IPC-TM-650 EN 2022 试验方法.pdf - 第610页
4.4 Fixture of plexiglass or other nonmetallic material. Cable hangers to suspend the cable in air (see Figure 2) 5 Procedure 5.1 Allow a minimum of one hour for TDR warmup and cali- brate the instrument per manufacturer…
1
Scope
This
method describes the test procedures
required to measure propagation delay in flat cables. Propa-
gation delay is defined as the time required for a pulse to
traverse a unit length of cable. Excessive propagation delay
will result in the malfunction of critical circuits due to the late
arrival of pulses. Propagation delay is directly proportional to
the effective dielectric constant of the insulation.
2
Applicable Documents
None
3
Test Specimen
3.1
One
pre-production or production sample1mto3m
long. The number of test samples should be determined by
the manufacturer and/or user.
4
Apparatus
4.1
In this test, propagation delay is measured using time
domain reflectometry (TDR). Commercial TDRs are readily
available and consist of a pulse generator and sampling oscil-
loscopes. The TDR to be used should be a Hewlett-Packard
1415A, Hewlett-Packard 1815A, Tektronix 1 S2 or equal.
4.2 Two
standard cable connection devices to terminate
each end of the test cable, which should match Figure 1. It is
made from a General Radio cable connector type 874-C62A.
4.3
A
509 load, type GR874 or equivalent, to terminate the
output of the TDR
IPC-2-5-18-3
Figure
1 Cable Connection Device
The
Institute for Interconnecting and Packaging Electronic Circuits
2215 Sanders Road • Northbrook, IL 60062
IPC-TM-650
TEST
METHODS MANUAL
Number
2.5.19
Subject
Propagation
Delay of Flat Cables Using Time
Domain Reflectometer
Date
7/84
Revision
A
Originating Task Group
Material
in this Test Methods Manual was voluntarily established by Technical Committees of the IPC. This material is advisory only
and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this
material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.
Equipment referenced is for the convenience of the user and does not imply endorsement by the IPC.
P
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4.4
Fixture
of plexiglass or other nonmetallic material. Cable
hangers to suspend the cable in air (see Figure 2)
5
Procedure
5.1
Allow
a minimum of one hour for TDR warmup and cali-
brate the instrument per manufacturer’s instructions.
5.2
Prepare
the test specimen by stripping approximately 13
mm of insulation from both ends of the cable. Separate the
ground and signal conductors and solder a copper buss
across the grounds of each end (see Figure 3). Solder a stan-
dard cable connection device to each end of the cable (see
Figure 4).
5.3
Adjust
the TDR settings as follows: Vertical-0.2 p/cm;
Distanceltime-20 ns/cm; Magnifier-10X. (For equipment other
than Hewlett-Packard, use settings as close as possible to
these.)
5.4
Terminate
TDR output using the 509 load.
5.5
Adjust
the magnitude delay dial so the 50Ω termination
is visible and positioned to the left on the screen. Adjust the
vertical position so the pulse trace leading edge crosses the
horizontal graticule center line at 10% of pulse height (see
Figure 5). Mark the position of the leading edge of the pulse
on the horizontal graticule (mentally or by camera). If a cam-
era is used, don’t advance the film; a second exposure will be
made in 5.8.
5.6 Remove
the U section of coaxial GR connectors con-
necting the step out and signal in. Position each L connector
(made from the U connector) in the ‘‘STEP OUT’’ and ‘‘SIG-
NAL IN’’ connectors.
5.7
Connect
the test specimen, one end to the ‘‘Step Out’’
and the other end to ‘‘Signal In’’ (see Figure 6).
5.8
The
trace on the TDR screen will have moved to the
right from its original position in 5.5. Mark the position of the
leading edge of the pulse on the horizontal graticule (again at
10% of pulse height). At this time, a second exposure on the
same film used in 5.5 can be made. This will result in both
traces on one film. The distance between this mark and the
mark in 5.5 is the measured propagation delay (TD). Multiply
the measured T
D
by
20 (distance/time set at 20 ns/cm), then
IPC-2-5-19-1-4
Figure
2 Sample Hanging Device
IPC-2-5-19-2
Figure
3 Cable Preparation
IPC-2-5-19-3
Figure
4 Cable Connection
IPC-TM-650
Number
2.5.19
Subject
Propagation
Delay of Flat Cables Using Time Domain
Reflectometer
Date
7/84
Revision
A
P
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divide
the result by 10 (distance/time magnifier set at 10) to
get the total T
D
of
the test specimen. Subtract 0.20 ns x 2 =
0.40 ns delay caused by the connection device used at each
end of the test cable and divide this result by the exact length
of the test specimen to get the propagation delay in ns/0.3 m.
IPC-2-5-19-4
Figure
5 Dual Exposure Picture TDR Trace
IPC-2-5-19-6
Figure
6 Test Cable Hookup
IPC-TM-650
Number
2.5.19
Subject
Propagation
Delay of Flat Cables Using Time Domain
Reflectometer
Date
7/84
Revision
A
P
age3of3
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ