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Event types and its possible causes - DTX Compact OTDR Module

Event Type Definition Possible Cause
OTDR Port The tester’s OTDR port connector. The tester identifies the OTDR port connection and grades its quality, as shown on the OTDR details screens.
Reflection A pulse of light reflected back to the OTDR. Caused by a connector, tight bend, or crack in the fiber. Small reflective events may actually be ghosts.

If the reflection is not caused by a connector, inspect the cable for tight bends or damage. Use the VFL (Visual Fault Locator) to verify the fault.
Loss A point where the level of reflected light suddenly decreases. Caused by a splice or bend.

If the loss event is not caused by a splice, inspect the cable for tight bends. Use a VFL (Visual Fault Locator) to verify the fault.
Launch Event The end of the launch fiber.

The tester identifies these events if launch and receive fibers are connected and Launch Compensation is enabled in Setup.
Receive Event The beginning of the receive fiber.
Ghost Source A reflective event that is causing a ghost. Tip: On some traces with multiple ghosts, only the first ghost may be identified in the event table. You can usually determine that other reflections are ghosts because they occur at multiples of distances to connectors and they show almost no loss.

Caused by a dirty or unseated connector, highly-reflective connector, a connector with the wrong polish, a sharp bend, or a crack in a fiber.

Verify that the connector is seated properly. Inspect connectors that cause ghosts. If a connector does not seem to be the ghost source, use a visual fault locator to check for bends or cracks near the ghost source.

A ghost may have multiple sources. The tester identifies only one possible source. Look for reflective events with high loss or excessive tailing for other possible sources.
Ghost The event is a duplicate reflection caused by light bouncing back and forth between connectors. Caused by a dirty or unseated connector, highly-reflective connector, a connector with the wrong polish, a sharp bend, or a crack in a fiber.

Find the Ghost Source in the event table to determine where to look for the fault. The ghost source is always before the ghost. The event table does not show ghosts that occur after the end event.

If the ghost source is a hidden event, the tester may not identify a ghost event as a ghost.
Hidden The event is within the attenuation deadzone of the previous event. The event is detected, but not enough information is available to measure its loss separately from the previous event. Since the hidden event’s loss can’t be determined, it is not shown.

The hidden event may be a connection, a sharp bend, or a crack within the deadzone of the previous connection.

If the event is not a connection, inspect the fiber near the event's location. Use a visual fault locator to reveal faults.
Gainer An apparent gain in the strength of the returned signal Caused by a connection between two fibers with different backscatter coefficients, numerical apertures, core diameters, or mode field diameters.

A gainer can also occur when measuring loss across a very reflective connection.

Clean the connection. Check the fiber type on either side of the connection. Replace fiber if necessary. Matching fibers may have different tolerances, which can cause gainers at a connection. In these cases, the connection is good and does not require rework.

Tip: If the gainer is caused by different backscatter coefficients, and you test the fiber from the other end, the gainer event will show a loss. Adding this loss to the event’s gain provides the true loss of the event.
Weak Signal The signal is attenuated below the background noise level before the end event is reached. No fiber is attached to the OTDR port, the fiber is too short, or there is a bad connector or broken fiber somewhere near the tester. May also occur if the fiber has very high loss, or if the tester is in Manual OTDR mode and the Pulse Width is too narrow.

If the OTDR trace and event table show that the fiber is very short, check for bad connections and broken fibers within a few meters of the tester.
Out of Range The tester did not find an end event. This can occur in Manual mode when the selected range is too short.

In Auto mode, Out of Range can occur when the cabling is much longer than the module's range. Rarely, very bad connections along the cabling can cause the OTDR to select a range that is too short.

For Manual mode, select a higher range in Setup.

For Auto mode, compare the expected cabling length to the module's test range. If the length is within range, try testing in Manual mode with the maximum range setting.
No Fiber
No fiber is attached or the fiber is too short to measure. No fiber is attached to the OTDR port, the fiber is too short, or there is a bad connector or broken fiber somewhere near the tester.

Check for bad connections and broken fibers within a few meters of the tester.
No Signal There is a problem with the module.
If this continues to occur, contact Fluke Networks for assistance.
End The end of the cabling. The tester identifies the end of the cabling as the point where the backscatter stops. The tester does not measure the loss of End events. Note that a very high-loss event, such as a sharp bend, can appear to be the end of the cabling.
Hidden End The end of the cabling is hidden by a reflective event.

Learn About:
- OTDR

Author: Adrian Young

Creation Date: 2014-03-03

Last Modified: 2014-03-03

 
 
 
 
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