AchThis column is the potential measured using the auxiliary A/D converter input. The unit is the volt. (V) IERange (#) Over (bits)
0 0.999 -4.980E-001 -2.064E-004 0.000E+000 -5.000E-001 1.543E+000 7 .............
1 1.999 -4.490E-001 -1.569E-004 0.000E+000 -4.500E-001 1.543E+000 7 .............
2 2.999 -3.980E-001 -1.318E-004 0.000E+000 -4.000E-001 1.543E+000 7 .............
3 3.999 -3.490E-001 -1.136E-004 0.000E+000 -3.500E-001 1.543E+000 7 .............