Tektronix 1502C Manual De Usuario
Operator Tutorial
2–26
1502C MTDR User Manual
15. To exit Single Sweep, access the Acquisition Control Menu again, toggle the
Single Sweep is: line back to Off, then push the MENU button repeatedly
until the instrument returns to normal operations.
until the instrument returns to normal operations.
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).
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).
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.
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.
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 the reflection?
far away is the point on the cable that caused the 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 1502C does all this automatically and
displays the information on the LCD.
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 1502C does all this automatically and
displays the information on the LCD.