OTDR Waveform Evaluation Tool Enabling Automatic Identification of Location and Cause of Faults

3.1 Overview of tool

An overview of the developed OTDR waveform evaluation tool is shown in Fig. 3. The tool is data analysis software that runs on a Windows personal computer and allows for easy identification of abnormal sections and abnormality types in OTDR waveforms. By inputting the OTDR measurement data (the Standard OTDR Record (SOR) data format extension file [2]), the tool automatically performs a batch waveform analysis on all the measurement data in the folder, identifies abnormal sections and abnormality types, and displays the results in a list format. The abnormality type that can be detected with this tool and examples of their OTDR waveforms are shown in Fig. 4. The tool can automatically determine five types of abnormality: cable loss abnormality (Fig. 4(a)), connection loss abnormality (Fig. 4(b)), reflection abnormality (Fig. 4(c)), dead-zone abnormality near the waveform edge (Fig. 4(d)), and measurement error (Fig. 4(e)). Even if multiple abnormalities are present on a single waveform, the tool can identify the abnormality type for each individual abnormal section, allowing for comprehensive identification of all abnormalities in the waveform. We describe the process of abnormality determination with this tool and its other functions.

Fig. 3. Overview of OTDR waveform evaluation tool.

Fig. 4. Examples of OTDR waveforms by abnormality type.

3.2 Process of determining abnormality type

The flowchart of the abnormality determination process using the tool is shown in Fig. 5. The tool incorporates an algorithm that automatically identifies connection points and cable sections in the OTDR waveform and analyzes them separately. For connection points, the loss and return loss are analyzed. Connection points where the loss exceeds the threshold are determined to have a connection loss abnormality, and connection points where the return loss is below the threshold are determined to have a reflection abnormality. For cable sections, the loss in each short section is analyzed. Sections where the loss (converted to loss per kilometer) exceeds the threshold are determined to have a cable loss abnormality. If the section is located at the start of the waveform and the waveform has an exponential shape, it is judged to be a drop in reflection caused by a connection failure between the cable and OTDR and determined to be a dead-zone abnormality near the waveform edge. If a cable section is not recognized, it is determined to be a measurement error. This abnormality determination process is designed to be carried out sequentially on all OTDR measurement data, enabling the tool to automatically determine abnormality type in a large number of OTDR waveforms.

Fig. 5. Flowchart of abnormality determination with OTDR waveform evaluation tool.

3.3 Other functions of the tool

In addition to the automatic analysis of waveforms, the OTDR waveform evaluation tool also supports manual analysis. An image of the operation interface for manual analysis is shown in Fig. 6. When any file in the list is clicked, the OTDR waveform of the selected data is displayed in the graph box and can be manually analyzed using the vertical and horizontal graph cursors. Waveforms can be viewed instantly without opening and closing files, and the position of the graph cursors automatically moves to the abnormal section. Therefore, manual analysis is made more efficient than before. The list of abnormality determination results can be searched by filtering according to conditions such as file name or abnormality type, and the results can be exported in CSV (comma-separated values) format. As described above, the tool supports many additional functions, enabling it to be used flexibly in a variety of scenarios.

Fig. 6. Operation interface of manual analysis function.