IBM 5500 Operational, Installation, And Maintenance Manual page 110

110
Chapter 6: Twinax Client Cabling Requirements and Problem Solving
- Frequency response: 10 KHz to 100 MHz
- 50 ohm coax connector (or adapter to 50 ohm coax connector)
- Sensitivity at rated load: 0.17 microamp with 1 millivolt sensitivity and
6 ohm transfer impedance. If a current probe is available with a different
sensitivity, an adjustment will have to be made. For example, for 1
microamp with a 1 millivolt sensitivity, the oscilloscope trace will be
1/5 as large or the volts/div will have to be set to 2 millivolts to get the
same size of oscilloscope trace.
• One coax cable.
Step 2. Set the oscilloscope switches as follows:
CH 1 VOLTS/DIV: 10 millivolts
AC-GND-DC: DC
INVERT: Out (not inverted)
VERT MODE: CH 1
A and B TIME/DIV and DELAY Time: Set A to 10 milliseconds, (no delay
is used).
HORIZ DISPLAY: A lock knob
TRIG MODE: AUTO
COUPLING: DC
SOURCE: CH 1
SLOPE: plus
Step 3. Clamp the current probe around each twinax cable off of the
twinax attachment box.
Adjust the trigger level until you see a trace on the oscilloscope similar to one
of the traces shown in the diagrams shown on page 111 and page 112.
Step 4. Record the peak to peak level for each of the cables measured.
(For example, Port 0: 30 mv, port 2: 10 mv,... Port 7: 10 mv). All
measurements should have approximately the same value if all twinax cables
have the shields connected. If a measurement is higher than the others (such
as 30 mv versus 10 mv), the cable has an open shield. Use the port tester or an
ohm meter to find the open shield.
Notes:
1. A "good" level varies from system to system. 10 mv might be good while
30 mv indicates an open shield. At a different account, 40 mv might be
good while 80 mv is bad. The relative levels are important with the higher
signal indicating the cable with an open shield.
2. Heavy horizontal line in the oscilloscope diagrams represents background
noise.
Figure 40 shows a good shield, WSC only polling (system running, but no one
is signed on to a display station on this WSC).
Planning, Installation, and Maintenance Guide