YOKOGAWA AQ7260 OTDR, User Manual, Page: 436 / 442

Chapter 10 APPENDIX
10-9
Connection point
Points at which the optical fiber is fused (including mechanical connection) or points where
connectors are connected by adapter.
Dead zone
Areas that cannot be measured due to influences by Fresnel reflection. There are two
dead zone types as shown below. For details, refer to the explanation given for each type.
•
Event dead zone
•
Attenuation dead zone
Distance measuring accuracy
OTDR measures the time the emitted pulse ray takes to return, and calculates the
distance (L) using the following formula.
L
=
C
×
T/(2N) [m]
C: Speed of light traveling in the vacuum
T: Time spent before the pulsed ray is returned (received) after it is emitted
N: Group index
The reason why the distance is divided by “2” is to measure the time taken by the pulse
ray to travel back and forth through the optical fiber.
Thus, measured distance is not accurate unless the given group index is accurate.
Distance range
Range of distance the instrument can display. Select a range that is longer than the optical
fiber to be measured. However, the larger the distance range, the longer the measurement
time.