Analyzing OTDR traces on a PC with a Windows user interface - optical time domain reflectometer - Technical

Hewlett-Packard Journal, Feb, 1993 by Wilfried Pless

One of the tasks that is important to OTDR users is the ability to save measurement results on suitable media and to compare results from different measurement sessions. With this capability, users can obtain information about the aging of fibers, obsenze the effects of bending fibers very early, and do all the statistics that are relevant for evaluating the quality of the transmission link.

Besides offering printers for documenting and saving measurement results, there needs to be software that allows the user of an OTDR to do analysis and documentation tasks on a remote computer such as a PC.

The HP 81460SA IPC_OTDR)is a software package that enables users to communicate with the HP 8146A from a PC. This software offers the means to display OTDR measurement results, measure characteristic values like positions and losses, measure attenuation between events, perform Scantrace for finding and characterizing events, add comments to trace data, and do extensive compares for up to eight traces. All this software runs in the Microsoft[R]-Windows environment, which almost guarantees easy-to-use operation.

Fig.1 shows the software's main window and some of its child windows (Trace, Overview, and Marker). As the CUA standard suggests,* the PC_OTDR software has as its leftmost menu item the File menu which provides menus items for reading a trace from the disk, saving it, printing it, and exiting the program. Another menu item suggested by the CUA standard is the Help menu on the rightmost side of the main window. The help facility offers all the information necessary to operate the PC_OTDR software without a manual.

The menu items View, Analysis, and Events are PC_OTDR-specific menus. Within the View menu the user can select the child windows to be displayed, and set preferences such as trace colors and distance units. The Analysis menu offers the analysis mode, which displays the result in the Marker window. In the Analysis menu, the user can choose to display either the 2-point 1ess between markers A and B or the 2-point attenuation (or the least-squares approximation attenuation) between A and B. The Analysis menu can also be used to select the splice mode for positioning auxiliary markers to determine splice loss values and the return 1ess mode for evaluating the quality of connections.

* The IBM Common User Access lCUA) standard describes how Windows applications should look to make them consistent and easy to use.

The Events menu allows the user to scan a trace for events and its characteristic values, jump between events, add additional events, and delete events from the list.

The child window Trace provides a zoomed-in or zoomed-out display of the traces from a measurement. Fig1 shows as an example four traces of the same fiber, collected at different times. The top trace shows a measurement that was made directly after the installation of the fiber. Because of bending loss somewhere in the fiber, at about 3 km the power from the fiber became weaker over time resulting in the noisy bottom trace making it difficult to find the splice at marker A. By comparing up to eight traces the user can easily see how the fiber performs over the years. Another useful comparison is to compare traces that were measured with different pulse widths (e.g., 5 ns versus 100 ns) to see the influence of pulse width on resolution.

The Overview window shows where the zoomed-in portion of the current trace shown in the Trace window is located relative to the whole fiber.

The Marker window mentioned above lists the positions of markers A and B, the distance between them, and the result of the analysis mode that was chosen in the Analysis menu.

As with the OTDR, the user can run Scantrace with the PC_OTDR software. The result of such a scan is shown in Fig. 2. The Event Table window lists the types of events and their associated values. With just one mouse click on a single event the user can jump directly into an event to look at details in the Trace window.

Other window features like informative dialog boxes allow the user to easily select traces to be displayed or enter comments and trace information when saving a trace on a disk.

Wilfried Pless

Project Manager

Boblingen Instrument Division

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