def gen_data_sheet(self, datafile, para_meter, scale=1.75, steady_time=300):
        """
        datafile, sheetname, x_axis_name, y_axis_name, title,
        Function:
            Turn realtime bw data into picture, and save into specific sheet
        Input:
            sheetname: If already exists, new chart will be added continuely.
                       Otherwise, it would create new sheet;
            x_axis_name: x_axis name;
            y_axis_name: y_axis name;
            title: picure name;
            scale； size of picture.
        """
        filename = os.path.splitext(os.path.split(datafile)[1])[0][:-5]
        para_meter['filename'] = filename
        source_data = np.loadtxt(datafile, dtype=int, delimiter=',')[:, :3]
        is_bw = 'bw'in para_meter['title'].lower()
        file_data = process_rt_data(source_data, is_bw)
        pic_path = generate_rt_pic(file_data, para_meter, scale)
        pic_path_steady = generate_steady_rt_pic(file_data, para_meter, scale, steady_time)
        if para_meter['sheetname'] in self.sheetname_dict.keys():
            self.sheetname_dict[para_meter['sheetname']] = \
                self.sheetname_dict[para_meter['sheetname']] + 1
            chart_sheet = self.workbook.get_worksheet_by_name(para_meter['sheetname'])
        else:
            self.sheetname_dict[para_meter['sheetname']] = 1
            chart_sheet = self.workbook.add_worksheet(para_meter['sheetname'])
        chart_sheet.insert_image('B%d' %
                                 (5 + (self.sheetname_dict[para_meter['sheetname']] - 1) * 30),
                                 pic_path)
        chart_sheet.insert_image('Q%d' %
                                 (5 + (self.sheetname_dict[para_meter['sheetname']] - 1) * 30),
                                 pic_path_steady)
        self.__insert_value(chart_sheet, file_data,
                            5 + (self.sheetname_dict[para_meter['sheetname']] - 1) * 30,
                            steady_time)
        self.pic_list.append(pic_path)
        self.pic_list.append(pic_path_steady)
datafile, sheetname, x_axis_name, y_axis_name, title,
        Function:
            Turn realtime bw data into picture, and save into specific sheet
        Input:
            sheetname: If already exists, new chart will be added continuely.
                       Otherwise, it would create new sheet;
            x_axis_name: x_axis name;
            y_axis_name: y_axis name;
            title: picure name;
            scale； size of picture.