Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 72)

Operator’s Manual
70
WE-OM-E Rev A
TDR Mode
TDR mode is selected by touching the TDR button in the "Horizontal" menu or by pressing the TDR
button on the instrument front panel in the Quick Set control group. This displays the TDR menu tab
that appears with the "Horizontal" menu. The acquisition mode is set to Sequential and waveform
averaging is enabled (32 sweeps). The "TDR Main" menu provides access to control of the TDR
step generators in the ST-20 sampling modules. Only channels that contain ST-20 modules are
capable of generating a TDR step. Channels containing other modules or no module will be
indicated in the menu with the designation: “Pod has no TDR capabilities” or “Pod is missing.”
V (volts) Displays the sum of the incident and reflected voltages at the sampling diode
within the sampling head.
ρ (reflectance) The vertical scale is the reflection coefficient: V
reflected
/V
incident
. varies from 0 (a
perfectly matched load with no reflection) to 1 (an open circuit with 100%
reflection).
Ω (impedance) The vertical scale is the characteristic impedance of the network connected to
the TDR head. The impedance is determined from the reflectance using the
relationship
( )
( )
ρ
ρ
−
+
=
1
1
0
Z Z
jX (reactance) The display is scaled in volts and parameter P1 indicates the reactance
(capacitive or inductive) of the section of the trace between the cursors. The
cursors are turned on automatically when jX is selected. The reactance is
determined by integrating the voltage between the cursors. A negative area
results from the capacitive reactance and a positive area from an inductive one.
The reactance is computed from