Tektronix TekRanger 2 TFS3031, Руководство по обслуживанию

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Performance Check – TekRanger 2 (serial nos. B052000 and above)
TFS3031 TekRanger/TekRanger 2 Service Manual
4–5
Loss dead zone is a measure of the distance around a reflective event where fiber
backscatter measurements are not valid. A typical reflective event creates a
signal that is several orders of magnitude larger than the backscatter signal. After
the signal from the reflective event ends, the OTDR requires some time for the
displayed waveform to return to the backscatter level and allow accurate fiber
backscatter measurements. The loss dead zone is measured from the point where
the waveform deviates from the backscatter by 0.5 dB at the start of a -40-dB
event to the point where the waveform recovers to within 0.5 dB of backscatter
following the event.
Dead Zone (refl)
0.5 dB
0.5 dB
Reflectance is the ratio of the reflected power, P
r
, to the incident power, P
i
, at
any specific point or event on an optical fiber. In dB, reflectance is the 10 log of
the ratio of the reflected power divided by the incident power. The reflectance
accuracy of the TFS3031 is measured against a traceable backreflection standard
(JDS Fitel BR1). The backreflector is set to a known backreflection level of -40
dB and the TFS3031 measures the reflection. The measurement must be within 4
dB of the actual value.
Tektronix has developed a unique process to allow the event loss and distance
accuracy of the TFS3031 singlemode options to be traceable to NIST (National
Institute of Standards and Technology). For the first time in an OTDR, this
provides a check of the instrument’s ability to measure accurately the distance to
an event and the loss of that event. The process uses precisely characterized
fibers with events with calibrated losses at calibrated locations on the fibers.
Attenuation Dead Zone
Reflectance
Event Loss and Distance
Accuracy