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(2)
(3)
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747-400 MAINTENANCE MANUAL
(b)
VERT SCALE - sets the vertical sensitivity (millirho per division) or vertical gain (dB).
(c)
DIST/DIV - sets the number of feet (meters) for each division across the LCD.
(d)
Vp - velocity of propagation. You set these controls to the propagation velocity value of the cable.
(e)
POWER - pull for power on, push for power off.
(f)
.POSITION - moves the waveform up or down on the LCD.
(g)
<>POSITION - moves the vertical cursor across the LCD. The waveform is also moved when the cursor gets to the far right or left side of the LCD.
(h)
MENU - gives access to the menu.
(i)
VIEW INPUT - permits you to view or remove the waveform shown on the LCD.
(j)
VIEW STORE - shows the waveform that is kept in memory.
(k)
VIEW DIFF - shows the result of the waveform shown minus the waveform in memory.
(l)
STORE - puts the waveform into memory.
Vp is the speed of a signal down the cable. This value is different
for different types of cables. If you do not know the Vp, refer to
Table 1 for approximate values.
NOTE: If the Vp is set incorrectly, the failure will show
____ but the distance will possibly not be accurate.
~.................................................. | TYPE OF CABLE | PROBABLE Vp | .................................................... .................................................... | Jelly Filled | .64 | .................................................... | Polyethylene (PIC, PE, or SPE) | .66 | .................................................... | PTFE (Teflon) or TFE | .70 | .................................................... | Pulp Insulation | .72 | .................................................... | Foam or Cellular PE (FPE) | .78 | .................................................... | Semi.solid PE (SSPE) | .84 | .................................................... | Air (Helical spacers) | .98 | 2..................................…...............1
TABLE 1
Bleed a cable before you attach it to the TDR to remove static from the cable. You can use a 50 ohm terminator and a BNC adapter to bleed a cable.
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747-400
MAINTENANCE MANUAL
(4)
You will always see a rising pulse at the start of the waveform. This is the test pulse from the TDR.
(5)
During this procedure the cable that you do a check of will be referred to as the applicable cable.
B. References
(1)
Wiring Diagram Manual
(2)
AMM 20-11-22/401, Rack-Mounted Electrical/Electronic Module
C. Special Tools and Equipment
(1) Tektronix 1502B - Time Domain Reflectometer
D. Access
(1) Location Zone
117/118 Electrical and Electronics Compartment
E. Procedure
S 862-002
(1) Prepare the applicable cable and the TDR (Fig. 201):
(a)
Pull the POWER button to the ON position.
(b)
Connect an adapter cable to the BNC on the front panel of the TDR.
(c)
Remove the black box at one end of the applicable cable (AMM 20-11-22/401).
(d)
Disconnect the applicable cable at the other end.
CAUTION:_______DO NOT DIRECTLY TOUCH THE RACK CONNECTORS. THIS CAN CAUSE DAMAGE. USE A BREAKOUT BOX. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747-400 AMM 飞机维护手册 STANDARD PRACTICES - AIRFRAME(84)
