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TDR System
TDR System - Continued

Calibration Procedure For Digitizing Oscilloscope Hewlett Packard, Model 54121T, Model 54120B, And Model 54121A Page Navigation
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TB 9-4931-538-40
NOTE
If there is a rising edge on display, the TDR step adjustment
must  be  performed  before  continuing  this  procedure
(SECTION IV, paragraph 24 below).
NOTE
Use four terminal ohm measurement technique for (4) and (5)
below.
(4) Using necessary adapters, connect 50  termination to multimeter. Record dc
resistance ______________.
(5) Remove 50  termination and connect APC 3.5 short as in (4) above. Record dc
resistance ______________.
(6) Subtract the resistance (short) (5) above from the termination (4) above. Step (4)
______________ - Step (5) ______________ = ZL ______________.
(7) Solve for ER using this formula: ER = 200 ((ZL - 50) (ZL + 50)). Round to
nearest 0.01 mV. (ER can be a negative number). ER = _____________mV.
(8) Connect 50  termination to Channel 1.
(9) Press More and Delta V keys. Press TDR V Markers key until On is highlighted.
(10) Press Preset Levels key until 50-50% is highlighted and press Auto Level Set
key. V(1) will read 0 V 2mV. Record the value of V(1) = _______________mV.
(11) Press Timebase key and set TIME/DIV to Sweep Speed = 1.00 ns/div.
(12) Press Channels and VOLTS/DIV keys and set Sensitivity = 80.00 mV/div
and OFFSET to Offset = 200.0 mV.
(13) Press Delta V key and ensure that Preset Levels is still at 50-50%. Press
Auto Level Set key.
(14) Press Delta t key and press TDR T Markers key until On is highlighted.
Press START ON EDGE key until POS 1 is highlighted and STOP ON EDGE key until
POS 1 is highlighted. Press Precise Edge Find key.
(15) Record start position value (_____________ns).
(16) Press STOP MARKER key and set Stop Position = the value of the START
MARKER +1 ns.
(17) Press Timebase key and set TIME/DIV to Sweep Speed = 100 ns/div,
DELAY to Delay = the value of the STOP MARKER.
(18) Press Channels and VOLTS/DIV keys and set Sensitivity = 2.000 mV/div.
(19) Press Delta V and MARKER1 POSITION keys and overlay the trace at the
right edge of display. Record V(1) value from display V(1) = ________________ mV.
(20) Subtract the value of ER (7) above from the value recorded in (19) above. This
value will be between 198 and 202 mV. Record this value _______________mV.
20
Change 1


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