Omron CS1W-CLK12-V1, Руководство по эксплуатации

Страница: 302 / 312

285
Handling and Using GI Cable Appendix D
Note When optical fibers are joined by a fused connection or connector connection, the loss between nodes
must be within the limits shown in the following table.
Measuring Light Loss
Measure the transmission loss when the Optical Fiber Cable is installed and during periodic inspections to
determine whether an optical fiber has broken, disconnected, or deteriorated.
Cutback Method
The CCITT (International Telegraph and Telephone Consultative Committee) and IEC (International Electro-
technical Commission) have adopted the cutback method as the standard technique for measuring transmis-
sion loss.
Theory
Connect the dummy fiber to the fiber that is being measured and measure the light power (P
1
) at point B. Next,
disconnect the
l
km of fiber at point A and measure the light power (P
0
) at point A. The loss in the measured
fiber is simply the difference between these two measurements.
Points A and B are often separated by some distance, so 2 calibrated power meters are actually required to
measure the light power at the two points.
Simple Measurement with a Light Tester
A light tester can be used to take a simple loss measurement, as shown in the following diagram.
First, the light tester is self-calibrated by connecting a short fiber cord between the transmitter and receiver.
Next, the fiber to be measured is connected to calculate the difference between the transmitted light power
(P
1
dBm) and the received light power (P
0
dBm).
Fiber loss: L = P
1
– P
0
dB
When a two-core cable is being used, a Connector Adapter can be connected to the far end of the cable and
the round-trip transmission loss through the entire cable can be measured with a single light tester.
Cable Allowable loss
50/125
µ
m 3 dB/km
62.5/125
µ
m 3.5 dB/km
Dummy fiber for
loss measurement
Optical Fiber Cable
Connection
Light source
2 m
α
=
l
P
0
−
P
1
[dB/km]
Light tester
Measured
fiber
Receiver
Transmitter
Light tester
Receiver
Transmitter
Light tester
Receiver
Transmitter
Measured
fiber
Connector Adapter