IPC-TM-650 EN 2022 试验方法.pdf - 第608页
6 Notes 6.1 The TDR employs a pulse rise time less than 250 pico- seconds. A pulse of this rise time is extremely rich in harmon- ics extending well into the GHz region of the frequency spec- trum. The impedance probe il…
4.6
Coaxial Cable
Impedance:
50 - 2Ω RG-58A, RG-58C,
or equivalent; Termination: GR874 connectors, both ends;
Length: approximately 61 cm
4.7
Load
General
Radio type GR874 or equivalent 50Ω
load. This is an optional item, which is used to calibrate the
TDR.
5
Procedure
5.1
Allow
a minimum of one hour for TDR warm-up and
calibrate the instrument per manufacturer’s instructions.
5.2
Prepare
the test specimen by stripping approximately 13
mm of insulation from one end of cable. Separate the ground
and signal conductors and solder a copper buss across the
grounds (see Figure 5).
5.3
Adjust
the TDR settings as follows:
Vertical: 0.1 e/cm
Distance/time: 20 ns/cm.
Magnifier: 50 x (For equipment other than Hewlett-Packard,
use settings as close as possible to these.)
Insert the 30 cm air line into the output of the TDR. This will
serve as the 50Ω reference. Attach the coaxial cable to the air
line and terminate with the impedance probe. Vertically center
the 50Ω reference line on the TDR graticule.
5.4
Press
the probe against the conductor to be tested
insuring the ground of the probe is against the cable ground
(see Figure 5) and check the vertical placement of the 50Ω
reference; re-center if necessary.
5.5
Adjust
the distance/time magnifier to 5 or 10 and rotate
the magnifier delay dial until the total length of the cable is vis-
ible on the screen. Measure the vertical reflection coefficient
(e) in cm as illustrated in Figure 2.
5.7
Calculate
the characteristic impedance (Z
0
)
as follows:
Z
0
= 50
(
1 + e
1 − e
)
(Ω)
Calculate
Z
0
of
the cable measuring as shown in Figure 2.
Calculate Z
0
max., e = e max;
Z
0
min., e = e min.
IPC-2-5-18-3
Figure
4 Cable Connection Device. Refer circled items to parts list. Made from General Radio Co. Type 874-C62A.
IPC-TM-650
Number
2.5.18
Subject
Characteristic
Impedance Flat Cables (Unbalanced)
Date
7/84
Revision
B
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6 Notes
6.1
The
TDR employs a pulse rise time less than 250 pico-
seconds. A pulse of this rise time is extremely rich in harmon-
ics extending well into the GHz region of the frequency spec-
trum. The impedance probe illustrated in Figure 1 is designed
to minimize the effects of impedance mismatch at the con-
nection; therefore, it is suggested that a probe of this type be
used for the impedance measurement. The importance of a
good connection between the cable under test and the TDR
can not be overemphasized.
Cables longer than3minlength may be tested, but care
must be exercised so as not to confuse the effect of increased
wire resistance with an apparent increase in impedance as the
magnifier delay dial is rotated to observe the longer cable
length (function of attenuation, which includes wire size).
6.2
Under
no circumstances should the cable be tested
while in a coiled form due to the effect of increased induc-
tance.
6.3
Keep
cable a minimum of 15 cm away from any dielec-
tric or ground plane including metal, wood, etc. (except in
step 5.5).
6.4
Measurement
of Z
0
of
unknown cable length should be
made as close as possible to the cable connection device
(after overshoot and undershoot).
6.5
The
reference Z
0
cable
may be positioned after the
RG58C cable and before the cable connection device. There-
fore, the reference Z
0
is
adjacent to the test cable on the TDR
trace.
IPC-2-5-18-4
Figure
5 Connection of Impedance Probe to Sample
under Test
IPC-TM-650
Number
2.5.18
Subject
Characteristic
Impedance Flat Cables (Unbalanced)
Date
7/84
Revision
B
P
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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.
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