Operator Tutorial
1503C MTDR User Manual
2–23
TDR Questions and Answers
Q1:
What does TDR stand for?
A1:
Time-Domain Reflectometer.
Q2:
What is the difference between time domain and frequency domain?
A2:
Within the time domain, things are expressed in units of time (e.g.,
nanoseconds). In frequency domain, things are expressed in frequency,
cycles per second (e.g., kiloHertz).
Q3:
What does a TDR actually measure?
A3:
Voltage over time.
Q4:
How does a TDR display this information?
A4:
Voltage on the vertical axis (as amplitude of the waveform) and time on the
horizontal axis (as distance to the event).
Q5:
Does electricity travel the same speed (velocity) in all materials?
A5:
No. Electricity is like light; its velocity is affected by the material through
which it passes.
Q6:
What is that difference called?
A6:
The relative velocity of propagation (Vp). The velocity of the cable is
expressed in time/distance (e.g., feet per nanosecond). The velocity of
electricity traveling in a vacuum is compared to the velocity of electricity
traveling in a cable. This relationship is shown as a decimal number. A
relative propagation velocity of .50 would mean the electricity will travel at
50%, or one-half, as fast as it would in a vacuum.
Q7:
If a reflection takes 30 nanoseconds to return in a cable with a Vp of .66, how
far away is the point on the cable that caused thee reflection?
A7:
The one-way time would be 30 divided by 2, or 15 nanoseconds. The velocity
of 1 ns/ft in a vacuum would mean a distance of 15 feet. Because the cable
is slower, we multiply the distance by the Vp (.66 in this case) and arrive at
a distance of 10 feet. Of course, the 1503C does all this automatically and
displays the information on the LCD.
Q8:
What is resistance?
A8:
Resistance is the opposition to DC current flow, or DC voltage divided by DC
current.
Summary of Contents for 1503C
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Page 92: ...Appendix A Specifications A 6 1503C MTDR User Manual...
Page 104: ...Appendis B Operator Performance Checks B 12 1503C MTDR User Manual...
Page 122: ...Glossary Glossary 6 1503C MTDR User Manual...
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