Download EMC Filters Attenuation Measuring Method

PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012
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EMC Filters Attenuation Measuring Method
Kazimierz Piwowarczyk, Marian Wnuk, Leszek Nowosielski,
Rafal Przesmycki, and Marek Bugaj
Faculty of Electronics, Military University of Technology
Gen. S. Kaliskiego 2 str., 00-908 Warsaw, Poland
Abstract— The aim of this work is to present the attenuation measurement procedure measurement and laboratory stand for filters used to interference suppression in power and telecommunication lines. The procedure is based on the CISPR 17:2000 standard. The article describes
the attenuation measurement system for filter with impedance different then 50 Ω. The article
presents the measured attenuation characteristics of set of EMC filters which are offered on the
market. The calibration of measurement method is presented too.
1. INTRODUCTION
Electromagnetic compatibility (EMC) is the ability of an electronic system or subsystem to reliably
operate in its intended electromagnetic environment without either responding to electrical noise or
generating unwanted electrical noise. Electromagnetic interference (EMI) is the impairment of the
performance of an electronic system or subsystem by an unwanted electromagnetic disturbance.
In general the public mains power supply voltage waveform is sinusoidal, which means that
it includes only the fundamental frequency (50 or 60 Hz) without any harmonic multiples of this
frequency. Purely resistive circuits such as filament lamps or heaters, when powered from the
mains, draw a current that is directly proportional to the applied voltage, and do not create any
extra harmonic components. By contrast, non-linear circuits do draw a non-sinusoidal current,
despite the applied voltage being sinusoidal. All non-linear currents, however, will cause harmonics
currents, i.e., currents with frequencies that are integer multiples of the supply frequency.
Traditionally, harmonic pollution was only a concern for larger installations, particularly for
power generation and distribution and heavy industry. But the modern proliferation of small
electronic devices, each drawing perhaps only a few tens or hundreds of watts of mains power, and
usually single-phase (such as personal computers), has brought the problem of mains harmonics
to the fore even in domestic and commercial applications. Of all the above examples, it is the
electronic DC power supplies that are causing the most concern due to the increasing numbers
of electronic devices such as TV sets in domestic premises, information technology equipment in
commercial buildings and adjustable-speed drives in industry [1].
2. ELECTRICAL SPECIFICATIONS OF FILTERS
Where indicated, the component values in the datasheets are nominal values. The actual values
can vary from the indicated ones based on the electrical tolerances given by the manufacturers.
The test conditions for the components are listed below.
Current ratings of EMI filters are determined by the individual filter components. Since current
flow leads to a temperature rise in passive components, the ambient temperature of the environment
where the filter is to be used has a direct impact on the rated current. The nominal currents stated
for our components refer to an ambient temperature of 0N = 40◦ C or 0N = 50◦ C as indicated
on the component and in this catalog. The maximum operating current at any other ambient
temperature Θ can be calculated by means of the formula (1).
r
θmax − θact
I = IN ·
(1)
θmax − θN
where: IN — rated current at θN , θact — actual ambient temperature, θN — temperature at which
the rated current is defined, θmax — rated maximum temperature of the component,
Voltage. When looking at voltage ratings, care needs to be taken not to confuse the voltage
rating of the filter with the nominal voltage of the power grid. The most common nominal voltages
are defined in IEC 60038. A European power grid, for example, has a defined nominal voltage of
230 V ± 10%. The maximum voltage at the terminals can therefore be 230 V + 10% = 253 V.
DC resistance. The DC resistance of the filter is the resistance measured at the relevant
power network frequency, i.e., 50 Hz for European applications and at a defined temperature, such
as 25◦ C.
Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 27–30, 2012
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3. MEASUREMENT METHODS
Generally, to suppress power line and signal line emission, some form of filtering is required. Filter
attenuation is highly dependent upon source and load impedances. Manufacturers’ data is generally
published for 50 Ω source and load impedances while actual impedances are generally reactive and
vary considerably over the frequency range of interest. While there are methods for determining
the actual impedances, these values are usually unknown. Hence, the selection of filters through
mathematical computation is usually impractical.
An alternative approach is that of impedance mismatch. That is, if a filter mismatches its source
and load impedances, minimum transfer of signal (EMI) power will occur. If the source impedance
is high, the filter input impedance should be low, or shunts capacitive. If the source impedance is
low, the filter input impedance should be high, or series reactive. The same mismatch should exist
between the load impedance and the filter’s output impedance [2].
Another consideration is whether the EMI is common mode or differential mode, where common
mode refers to noise voltages on two conductors referenced to ground, and differential mode refers
to a voltage present on one conductor referenced to the other. In many cases both types of EMI
must be attenuated. Virtually all off-the-shelf power line filters are designed to handle common
mode noise, and many provide both common and differential mode filtering. Without conducted
emission test data, it is generally difficult to determine the interference mode of the equipment and
thus the type of filter required.
3.1. The Classic Method of Measuring
The method is based on measuring the efficiency of filters used to suppress disturbances in the
supply lines and data lines. Measurement frequency range is in the band from 30 MHz to 950 MHz
(the method is acceptable and correct to the frequency of 5 MHz). The measurement is carried out
in an anechoic chamber. This allows get the most exact results without interference from other
devices working.
Filters are generally described by their attenuation, also called insertion loss. In order to determine the attenuation, a defined source and load are connected and the signal from the source
is measured. The filter is then inserted and the measurement repeated. The attenuation is then
calculated from the two results by means of the formula (2).
n [dB] = 20 log
E1
E2
(2)
where: n — attenuation [dB], E1 — the results with the filter, E2 — the results without the filter.
Interference accompanied current flowing in the circuit. It can be assumed that they have
the same value but are in opposite phase relative to the second line. In the case of a symmetric
measurement of attenuation is measured between two lines (L and N ) through a symmetrical
transformer. Wire mass (E) is not used during this measurement. In the asymmetrical attenuation
Figure 1: Classic laboratory stand.
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PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012
Figure 2: Block diagram of the test bench — standardization measurement.
Figure 3: Block diagram of the test bench — proper
measurement.
Figure 4: The measuring position prepared for conducting standardization measurement.
measurement method has the same phase as opposed to the line, but its value may be different
depending on the output circuit. For this method the two lines (L and N ) are connected together
and the measurement is done in relation to the mass of the circuit (E) in the system. The concept
of laboratory stand of shows the block diagram in Figure 1.
3.2. The Proper Method of Measuring
In to identify attenuation of individual power lines L and N well connected to them filters should
be measured attenuation the individual circuits are installed on the destination solution design.
Tests should be performed on the filters installed in the destination chamber shielding. Since it
is not known input impedance tested power supply lines L and N , the measurements should be
performed in the measurement system takes into account the differences in input impedance test
circuit (impedances different from 50 Ω) in relation to the input impedance of the measurement
system used in devices like signal generator and receiver measurement (impedance equal to 50 Ω).
In Figure 2 and Figure 3 shows the proposed measurement systems to take account of differences
in impedance.
Each of these configurations should be treated as a separate measuring circuit. After the measurement for standardizing the proper measurement should be done. In the place where during
the standardization measurement the measurement receiver was connected the 50 Ω load must be
connected. Filter attenuation is the difference between the measured signal levels in the function
of frequency.
Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 27–30, 2012
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4. LABORATORY STAND
Constructed measuring stand should enable the measurement of attenuation filters. Measurements
will be done according with the recommendations of the PN-CISPR 17:2000 in the frequency range
from 10 kHz to 6 GHz. Table 1 shows the apparatus used for measuring the EMC filters. Figure 4
shows the measuring position prepared for conducting standardization measurement. Necessary
the control software automates the measurement process.
5. MEASUREMENT RESULTS
In order to validate the work of the measuring system measured the attenuation of attenuator BN
745394 (Figure 4). Figure 5 shows the attenuation values obtained.
Figure 6 shows the measured values of attenuation power supply filter. Figure 7 shows the
measured values attenuation of signal filters.
Table 1: List of equipment.
No.
Device Name
Manufacturer
Type
1
PC
HP
DV3600
Serial Number
-
2
Signal generator
Rohde & Schwarz
SMB 100A
100587
3
Reciver
Rohde & Schwarz
ESIB 26
-
4
Broadband load 50 Ω
Agilent
909F
51500
5
Attenuator
Spinner; HP
BN 745394
-
6
Filters
Schaffner
Schaffner
Schaffner
Corcom
Conec
FN 686-25-23
FN 700Z-20-03
FN 2070-3-06
F 7426-3
MAP1XAAAH02R
-
7
Converter USB/GPIB
Agilent
82357A
MY43457984
30
Attenuation [dB]
20
10
0
-10 0,00001
0,0001
0,001
0,01
0,1
-20
1
10
f [GHz]
-30
-40
standardization measurement
proper measurement
attenuation
Figure 5: Attenuation attenuator BN 745394 (20 dB).
Figure 6: Attenuation power supply filters.
Figure 7: Attenuation signal filters.
PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012
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6. CONCLUSIONS
Based on measurement results we can state that the laboratory stand built on the basis of Electromagnetic Compatibility Laboratory Military University of Technology equipment is working
properly. The measured attenuation of attenuator and power supply and signal filters are similar
to the manufacturer’s specifications.
ACKNOWLEDGMENT
The research work financed from the financial funds assigned to the science in the years 2010/2011
as the development work. The research work is realized in Poland.
REFERENCES
1.
2.
3.
4.
“Basics in EMC and power quality,” www.schafner.com.
“EMI shielding design guide,” www.tecknit.com.
Ott, H. W., Electromagnetic Compatibility Engineering, A John Wiley & Sons, INC., 2009.
CISPR 17:2000, “Methods of measurement of the suppression characteristics of passive radio
interference filters and suppression components,” 2000.