Multiplexed EFM Trend - Setup Parameters

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Multiplexed EFM Trend - Setup Parameters

Description

 

3 - Multiplexed EFM Trend

 

Parameter

Description

Units

Pstat

Select the potentiostat/galvanostat to perform the experiment. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used.

 

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Only potentiostats that are paired with a Multiplexer can be selected.

 

Channel

There is one Channel Setup switch for each of the 8 channels. Click the checkbox to select a specific channel. As the script loops through the channels, it only runs tests on channels that are selected. The selected channel numbers do not have to be continuous.

 

Identifier

A string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs.

 

The Channel Identifier string is virtually identical to the Test Identifier string. The only difference is that in multiplexed tests, the Identifier refers to an experiment run on a single cell and not to the entire experimental run.

 

System

Select a set of electrochemical parameters relevant to your particular test system. The parameters are recovered from the system parameter database file. The recovered parameters are all used for the calculation of the corrosion rate. They are the sample's equivalent weight, density, anodic β and cathodic β. When you attempt to run an experiment, the system searches the SYSTEM.SET file for a parameter set stored under the name in the System parameter. If the software finds no parameter set, an error message appears and you are returned to the Setup dialog box.

 

Area

The electrode area that is used in calculations. It can be set individually for each channel.

 

Notes

Enter several lines of text that describe the experiment. There is a separate entry for each channel in a multiplexed test. A typical use of Channel Notes is to record the experimental conditions for a data set.

 

The Channel Notes controls are similar to the Notes control described for non-multiplexed experiments.

 

Base Filename

Each channel has its own data file. The Base Filename is used to derive the filenames for these files. The filename for Channel N (1–8) is created by appending the character N to the Base Filename, then adding a *.DTA filename extension.

 

If the Base Filename is MYMUXDATA, the data file for Channel 1 is named MYMUXDATA1.DTA. The filename resulting from the concatenation of the Base Filename and the channel number must adhere to Windows® filename conventions. Avoid punctuation characters (the underscore, "_", is OK). You are allowed a maximum of 250 (not 255) characters in the Base Filename. The extra characters are reserved for the channel number appended to the Base Filename. Do not include *.DTA when specifying the Base Filename. It is automatically added when the full data file name is generated.

 

Save Raw Data

If enabled, individual Electrochemical Frequency Modulation data files are recorded and saved in addition to the Electrochemical Frequency Modulation Trend data file.

 

The file names of the raw data files consist of the main file's name, followed by an underscore and the repeat number in which the data was recorded.

 

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The format of these raw data files is identical to those created by the Electrochemical Frequency Modulation experiments and use the same analysis routines when opened in the Gamry Echem Analyst 2™.

 

Base Freq.

The repeat time of the EFM waveform applied to the cell. The two frequencies simultaneously applied to the cell are:

 

 

hertz (Hz)

Multiplier A

Multiplier A and Multiplier B define the EFM waveform applied to the cell. The two frequencies simultaneously applied to the cell are:

 

 

 

Multiplier B

 

Amplitude

The amplitude of each of the two sine waves. Keep in mind that the total EFM waveform amplitude typically ranges between 1 and 2 times of the selected value due to the principle of superposition.

 

Choose an amplitude that is small compared to the Tafel constants but large enough to give a reasonable signal. For many systems, 10 to 40 mV is a good starting point.

mV

DC Voltage

The constant potential applied to the cell throughout the EFM scan. For most EFM experiments, the DC Voltage is 0 V versus the open-circuit potential

volts (V)

Cycles

The number of times the scan is repeated during the experiment.

 

The Number of Cycles and the Base Frequency determine the duration of an EFM experiment. The greater the cycle number, the longer the experiment takes, but the resolution between the peaks of the intermodulation spectrum increases. Although you may enter any number of cycles, you get better results if Number of Cycles has a power of two: 2, 4, 8, ... 128, with a maximum number of 255. The first repetition of the Base Frequency (the first cycle) is not used for data analysis. The duration of an EFM experiment can be calculated as follows:

 

 

I/E Range Mode

Select the current range mode and choose between Auto mode or Fixed mode.

 

Because the EFM waveform is a complicated AC waveform, better results are generally obtained in the Fixed mode. In Fixed mode, the current scale is selected based on Max Current. In Auto mode, Max Current is used as an initial guess for the proper scale, but subsequent decisions are based on the value of the most recently measured current.

 

Max Current

Max Current controls the current measurement range if I/E Range is set to Fixed mode. If I/E Range is set to Auto mode, Max Current specifies the maximum expected starting current.

 

The software adjusts the current range based on the Max Current input. In order to use the most sensitive range that will not overload, the software chooses the current range based on a value that is 89% of the full-scale current range.

 

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The Max Current parameter is a current, not a current density.

 

If your current data look very choppy and stepped, the problem could be a poorly selected current range. If you enter a Max Current value of 10 mA and the maximum current in your sweep is only 100 mA, you are only using 1/100th of the potentiostat's A/D converter range. The result is a significant quantization error. Rerun the test entering a smaller Max Current value.

 

If your current data show perfectly flat and horizontal regions, the current has most likely overloaded the potentiostat's current-measurement circuits. Check that the value that you entered for the Max Current parameter is larger than the actual measured cell current. Try rerunning the test with a larger value for the Max Current.

mA

Conditioning

You may condition the electrode as the first step of the experiment, e.g., to remove an oxide film from the electrode or to grow one. Conditioning ensures that the metal sample has a known surface state at the start of the experiment. This step is done potentiostatically for a set amount of time.

 

Turn the conditioning phase On or Off with the Conditioning switch check box. Conditioning E is the potential applied during the conditioning phase of the experimental sequence. The conditioning potential has an allowed range of ±8 V. The resolution is 0.25 mV. If you have iR-compensation enabled for the data acquisition phase of your experiment, it is also turned on during conditioning. Conditioning E is always specified vs. Eref, because the open-circuit potential is not measured until after Conditioning is completed.

 

The Conditioning Time is the length of time that the sample is potentiostatted at Conditioning E. The minimum time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

seconds (s), volts (V)

Init. Delay

The Initial Delay phase of the experiment is the first step to occur in the experimental sequence. This phase of the experiment stabilizes the open-circuit potential of the sample prior to any applied signal and measures that open-circuit potential.

 

The Initial Delay is turned On or Off via the check box in the Setup dialog. The Initial Delay Time parameter is the time that the sample is held at the open-circuit potential prior to the scan. The delay may stop before the Initial Delay Time if the Stability criterion for Eoc is met. The minimum Delay Time time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

 

In many cases, you really do not want to set a delay for a fixed time, but you may want to a delay until Eoc stops drifting. The Stability parameter allows you to set a drift-rate that you feel represents a stable Eoc. If the absolute value of the drift-rate falls below the Stability parameter, the Initial Delay phase of the experiment ends immediately, disregarding the programmed Initial Delay Time. Enter a Stability setting of zero to ensure that the delay will last for the full Initial Delay Time. A typical value is 0.05 mV/s. The upper limit of this parameter is 8 V/s, well above the range of practical stabilities with real cells, while the lower limit is set by your patience. A stability of 0.01 mV/s indicates a drift of less than 1 mV within 100 seconds. The software will always take data long enough to resolve a 1 mV change in the potential at the requested drift rate.

 

No open-circuit voltage measurement occurs if the initial delay is turned off. In this case, the open-circuit voltage defaults to 0.0 V.

seconds (s), mV/s

Corrosion Type

The calculation of the corrosion current from EFM data depends on the mechanism of the corrosion process. The three choices are Active, Diffusion control, and Passive film control. The choice here only determines the equation for the run-time display. You may change your choice later in the Echem Analyst 2™ and recalculate the corrosion rate without having to rerun the experiment.

 

Corr. Rate Units

Select the unit of the corrosion rate displayed. Choose between mpy (mils/year) or mmpy (mm/year).

 

Repeat Time

The time (specified as hours:minutes) between each test on the cell. For example, if the first test begins at 2:08 and the Repeat Time is 30 minutes, additional tests occur at 2:38, 3:08, 3:38, etc.

 

Enter fractional minutes as decimal numbers. The Repeat Time must be longer than the time required to run a single EFM measurement. When you click the OK button from the Setup dialog box, the script estimates the time required to run a single EFM measurement. If this time is close to or longer than the entered Repeat Time, Framework™ opens an error box and returns to the Setup.

minutes (min)

Total Time

The duration of the experimental run. The script keeps track of the elapsed time from the start of the experiment. At the start of each test, the elapsed time is compared to the Total Time. If the elapsed time is greater than or equal to the Total Time, the experiment is halted and the Runner window is closed.

 

The Total Time is always entered in hours. Fractional hours can be entered as decimal numbers. To run a single test, enter a Total Time equal to the Repeat Time or simply run the Electrochemical Frequency Modulation experiment. For N tests, enter a Total Time = N × Repeat Time.

 

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A Total Time of zero results in no tests being run.

hours (hr)