IBM 5500 Operational, Installation, And Maintenance Manual page 120

120
Chapter 6: Twinax Client Cabling Requirements and Problem Solving
• Look for a bad reflection. The B setting of 0.1 msec displays cables of up
to 100 m (328 ft) or the first part of longer cables. To display longer
cables of up to 1524 m (5000 ft), use the B setting of up to 2 msec.
- The 0.1-msec setting equals 9.9 m (32.47 ft)/div for a solid poly cable
- The 2-msec setting equals 198 m (649.4 ft)/div for a solid poly cable
• To magnify small changes, adjust the Channel 1 position knob and
Channel 1 volts/div to a lower setting.
• Major faults at long distances can cause reflections no larger than smaller
faults close to the test end of the cable.
• After finding mismatches, you can measure close to the fault to describe it
more accurately.
• Faults too close to the tested end of the cable, within 6 m (20 ft), cause
reflections to occur within the rise time of the oscilloscope. Test from
both ends of the cable if no clear reflection of the fault is displayed.
Note: The 6-m (20-ft) measurement is approximate and depends on the
oscilloscope that you use.
Oscilloscope Display Examples:
See Figure 51 through Figure 57.
Figure 51 shows a good cable that is 155.5 m (510 ft) long. A gradual upward
slope of the displayed signal is normal after the first division and appears as a
higher upward slope as the B-sweep time increases.
0.5 V
A=20 µs
B=0.2 µs
Figure 51: Normal Cable (Properly Terminated)
Figure 52 shows a cable that is shorted at the end to show downward
reflection and length.
Length of sweep = 7.8 div
B setting = 0.2 µs/div
Planning, Installation, and Maintenance Guide
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