Data Sheet

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Distance calculation formula of OTDR: Distance = (c/n) × (t/2)
Among which: c= speed of light in vacuum (2.998 x 108 m/s)
t = Time delay between transmitted pulse and received pulse
n = refractivity of optical fiber during testing process (nominated by manufacturer)
When displaying the whole trace, each point on the trace graph represents the average
value of several sampling points. The value of each sampling point can be found by reducing or
magnifying the trace.
Fig. 6-1. OTDR Principle Diagram
6.3 Instruction of Events Categories
Events on optical fiber indicate these abnormal points that brought loss or sudden change
of reflection power beyond normal scattering of optical fiber material, including various kinds of
connection and bending, loss of flaw or fracture on the optical fiber link.
Event points displayed on the screen is the abnormal points in the optical fiber that led to
deviation of trace, which are classified with special symbols on the trace.
Events include “reflection event” and “non-reflection event”.
6.3.1 Initial Event
“Initial event” on the OTDR trace is the event that marks the starting point of optical fiber.
Under default conditions, “initial event” is located at the first event (usually be the first
connector of OTDR) of the tested optical fiber. The event belongs to reflection event.
6.3.2 End Event
“End event” on the OTDR trace is the event that marks the terminal of optical fiber. Under
default conditions, “end event” is located at the last event of the tested optical fiber. The event
is called optical fiber terminal event (usually be the end or fracture point of the tested optical
fiber), which usually belongs to reflection event.
6.3.3 Reflection Event
When optical pulse energy is reflected (such as on the connector), reflection event occurs.
On the trace, reflection event is shown as peak signal, as shown in Fig.6-2.