Load sEIT data from .ctr files (volt.dat files readable by CRTomo,
        produced by CRMod)

        Parameters
        ----------
        data_dict : dict
            Data files that are imported. See example down below

        Examples
        --------

        >>> import glob
            data_files = {}
            data_files['frequencies'] = 'data/frequencies.dat'
            files = sorted(glob.glob('data/volt_*.crt'))
            data_files['crt'] = files

def load_data_crt_files(self, data_dict):
        """Load sEIT data from .ctr files (volt.dat files readable by CRTomo,
        produced by CRMod)

        Parameters
        ----------
        data_dict : dict
            Data files that are imported. See example down below

        Examples
        --------

        >>> import glob
            data_files = {}
            data_files['frequencies'] = 'data/frequencies.dat'
            files = sorted(glob.glob('data/volt_*.crt'))
            data_files['crt'] = files

        """
        if isinstance(data_dict, str):
            raise Exception('Parameter must be a dict!')

        frequency_data = data_dict['frequencies']
        if isinstance(frequency_data, str):
            frequencies = np.loadtxt(data_dict['frequencies'])
        else:
            # if this is not a string, assume it to be the data
            frequencies = frequency_data

        if frequencies.size != len(data_dict['crt']):
            raise Exception(
                'number of frequencies does not match the number of data files'
            )
        self._init_frequencies(frequencies)

        for frequency, filename in zip(frequencies, data_dict['crt']):
            subdata = np.atleast_2d(np.loadtxt(filename, skiprows=1))
            if subdata.size == 0:
                continue
            # extract configurations
            A = (subdata[:, 0] / 1e4).astype(int)
            B = (subdata[:, 0] % 1e4).astype(int)
            M = (subdata[:, 1] / 1e4).astype(int)
            N = (subdata[:, 1] % 1e4).astype(int)

            ABMN = np.vstack((A, B, M, N)).T

            magnitudes = subdata[:, 2]
            phases = subdata[:, 3]

            self.tds[frequency].configs.add_to_configs(ABMN)
            self.tds[frequency].register_measurements(magnitudes, phases)