VDV Works Virtual Hands-On Training
Fiber Optics Testing: Using OTDRs
 
Part of the VDV Academy Fiber Optic Training Programs

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Read About OTDRs

 Dos & Don'ts

 Tools

 Setup

Take Data

Viewing the trace

Measure Loss

Modify Test Parameters

Compare Traces

Troubleshooting

Quiz

More Useful References

 Understanding OTDRs

"Virtual Hands-On" Termination

"Virtual Hands-On" Testing


Viewing the Trace

Just like in other Windows programs, you can maximize the windows for best viewing and switch between traces using the WINDOW command on the toolbar.


Click on the 'Hide trace' button to move it to the bottom of the computer screen.
Double click on the minimized trace at the bottom of the screen to return it to view.
Click on the 'Maximize trace' button to make the picture fill up the entire screen and enlarge the viewing area.
Click on the 'close trace' button to return the picture to the original storage location.



There are several important features in the "Information Panel" window that will help analyze the data that's collected.

        

On the left side of the trace window is a list of details specific to the trace that's being displayed (see image to the right). The details will change depending on which measurement tool is active and where the operator has located the measurement markers.

Markers are the vertical lines that can be inserted to mark or select a segment of the cable for a closer analysis. Every trace can display two markers at one time.

Use the markers to measure the distance or the difference in distance and loss between two markers. Markers will show the distance to the end of the fiber or to an event - a splice, connector, location of a break or stress loss.

panel

L1, km reveals the position of markers #1(.9674 km). Marker #1 is always red on a colored monitor and it appears on the left side of the screen. The left marker can be positioned by either using the left or up arrow key or left mouse button.

L2, km reveals the position of marker #2. Marker # 2 is always blue on a colored monitor and it is the right cursor on the screen. It can be moved using the right or down arrow key or the right mouse button. On this trace the left marker is located at 1.0 km.

dL, km is the distance between the two markers, used for instance for measuring distance or the length of a fiber for measuring attenuation coefficient.

dB is the difference in dB level (loss) between the points on the trace where it crosses the markers.

dB/km is the dB difference divided by the length which is the attenuation coefficient, relevant for single fiber lengths only.

Traces shows the trace files currently open and the window at the bottom shows the entire trace.







Inserting the markers:

Mouse Method:
Roll the mouse to the part of the trace that the left marker should appear at.
Click the left mouse button to place the left marker at the mouse location.

Roll the mouse to the place that the right marker should appear at. Click the right mouse button to place the right marker in a mouse location.

To move a marker with the mouse: position the mouse on the cursor so the mouse arrow appears as a double headed arrow. Click and drag the marker to the proper location.

Keyboard/Arrow method:
Left Marker:
Press the up arrow key to move the left marker to the right
Press the left arrow key to move the left marker to the left

Right Marker:
Press the down arrow key to move the right marker to the left.
Press the right arrow key to move the marker to the right.

Measurement Parameters

The bottom of the screen reminds the user of the parameters that were set and the scale of vertical and horizontal losses that the grid divides.
You can use these grid lines to estimate distance and loss.

Another important feature in the window is the grid system of lines that appear behind the trace. The vertical lines divide the length of the cable while the horizontal lines represent levels in the signal.

The Trace

The trace that appears below can tell a lot about the cable it tested. From the trace, the fiber is 5.5 km long. The cable has four events that can be counted from left to right as peaks or small bumps in the line.

The first peak shows where the launch cable connects to the OTDR.

The second peak is the connector (#1) on the end of the launch cable with some reflectance.

The third peak is a connector (#2) with some reflectance.

The fourth peak (near the middle of the trace) is a splice. It appears to be a mechanical splice because there is some reflectance.

Ther end of the cable is where the trace becomes only noise.

 You can zoom in on a spceific part of the trace using the ZOOM tools. Use the scroll bars on the bottom and right of the window to move around the trace in the Zoom mode.

The small window on the left side of the screen is the relative locator. It will show which portion of the trace is being displayed. 

The last five buttons on the far right of the tool bar can be used to zoom in or out of the trace for close up views.
The button on the far right will restore the trace to its original view size.
 

The buttons on the toolbar allow changing the dimensions on the distance and dB scales so you can ZOOM in or out on a portion of the trace.

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