QUIZ BY JIM HAYES
1. Measurement accuracy depends on ________.
A. How closely a measurement agrees to the real value
B. The number of figures in the measurement
C. When the instrument was last calibrated
D. How much an instrument costs
2. Which of the following optical time-domain reflectometer
(OTDR) length measurements is more accurate?
10. 3 kilometers (km)
10. 33 km
D. None of the above
3. If you measure the loss of a fiber optic cable several times
and get values of 2. 31 decibels (dB), 2. 35 dB, 2. 20 dB and
2. 27 dB, you are seeing ________ errors.
4. If you calibrate your light source and power meter to “0 dB”
before measuring the loss of several fibers in a cable, but it
drifts to 0.2 dB before you take the measurements, you are
introducing a(n) ________ error.
5. If your company has three optical power meters and you
check them with the same source at the same optical power
level and get different values, the differences are probably
due to ________ errors.
6. When measuring loss of multimode fiber cable plants,
it is important to consider ________ to get accurate
A. Test source wavelength
B. Test source modal distribution power output
C. The quality and condition of reference test cables
D. All of the above
7. An error in length measurement with an OTDR will not
affect the measurement of the attenuation coefficient of a
fiber in decibels per kilometer.
8. The concern over loss errors caused by modal distribution
in multimode fiber has led to the development of ________
to specify source mode distribution.
A. Encircled flux
B. Coupled power ratio
C. Mode power distribution
D. All of the above
9. If we are careful in setting up a fiber optic loss
measurement of a short cable plant with a loss budget
of 2.00 dB, our measurement uncertainty is likely to be
A. Less than 0.02
B. ± 0.02–0.05
C. ± 0.20–0.30
D. ± 0. 50–1.00
10. Whether you use one, two or three reference cables
when setting the “0 dB” reference for a loss test with a
light source and power meter does not affect the accuracy
of the measurement.
HA YES is a VDV writer and educator and the president of the Fiber Optic Association. Find him at
Fiber Optic Testing Accuracy
Installation techs use instruments to make measurements to verify their work and sometimes find
measurements that do not agree. Let’s test your knowledge of fiber optic measurement accuracy.
(See my fiber optics column on page 132 for more.) ANSWERS ARE ON PAGE 143. TO TAKE THE QUIZ