electrochem: Electrochemistry data parser

The electrochem parser handles the reading and processing of files from BioLogic’s EC-Lab, namely the binary .mpr files and the .mpt ASCII data files.

Note

This interface is not yet final and will change with version 5.0.0

.mpt files are made up of a header portion (with the technique parameter sequences and an optional loops section) and a tab-separated data table.

.mpr files are structured in a set of “modules”, one concerning settings, one for actual data, one for logs, and an optional loops module. The parameter sequences can be found in the settings module.

The basic function of the parser is to:

1. Read in the technique data and create timesteps.

2. Collect metadata such as the measurement settings and the loops contained in a given file.

3. Collect common data describing the technique parameter sequences.

These are the implemented techniques for which the technique parameter sequences can be parsed:

CA	Chronoamperometry / Chronocoulometry
CP	Chronopotentiometry
CV	Cyclic Voltammetry
GCPL	Galvanostatic Cycling with Potential Limitation
GEIS	Galvano Electrochemical Impedance Spectroscopy
LOOP	Loop
LSV	Linear Sweep Voltammetry
MB	Modulo Bat
OCV	Open Circuit Voltage
PEIS	Potentio Electrochemical Impedance Spectroscopy
WAIT	Wait
ZIR	IR compensation (PEIS)

Usage

The use of electrochem can be specified using the "parser" keyword in the schema. Further information can be specified in the "parameters" (dict):

• "filetype" (str): The file type of the raw data file. See here for details.

Provides

The electrochem parser loads all the columns present in an .mpt or .mpr file.

Note

.mpt files can contain more data than the corresponding binary .mpr file.

Most techniques write data that can be understood as a series of timesteps. Each timestep provided by the parser has the following format:

- fn   !!str
- uts  !!float
- raw:
    "{{ col1 }}":  !!int
    "{{ col2 }}":
      {n: !!float, s: !!float, u: !!str}

For impedance spectroscopy techniques (PEIS, GEIS), the data is made up of spectroscopy traces. The data is thus split into traces by the column "cycle number" and cast into a single timestep. Each trace now corresponds to a spectroscopy scan, indexed by "cycle number" / "trace_number". The timestep takes the following format:

- fn   !!str
- uts  !!float
- raw:
    traces:
      "{{ trace_number }}":
        "{{ col1 }}":
            [!!int, ...]
        "{{ col2 }}":
            {n: [!!float, ...], s: [!!float, ...], u: !!str}

Note

The parsed data can contain infinities (i. e. float("inf") / float("-inf")). While datagrams containing NaN and Inf can be exported and read back using python’s json module, they are not strictly valid jsons.

TODO

https://github.com/dgbowl/yadg/issues/10

Current values of the uncertainties "s" are hard-coded from VMP-3 values of resolutions and accuracies, with math.ulp(n) as fallback. The values should be device-specific, and the fallback should be eliminated.

TODO

https://github.com/dgbowl/yadg/issues/11

The “raw” data in electrochemistry files should only contain the raw quantities, that is the control_I or control_V and the measured potentials Ewe, Ece or the measured current I. Analogous quantities should be recorded for PEIS/GEIS. All other columns should be computed by yadg.

The "metadata" collected from the raw file will depend on the "filetype". For both .mpt and .mpr the `"metadata" will contain a "settings" and a "params" field:

The "settings" field for parsed ".mpt" files contains the technique name, a posix timestamp and the raw header lines as found in the file. The "settings" from parsed ".mpr" files contain the technique and more explicitly parsed information than from ".mpt" files, like the “cell characteristics” specified in EC-Lab.

The "params" will contain the technique parameter sequences and the keys in each sequence will be the same independent of "filetype" but an (int): value in the .mpr "params" may be a (str): when parsed from the corresponding .mpt since the mapping has not yet been reverse engineered.

TODO

https://gitlab.empa.ch/krpe/yadg/-/issues/13

In .mpr files, some technique parameters in the settings module correspond to entries in drop-down lists in EC-Lab. These values are stored as single-byte values in .mpr files.

The metadata from parsed ".mpr" files also provides the "log" which contains more general parameters, like software, firmware and server versions, channel number, host address and an acquisition start timestamp in Microsoft OLE format.