APEMC 2015
Inter-laboratory Comparison Between CISPR25 Chambers, Identification of Influent Parameters and Analysis by 3D Simulation Frédéric Lafon#1, Josselin Davalan#2, Renaud Dupendant#3 #
VALEO VEEM 2 Rue André Boulle, 94042 Creteil Cedex - France 1
[email protected] [email protected] 3
[email protected] 2
Abstract— In automotive industry, the reference standard used to perform radiated emissions measurements is the CISPR25 [1]. Previous works [2-5] already pointed out that between different labs supposed to be CISPR25 compliant, test results obtained on simple equipment could differ quite significantly (more than 10 dB reported). We identified in [2,3] some parameters at the origin of these deviations, linked to the degrees of freedom in the chamber setup definition in CISPR25. A simultaneous analysis based on the inter-laboratory measurements results linked to the chambers definitions and analysis performed with 3D simulation allowed to establish what are the main influent parameters and their significance. This paper exposes the measurements results and analysis over 13 labs as well as the correlation with 3D simulation to justify about the influence of these parameters individually considered.
I. INTRODUCTION CISPR25 Ed.4 is currently in the standardization process, and plan to include an annex relative to chamber validation. This annex permits to compare measurement results on a standardized source with 3D simulation reference data in order to verify that 90% of points are within ± 6 dB deviation. In order to be prepared to this validation process and to have a better understanding of the dispersions existing between labs, Valeo decided to launch an inter comparison program between its 13 main labs. First step of the work was performed by simulation to define the reference data and to analyze the influence of some key parameters. This work will be exposed in part II. Measurements performed in the labs had been then compared to these reference data and allowed to verify the evaluation performed by 3D simulation. This will be developed in part III. Finally in part IV of this paper we will propose a synthesis as well as recommendation for chamber setup to be considered in CISPR standardization committee in particular. II. ANALYSIS BASED ON 3D SIMULATION Results presented in [2,3] pointed out several parameters’ critical impact: the grounding orientation of the reference plane, the absorbers quality and the reference plane size. In [2,3] we used a “small” dimension emission source [6] (29 cm monopole antenna until 100 MHz and 6 cm above), and
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we wanted to evaluate if these parameters are as much influent with a more representative emission source (1.5 meter length cable). Models developed and simulation specificities are detailed and had been validated in [2,3]. Fig. 2 to 4 show the influence of the reference plane size (between 1m x 2.5m dimensions and 1.5m x 3 m), depending on the absorbers quality and of the source type. These analyses focus on the frequency range up to 200 MHz, being identified as the most critical frequency range where these parameters are influent. This will be exposed in part III of this paper. Full Hybrid : Pyramidal absorbers and ferrite panels
Mixed: Pyramidal absorbers except rear wall in hybrid Perfect : Open area
Fig. 1 A Simulation setups synthesis
With mixed absorbers solution we observed a non negligible impact of the reference plane size with up to 34dB difference. This impact can be however reduced by increasing absorbers efficiency as shown with full hybrid and perfect absorbers results (Fig. 3 and 4). It demonstrates that influent parameters are also linked together. Finally, we can conclude that the nature of the source doesn’t change our conclusions regarding the influence levels of the studied parameters. This last conclusion allows us to consider the comb generator source [6], more easy to use and transfer between labs, to perform measurement and estimate the dispersions between participating labs (with a reduced setup).
APEMC 2015
with mixed absorbers are globally similar. The correlation of this reference plane connection parameter with the absorber performance exists, but is less significant as with the reference plane size. TABLE I SYNTHESIS RESULTS – INFLUENCE OF REFERENCE PLANE CONNECTION DEPENDING ON ABSORBERS PERFORMANCES (10-200 MHZ)
Absorbers Mean deviation Max deviation
Fig. 2: Reference plane size influence (1x2.5m Vs 1.5x3m) in mixed absorber setup and for comb generator source (source) or for 1.5 meter length cable (harness).
Full Hybrid Source Harness 5.5 dB 5.2 dB 17.1 dB 25.3 dB
Mixed Source Harness 5.2 dB 3.9 dB 41 dB 14 dB
Since grounding is not fixed in the CISPR25 this observation leads to the conclusion that two simulated references are needed for measurement data comparison and analysis (1 for horizontal connections and one for vertical ones. The references are simulated with ideal setups (Perfect conductors, perfect absorbers) with the comb generator emission source (Fig.5) and for 1m x 2.5m reference plane size. On the frequency range between 1 MHz and 1 GHz, results are processed as follow: We take maximums over 250 different frequency bands ranging from [1; 1.5] MHz to [950; 1000] MHz. Note that band #100 terminates at 100 MHz. Same technique will be used to analyze the measurements results.
Fig. 3: Reference plane size influence (1x2.5m Vs 1.5x3m) in full hybrid absorber setup and for comb generator source (source) or for 1.5 meter length cable (harness).
Fig. 5: Reference data established by 3D simulation for Vertical or Horizontal grounding connections.
The vertical reference presents resonances below 100MHz being characteristic of this grounding method and confirming the need for two references. We also observed that the resonance level at ~50MHz increases with absorbers efficiency and can also shift depending on ground plane size and length of these connections. For measurement data analysis, the tolerance is defined at ±6dB from the reference corresponding to the setup of the laboratory. Fig. 4: Reference plane size influence (1x2.5m Vs 1.5x3m) in perfect absorber setup and for comb generator source (source) or for 1.5 meter length cable (harness).
The effect of the reference plane connection, either to the wall (Horizontally) or to the floor (Vertically) had been also studied depending on the absorbers performance. This effect had been already partially studied in [2,3] and in [7] for frequencies below 30 MHz. Simulations with full hybrid or
III. INTER LABORATORIES MEASUREMENTS AND ANALYSIS Measurements were performed in 13 laboratories with the similar source (round robin test). Laboratories aren’t identified in this document for confidentiality reasons. In Table II we provide a synthesis of the most significant parameter setup in each of the tested lab.
APEMC 2015
Lab #
1 3 4 6 7 8 13 2 5 9 10 11 12
Reference plane size (mm2) 1500*3000 1020*2540 1500*3000 998*2500 998*2500 990*2500 1500*3000 1020*2600 1000*2500 1000*2000 900*2350 1500*3000 1000*2500
Parameters Grounding Absorbers
Horizontal Horizontal Horizontal Horizontal Horizontal Horizontal Horizontal Vertical Vertical Vertical Vertical Vertical Vertical
CISPR Compliant
Hybrid Pyramidal Pyramidal Ferrite Ferrite Hybrid Hybrid Hybrid Hybrid Ferrite Pyramidal Pyramidal Pyramidal
Yes Yes Yes 1 No 1 No 1 No Yes 1 No Yes 1 No 1 No Yes 2 No
# 100) as discussed for simulations. Their origins are, as expected, due to the parameters discussed in simulation part (grounding, absorbers and reference plane size). Constant deviations above 100MHz are due to error in the antenna reference plane consideration in these labs. 50
Simulation ref ± 6 dB 40 Level (dBµV/m)
TABLE II MAIN PARAMETERS IN STUDIED LABORATORIES
30 20 10 100
150
40
20
0 0
20 Labo2 Labo9 Labo11 Mean Higher limit Vertical
50
40 Band 60
80
100
Labo5 Labo10 Labo12 Lower limit Vertical
Fig. 8: Measurements in labs with vertical grounding (1/2)
60
Simulation ref ± 6 dB
Simulation ref ± 6 dB
40 Level (dBµV/m)
Level (dBµV/m)
250
Simulation ref ± 6 dB Level (dBµV/m)
Fig. 6 to 9 we provide the measurements for each grounding connection technique. Most laboratories are close to the reference tolerances, except “Labo13” for which investigations are still ongoing for this first paper version (Results looking like this laboratory’s reference plane was connected to the floor vertically). Although the characteristic resonances of the vertical grounding do appear, they aren’t of the same amplitude or even at the same frequency in all labs, resulting in consequent deviations from the reference, especially at 50MHz, as shown by the Fig. 8.
200
60
1
: Minor deviations (Reference plane size or height with minor deviation, Rod antenna closer than 1m from absorbers, straps dimensions or spacing too small) 2 : Major deviations (Reference grounding achieved by a single cable)
Band
Fig. 7: Measurements in labs with horizontal grounding (2/2) – Labs identification similar to Fig. 6.
30 20 10 0
20
40
Labo1 Labo4 Labo7 Labo13 Lower limit Horizontal
Band
60
80
100
Labo3 Labo6 Labo8 Mean Higher limit Horizontal
Fig. 6: Measurements in labs with horizontal grounding (1/2)
Major observations can be made: deviations between labs are caused by resonances appearing mainly below 100MHz (band
40
20
0 100
150 Band
200
250
Fig. 9: Measurements in labs with vertical grounding (2/2) - Labs identification similar to Fig. 8.
Laboratories with a horizontal grounding present a higher reproducibility (even for quite different semi anechoic chambers sizes), mostly because this configuration doesn’t induce as much resonances as in vertical. Frequencies at which resonances appear are affected by the chamber configuration and are easily shifted from one lab to another,
APEMC 2015
which explain the high dispersion level observed. Finally we successfully use a reference based on 3D simulation to compare and analyze laboratories measurement results. In order to validate our observations in simulation we focused on comparison between some specific labs. On Fig. 10 we compare labs having similar configuration except for the reference plane size. The deviations between these both laboratories are linked to this parameter and are consistent with what was expected from simulation analysis. 50 45 40 35 30 25 20 15 10
Labo10
Level (dBµV/m)
Labo11
10dB 30
40
some fundamental parameters in the CISPR25 chamber definition, being at the origin of important deviations between CISPR25 compliant labs. These parameters are the reference plane size, the absorbers performance and the grounding connection. Degrees of freedom existing in CISPR25 on these parameters lead to dispersions we exposed and discussed in this paper. Simulation demonstrated that these parameters’ influences are globally the same for a “local” source or with a more realistic emission source (1.5m length harness). We also demonstrated here that the influence of these parameters is interdependent. In order to improve this status, more accurate specifications should be done in CISPR25 or it should at least clearly expose how influent are these parameters considered individually, as suggested on Fig. 12 (corresponding to influence level estimated from 3D simulation, for each parameter, without the interdependently aspect).
16dB 50
60 70 Band
80
90
100
Fig. 10: Investigation on reference plane size influence by measurements
45 Level (dBµV/m)
Labo4 35
Labo9
25 Fig. 12: Synthesis of main parameters influence individually considered in CISPR25 chamber
15
12dB 5 30
40
50
60 70 Band
80
90
100
Fig. 11: Investigation on reference plane connection (Horizontal or Vertical) influence by measurements
On Fig.11, the characteristic resonance due to vertical grounding connection is identified (labo9), and the expected deviation introduced by this parameter between labs is demonstrated by experiments. As introduced in the simulation section, its amplitude is nevertheless not as much important since the absorber performance also influence this phenomenon. We noticed finally that all faraday cages with horizontal connections are with the 6 dB requirement for 9095% of the measured bands, against 80-85% only for the vertical connection. It clearly demonstrates that in the vertical connection setup, we are more sensitive to the others influent parameters identified. IV. CONCLUSIONS In this work, we performed an inter laboratory comparison and for the first time, as far as the authors know, 3D Simulation were used to define the reference data allowing to “validate” and compare the chambers. Up to this mixed approach (mixing simulation with measurements analysis), we made in evidence the influence of
Our recommendations regarding these parameters, finally, to minimize these dispersions are the following: - Only Horizontal connection should be used. - Reference plane size should be 1m x 2m50 (whereas this is difficult to limit its size for practical reasons). - Absorbers performances should be more than 12 dB for the wall behind the reference plane and for all the other walls as soon as the first cavity resonance appears (around 35 MHz typically). REFERENCES [1]
[2]
[3]
[4] [5]
[6] [7]
CISPR25 Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of on-board receivers – Edition 3.0 – 2008. F.Lafon et Al. “Investigation on dispersions between CISPR25 chambers for radiated emissions below 100 MHz” – EMC Europe 2014 – Gotenborg. F.Lafon et Al. “Analysis and discussions regarding dispersions in CISPR25 compliant Faraday cage” – CEM 2014 – Clermont-Ferrand – France. UTAC – Inter laboratory campaign - 04/01399. L.E. Kolb, “Statistical comparison of site-to-site measurement reproducibility”, Electromagnetic Compatibility, 1996. Symposium Record. IEEE 1996 International Symposium on. Comb Generator CG-51 Dr Luke Turnbull, The Ground plane Resonance: Problems with radiated emissions measurements below 30 MHz, in EMCUK 2007 Automotive EMC Conference 2007
