Fluke DSP-2000 - Manual (Page 128)

DSP-100/2000
Users Manual
7-16
Reflections from Opens
An open, or break, in the cable represents an abrupt increase in the cable’s
impedance. The impedance of an open is nearly infinite. In an open cable, a
signal’s energy is not dissipated by a terminating impedance, so the signal
bounces back towards the source. This reflection appears at the source with the
same amplitude and polarity as the original signal, as shown on the next page in
Figure 7-9. By measuring the amount of time taken for the reflected pulse to
return, the test tool can determine the location of the open in the cable.
Transmitted Pulse
Reflected Pulse
End of Fault
Open
Cable
Transmitted Pulse
Reflected Pulse
Short
Transmitted Pulse
No Reflected Pulse
Terminator
(Matches cable
characteristic
impedance)
ENTER
TEST EXIT
SAVE
1
2
34
OFF
PRINT
MONITOR
SETUP
SPECIAL FUNCTIONS
SINGLE TEST
AUTO TEST FAULT INFO
DSP-2000
CABLE ANAL
YZER
ENTER
TEST EXIT
SAVE
1
2
34
OFF
PRINT
MONITOR
SETUP
SPECIAL FUNCTIONS
SINGLE TEST
AUTO TEST FAULT INFO
DSP-2000
CABLE ANAL
YZER
ENTER
TEST EXIT
SAVE
1
2
34
OFF
PRINT
MONITOR
SETUP
SPECIAL FUNCTIONS SMART REMOTE
SMART REMOTE
SMART REMOTE
SINGLE TEST
AUTO TEST FAULT INFO
DSP-2000
CABLE ANAL
YZER
gc35f.eps
Figure 7-9. Signals Reflected from an Open, Shorted, and Terminated Cable