def _get_float(txt):
    """
    returns the floating point number from string
    
    Parameters
    ----------
    txt  : string
           string of the number
             
    Returns
    -------
    return : float or None-type
             number from txt
             None if conversion is not possible
    """
    try:
        return float(txt.replace(',', '.'))
    except:
        return None
