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CW and pulsed mode transfer impedance measurements in coaxial cables
Abstract
Transfer impedance measurements have been performed both in
frequency and time domains. CW measurements were performed using a
matched triaxial system, a quintaxial system, and stripline injection.
For nuclear electromagnetic pulse (NEMP) purposes, measurements up to a
maximum frequency of 200 MHz are sufficient. For this frequency range
the matched triaxial system was found to be the most convenient.
Amplitude and phase measurements in different cables are discussed.
Direct and indirect injection was employed in the time domain
measurements. A delayed coupling is demonstrated when the diffusion term
is dominant in the transfer impedance. In a magnetically shielded cable,
hysteresis and saturation effects have been observed. At 5 kA the
transfer impedance of the magnetically shielded cable increased by an
order of magnitude due to saturation
... Two methods for determining transfer impedance have been recommended by the International Electrotechnical Commission (IEC): the triaxial method [1] and the line injection method [2]. In addition, pulsed mode measurements have also been performed using a matched triaxial system by Goldstrin [3]. Oskari designed a triaxial cell to provide reliable measurements under high thermal and mechanical stresses [4]. ...
With the growing use of custom shielded cables in advanced electronic systems, evaluation of the transfer impedance of shielded cables with non‐standard characteristic impedances is increasingly necessary; however, traditional measurement methods here are limited by the difficulty of obtaining matched loads. This letter presents a method for characterizing the transfer impedance of electrically short shielded cables with an arbitrary characteristic impedance. The proposed method can be used with mismatched loads in the experimental configuration. Validation is performed with cables of known transfer impedance. The presented results closely align with the theoretical formulas.
The Compact Muon Solenoid (CMS) is one of the four high-energy physics experiments for the LHC. Describing the electromagnetic (EM) environment of CMS is of major importance for determining and solving problems related to electromagnetic interference, grounding and shielding. This thesis addresses the EMC studies conducted for the CMS experiment to define the baseline of the future CMS EMC policy. The EMC study has been focused on the power supply distribution system. For that purpose, a simplified scheme of the power supply system has been used in this research work to address EMC studies. These studies are mainly focused on the quantification of the FEE sensitivity to conductive noise coupled through the input/output cables, the noise generated by power supplies and the noise propagation effects present in the detector. Also, the magnitude and effects of transient signals disturbing the power supply system are introduced.
This paper reports a time domain pulse technique for measuring the minimum shielding effectiveness of coaxial cable assemblies. Experimental data for coaxial cable assemblies are presented and compared. The paper also presents a simplified circuit model to simulate the experiment, which confirms the validity of the measurement scheme. At high frequencies, this method of measuring shielding effectiveness is demonstrated to be a more reliable and time-effective alternative to well-known frequency domain techniques
The paper presents a method to determine the complex cable
transfer impedance of shielded cables. This method is based on a
combination of measurements and computations and allows one to handle
multiwire cables too. Some curves of the complex transfer impedance for
coaxial and multiconductor cables are presented. The coupling phenomena
in inhomogeneous cable arrangements are discussed. The screen of a cable
loop is excited by an external source and the signal which couples into
the cable is calculated and measured. The calculation uses the
determined cable transfer impedances. In the frequency domain an
excitation by a second loop is discussed. For direct excitation results
are presented in the time domain
We present the work carried out in the SOBITS project executed
within the framework of the European Measurement and Testing program.
The goal of the project was to compare different methods for
characterization of the shielding performance of board-to-backplane and
backplane-to-cable connectors used in telecommunication and computer
systems. Four measurement methods have been selected. Dedicated test
samples have been designed and developed in order to enable the
measurement of the shielding characteristics of the connectors under
test with all methods. Different shielding configurations were
considered, in order to determine the influence of the quality of the
shield. Single-ended as well as differential excitations have been
considered. Among the test samples, a nonshielded version was designed
for each signal/ground configurations. This sample was used as a
reference. The definition of the quantities that describe the shielding
performance is different for each of the measurement methods. Conversion
formulas between these quantities have been formulated. They were
verified by measuring a reference device that is easy to measure by all
methods. Thus we were able to compare the relative shielding
effectiveness of the various shielded board-to-backplane and
backplane-to-cable connectors for all four measurement methods. The
relative shielding effectiveness of a shielded connector was calculated
with respect to the nonshielded version. We also compared the different
shielding performance results obtained with each measurement method
individually
Two performance parameters of a cable or connector shield are its
surface transfer impedance ZT and its surface transfer
admittance YT. A new method for measuring these properties is
presented. The use of two different terminations for the cable or
conductor under test (CUT) allows one to determine both ZT
and YT. Through characterization of the inner and outer
transmission lines of the triaxial cell, using time domain
reflectrometry, ZT and YT can be determined in
amplitude as well as in phase. The phase is obtained by de-embedding the
measured S-parameters up to the CUT. The de-embedding of the
measurements also allows one to extend the frequency range up to 3 GHz.
To illustrate this method a solid shield with a circular aperture and a
coaxial cable with a braided shield have been measured and compared,
respectively, with theoretical predictions and published results
Definitions of transfer impedance Z//T, through capacitance C//T, normalized through elastance K//T and capacitive coupling impedance Z//F are presented. The coupling equations through a screen as function of these parameters are given and discussed introducing the concepts of equivalent transfer impedance Z//T//E, cut-off frequency f//c and cut-off cable length l//c. The definition of screening attenuation a//s is examined. Z//T, Z//F and Z//T//E are considered as primary quantities, defining the quality of a screen, while a//s should be given as additional information in rated conditions. The correct interpretation of cable screen parameters and of screening test data is considered.
A comparative test program is described which are based on the triaxial set-up as a reference measurement standard. The deviation between the wire injection and triaxial test results are within plus or minus 6 dB, typically plus or minus 4 dB. The plus or minus 6 dB corresponds to the typical accuracy of cable screening tests. The only significant difference between wire injection and triaxial circuit is that a local transfer impedance (on the circumference of the CUT) is measured with the wire injection set-up. In case of a totally unknown CUT, it is best to take at least three measurements at 120 degree apart around the circumference of the CUT. The wire injection set-up simulates closely a practical installation case and the test results represent the practical worst case condition. In contrast, the triaxial set-up test results represent a more or less averaged condition.
The fundamental phenomena involved in the screening of braided cables are discussed and knowledge of these is shown to aid in improving this screening as expressed in terms of surface transfer impedance. It is shown how the use of magnetic materials between two braids, coupled with knowledge of the above optimization techniques, can lead to enormously improved screening which can be maintained by proper application of the magnetic tape. © 1979, The Institution of Electrical Engineers. All rights reserved.
In the measurement of screening of cables and connectors it is found that a dedicated instrument working in the time domain has many advantages over a swept frequency set-up. Comparison is made using calibration circuits to simulate the screening properties of connectors as well as on genuine cable assemblies. Using the simplest possible relationship between time and frequency domains, quite good agreement can be reached whether the measurement is made on a calibrator or a real connector. The conversion can be used on the homogeneous screen of a semi-rigid cable if care is taken in its application.
Experimental evidence for porpoising coupling and optimization in braided cables
- L O Hoeft
- J S Hofstra
- R J Peel
L.O. Hoeft, J.S. Hofstra, and R.J. Peel, " Experimental evidence for porpoising coupling and optimization in braided cables, " Int. Cor$ Electromagn. Compat., Zurich, Switzerland, 1989. [I21 B. Demoulin, P. Degauque, and R. Gabillard, " Transient response of braided-wire shields, " presented at the IEEE Int. Symp. Electromagn. Compat., San Diego, CA, 1979.
On the interference immunity of coaxial cables, " pre-sented at the IEEE Eurocon
- E P Fowler
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Simple and accurate screening measurements on RF cables up to 3 GHz
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Coupling to Shielded Cables
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Proc. IEEE Int. Symp. Electromagn. Compat.
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