User Manual

2-11
IM 735020-01E
Measurement Overview
Index
App
21
20
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14
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10
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4
3
2
1
2.4 Distance Measurement
Accuracy
The AQ7270/AQ7275 calculates the distance (L) by measuring the time until the
transmitted light pulse returns and using the equation indicated below.
L = C×T/(2N) [m]
C:
The speed of light travelling through a vacuum.
T:
The time from when the pulse is transmitted until the light returns.
N: Group refraction index
The reason why the equation divides by 2 is because the round-trip time of the optical
pulse is measured.
An error will occur in the distance measurement unless an accurate group refraction
index is specified.
Group Refraction Index Settings
The following group refraction indexes are assigned according to the wavelength on the
AQ7270/AQ7275.
850 nm: 1.46000
1300 nm: 1.46000
1310 nm:
1.46000
1490 nm: 1.46000
1550 nm:
1.46000
1625 nm: 1.46000
1650 nm: 1.46000
The selectable range is 1.30000 to 1.79999.
For the accurate group refraction index, check with the manufacturer of the optical fiber
cable.
Optical Fiber Cable Length and Distance Range
Select a distance range that is longer than the optical fiber cable you want to measure. If
the distance range is longer, the measurement time also increases accordingly.
Cable Length Distance Range
Unknown Auto
0 to 400 m 500 m
400 m to 800 m 1 km
800 m to 1.6 km 2 km
1.6 km to 4 km 5 km
4 km to 8 km 10 km
8 km to 16 km 20 km
16 km to 40 km 50 km
40 km to 80 km 100 km
80 km to 160 km 200 km
160 km to 240 km 300 km