EN 50444:2008

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Basic standard for the evaluation of human exposure to electromagnetic fields from equipment for arc welding and allied processesNorme de base pour l'évaluation de l'exposition des personnes aux champs électromagnétiques d'un équipement pour le soudage à l'arc et les techniques connexesGrundnorm zur Ermittlung der Exposition von Personen gegenüber elektromagnetischen Feldern von Einrichtungen zum Lichtbogenschweißen und artverwandten Prozessen25.160.10Varilni postopki in varjenjeWelding processes13.280Varstvo pred sevanjemRadiation protectionICS:SIST EN 50444:2008en,fr,deTa slovenski standard je istoveten z:EN 50444:200801-junij-2008SIST EN 50444:2008SLOVENSKI
STANDARD
EUROPEAN STANDARD EN 50444 NORME EUROPÉENNE
EUROPÄISCHE NORM February 2008
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2008 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50444:2008 E
ICS 13.280; 25.160.10
English version
Basic standard for the evaluation of human exposure
to electromagnetic fields from equipment
for arc welding and allied processes
Norme de base pour l'évaluation
de l'exposition des personnes
aux champs électromagnétiques
d'un équipement pour le soudage à l'arc et les techniques connexes
Grundnorm zur Ermittlung der Exposition von Personen gegenüber elektromagnetischen Feldern von Einrichtungen zum Lichtbogenschweißen und artverwandten Prozessen
This European Standard was approved by CENELEC on 2008-02-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

The text of the draft was submitted to the formal vote and was approved by CENELEC as EN 50444 on 2008-02-01. The following dates were fixed: – latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement
(dop)
2009-02-01 – latest date by which the national standards conflicting with the EN have to be withdrawn
(dow)
2011-02-01 This European Standard is to be read in conjunction with EN 50445. This European Standard has been prepared under mandates M/305 and M/351 given to CENELEC by the European Commission and the European Free Trade Association. __________

– 3 – EN 50444:2008 Contents 1 Scope.6 2 Normative references.6 3 Terms and definitions.6 3.1 General.6 3.2 Specific for arc welding and similar applications.8 4 Physical quantities, units and constants.9 4.1 Quantities and units.9 4.2 Constants.9 5 Assessment procedures.9 5.1 Arc welding equipment components to be tested.9 5.2 Assessment conditions.9 5.3 Averaging.9 5.4 Pulsed or non-sinusoidal welding current.9 5.4.1 General.9 5.4.2 Summation for basic restriction assessment.10 5.4.2.1 Summation of current density components without phase information.10 5.4.2.2 Summation of currents density components including phase information.10 5.4.2.3 Summation of specific absorption rate (SAR) components.11 5.4.3 Summation for reference level assessment.11 5.4.3.1 Summation for stimulation effects without phase information.11 5.4.3.2 Effective reference level method.12 5.4.3.3 Summation for stimulation effects including phase information.13 5.4.3.4 Summation for thermal effects.13 5.4.4 Equivalent frequency of induced current density waveforms.13 5.5 Conductivity of living tissue.14 5.6 Frequency range limitations.14 5.7 Application of assessment procedures.15 5.8 Measurements.16 5.8.1 Measuring equipment.16 5.8.2 Static field measurements.17 5.8.3 Time domain field measurements.17 5.8.4 Broadband field measurements.17 5.8.5 Frequency selective field measurements.17 5.8.6 Time domain weighted field measurements.18 5.9 Analytical calculations.18 5.9.1 General information.18 5.9.2 Derivation of magnetic field based on welding current.18 5.9.3 Derivation of induced current density based on magnetic field.19

Assessment parameters.26 Annex B (informative)
Examples for exposure assessment.30 Annex C (informative)
Numerical simulation using anatomical body models.39 Annex D (informative)
Geometry factor and field gradients.43 Annex E (informative)
Welding current ripple assessment.44 Annex F (informative)
Summation using first order filter weighting functions.46 Annex G (informative)
Example for an uncertainty budget.50 Bibliography.51

– 5 – EN 50444:2008 Figures Figure 1 – Average electrical conductivities for homogeneous body modelling from 10 Hz to 10 MHz.14 Figure A.1 – Probe position for measurement on welding cables.27 Figure A.2 – Topology of welding cable for numerical simulations.28 Figure B.1 – Probe position during measurement.31 Figure B.2 – Planar current density distribution in the disk.32 Figure B.3 – Welding current waveform and calculation parameters.33 Figure B.4 – Induced current density derived from welding current.33 Figure B.5 – Spectral components of welding current pulse.34 Figure B.6 – Summation of induced current density components with phase information.35 Figure B.7 – Flux density waveform and r.m.s. values of the spectral components.35 Figure B.8 – Flux density waveform and r.m.s. values of the spectral components.36 Figure B.9 – Summation of flux density components with phase information.37 Figure B.10 – Flux density waveform and r.m.s. values of the spectral components.37 Figure D.1 – Planar field distribution for different cable arrangements at I2 = 200 A.43 Figure E.1 – Spectral analysis of triangular function.44 Figure F.1 – Magnetic flux density reference levels, filter and tabulated values.47 Figure F.2 – Weighting function phase angles for B and H, filter and tabulated values.47 Figure F.3 – Induced current density basic restrictions, filter and tabulated values.48 Figure F.4 – Weighting function phase angles for J, filter and tabulated values.49 Figure F.5 – Comparison of results for example B.7 (first order filter left, tabulated values right).49 Tables Table 1 – Permissible assessment procedures for arc welding equipment.15 Table 2 – Permissible assessment procedures for welding cables.16 Table 3 – Reasonable expanded assessment uncertainties.24 Table A.1 – Typical parameters for tests with pulsed welding current.26 Table B.1 – Induced current density components and phase angles.34 Table B.2 – Flux density components.35 Table B.3 – Flux density components and phase angles.36 Table B.4 – Flux density components and fractional contributions.38 Table C.1 – Electrical conductivity of tissue types.41 Table E.1 – J simulation results for relevant spectral components (r.m.s. values).45 Table E.2 – B calculation results for relevant spectral components (r.m.s. values).45 Table G.1 – Example uncertainty budget for broadband field measurement.50

Generic standard to demonstrate the compliance of electronic and electrical apparatus with the basic restrictions related to human exposure to electromagnetic fields (0 Hz – 300 GHz) EN 50445
Product family standard to demonstrate compliance of equipment for resistance welding, arc welding and allied processes with the basic restrictions related to human exposure to electromagnetic fields (0 Hz – 300 GHz) EN 60974-1
Arc welding equipment – Part 1: Welding power sources
(IEC 60974-1) 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 General 3.1.1 basic restrictions restrictions on exposure to electric, magnetic and electromagnetic fields that are based directly on established health effects and biological considerations 3.1.2 conductivity (σ) ratio of the conduction current density in a medium to the electric field strength 3.1.3 contact current current flowing into the body by touching a conductive object in an electromagnetic field

– 7 – EN 50444:2008 3.1.4 effective reference level (BL,eff) level, provided for practical exposure assessment purposes using a broadband measurement, derived from frequency dependent reference levels considering the spectral content of the field 3.1.5 EMF electric, magnetic or electromagnetic field 3.1.6 exposure situation that occurs when a person is subjected to electric, magnetic or electromagnetic fields or to contact current other than those originating from physiological processes in the body and other natural phenomena 3.1.7 exposure level value of the quantity evaluated when a person is exposed to electromagnetic fields or contact currents 3.1.8 induced current density (J) electromagnetic field induced current per unit area inside the body 3.1.9 magnetic flux density (B) magnitude of a field vector that is equal to the magnetic field H multiplied by the permeability µ of the medium
B = µ H (1) 3.1.10 magnetic field strength (H) magnitude of a field vector in a point that results in a force Fr on a charge q moving with velocity vr
Fr = q (vrx µ Hr) (2)
or magnetic flux density divided by permeability of the medium 3.1.11 permeability (µ) property of a material which defines the relationship between magnetic flux density B and magnetic field strength H NOTE It is commonly used as the combination of the permeability of free space µ0 and the relative permeability µR for specific dielectric materials
µ = µR µ0
(3)
where
µ is the permeability of the medium expressed in Henry per metre (H m-1). 3.1.12 point of investigation (POI) location in space at which the value of E-field, H-field or power density is evaluated NOTE This location is defined in Cartesian, cylindrical or spherical co-ordinates relative to the reference point on the EUT.

Expression in time domain
∫=TdttXTX02r.m.s.)(1 (4) where X(t) is the signal at time t; T is the signal period or multiples of it. Expression in frequency domain
∑=nnXX2r.m.s. (5) where
Xn is the magnitude of spectral component at nth frequency, expressed as r.m.s. value. 3.1.14 reference levels directly measurable quantities, derived from basic restrictions, provided for practical exposure assessment purposes NOTE Respect of the reference levels will ensure respect of the relevant basic restriction. If the reference levels are exceeded, it does not necessarily follow that the basic restriction will be exceeded. 3.2 Specific for arc welding and similar applications 3.2.1 arc welding power source equipment for supplying current and voltage and having the required characteristics suitable for arc welding and allied processes NOTE 1 An arc welding power source may also supply services to other equipment and auxiliaries e.g. auxiliary power, cooling liquid, consumable arc welding electrode and gas to shield the arc and the welding area. NOTE 2 In the following text, the term “welding power source” is used. 3.2.2 industrial and professional use use intended only for experts or instructed persons 3.2.3 expert (competent person, skilled person) person who can judge the work assigned and recognize possible hazards on the basis of professional training, knowledge, experience and knowledge of the relevant equipment NOTE Several years of practice in the relevant technical field may be taken into consideration in assessment of professional training. 3.2.4 instructed person person informed about the tasks assigned and about the possible hazards involved in neglectful behaviour NOTE If necessary, the person has undergone some training.

– 9 – EN 50444:2008 3.2.5 rated maximum welding current (I2max) maximum value of the conventional welding current that can be obtained at the conventional welding condition from a welding power source at its maximum setting 4 Physical quantities, units and constants 4.1 Quantities and units The internationally accepted SI units are used throughout this document. Quantity Symbol Unit Dimension Current density J Ampere per square metre A m-2 Electric conductivity σ Siemens per metre S m-1 Frequency ƒ Hertz Hz Magnetic field strength H Ampere per metre A m-1 Magnetic flux density B Tesla T (Vs m-2) Permeability µ Henry per metre H m-1 4.2 Constants Physical Constant Symbol Magnitude Permeability of free space µ0 4π ⋅10-7 H m-1 5 Assessment procedures 5.1 Arc welding equipment components to be tested The main source of EMF is the welding current, delivered by the power source, flowing through the welding circuit. The parameters of the current e.g. amplitude and waveform, which are determined by the welding power source only, have the greatest influence on the exposure level. Therefore assessment shall be based on these parameters and the configuration of the welding circuit as specified in this standard. However, direct emissions from components of the welding system e.g. wire feeders may also contribute to the total EMF and shall be considered. Care shall be taken not to add emissions assessed at short distances (less than 1 m), as the welder will not be close to those components at the same time. 5.2 Assessment conditions Test configurations, distances, operating conditions and other parameters, which are valid for all evaluation procedures, are specified in Annex A. 5.3 Averaging Time and spatial averaging shall be made in accordance with the relevant document containing limits. 5.4 Pulsed or non-sinusoidal welding current 5.4.1 General For pulsed or non-sinusoidal (including a d.c. component) welding current a separate assessment for a.c. and d.c. components shall be made. Only the a.c. component shall be used to assess compliance with restrictions for time varying fields. The d.c. component shall be used to assess compliance with restrictions for static fields.

∑==MHzHziiLitJJJ101, (6) where Jt
is the total relative induced current density, expressed as a fraction of the permissible value Ji
is the induced current density component at frequency ƒI; JL,i
is the corresponding current density limit at frequency ƒi; The sum of the weighted spectral components shall not exceed 1. As no phase information is used in this summation formula, this method can lead to significant overestimation of exposure. When information on the phase-angles of spectral components is available, the procedure given in 5.4.2.2 may be applied. 5.4.2.2 Summation of currents density components including phase information As the spectral components of a pulsed or non-sinusoidal signal are typically not in phase (i.e. they do not reach their maximum value at the same time in the time domain), Equation (6) provides a conservative approach to the assessment of exposure. Therefore Equation (7) may be used for a more realistic summation whenever the phases of the spectral components are available.

– 11 – EN 50444:2008 The sum of the weighted spectral components shall not exceed 1 at any time t within the evaluation interval, which shall be one period of the pulsed or non-sinusoidal signal. The time increments used for evaluation shall be less than or equal to 1/10 of the period of the highest relevant spectral component.
1)2cos(,≤++∑iiiiiLitfJJϕθπ (7) where Ji
is the induced current density spectral component at frequency ƒI; JL,i
is the corresponding current density limit at frequency ƒi, see Annex F; ƒi
is the frequency of the spectral component i (components up to 10 MHz maximum) ; θi
is the phase angle of the spectral component at frequency ƒI; ϕi
is the phase angle of the weighting function at frequency ƒi, see Annex F. 5.4.2.3 Summation of specific absorption rate (SAR) components Thermal effects due to EMF will be negligible for most types of arc welding equipment. If relevant spectral components (see 5.4.1) in the frequency range (see 5.6) above 100 kHz exist, Equation (8) shall be applied for summation of SAR spectral components.
∑==GHzkHziiLitSARSARSAR10100, (8) where SARt
is the total SAR, expressed as a fraction of the permissible value; SARi
is the SAR spectral component at frequency ƒI; SARL,i
is the corresponding SAR limit at frequency ƒi. 5.4.3 Summation for reference level assessment 5.4.3.1 Summation for stimulation effects without phase information For summation of magnetic field strength spectral components with respect to stimulation effects, Equation (9) may be applied.
∑∑+==MHzfifHziiLitscoscobHHHH101, (9) where Ht
is the total relative magnetic field strength, expressed as a fraction of the permissible value; ƒsco
is the summation cut off frequency in accordance with the reference document for the limit values;
Hi
is the magnetic field strength component at frequency ƒi; HL,i
is the corresponding magnetic field strength reference level at frequency ƒi; b
is the permissible magnetic field strength value defined in the reference document for the limit values.

∑∑+==MHzfifHziiLitscoscobBBBB101, (10) where Bt
is the total relative magnetic flux density, expressed as a fraction of the permissible value; ƒsco
is the summation cut off frequency in accordance with the reference document for the limit values; Bi
is the magnetic flux density component at frequency ƒI; BL,i
is the corresponding magnetic flux density reference level at frequency ƒI; b
is the permissible magnetic flux density value defined in the reference document for the limit values. An example for a summation without phases is given in B.8. 5.4.3.2 Effective reference level method The assessment is performed by measuring the total r.m.s. magnetic flux density value using a broadband probe. For evaluation of exposure the result of the broadband measurement is compared to the calculated effective reference level BL,eff. The spectral content of the field shall be derived, e.g. by Fast Fourier Transformation (FFT) of the measured field or, alternatively in case of field measurements around welding cables, the measured welding current. The contribution of each spectral component is calculated as a fraction of the total a.c. r.m.s. flux density or welding current value. The r.m.s. effective reference level is obtained using Equation (11)
∑=iiLieffLBFB,,1 (11) where BL,i
is the corresponding r.m.s. magnetic flux density reference level at frequency ƒi; Fi
is the fractional contribution of the spectral component i, defined as
....,..smrismriBBF= (12) where Br.m.s.
is the total r.m.s. magnetic flux density value, Br.m.s.,i
is the r.m.s. value of the spectral component i; or
smrismriIIF.,.= (13) where Ir.m.s.
is the total r.m.s. welding current value, Ir.m.s.,i
is the r.m.s. value of the spectral component i. NOTE Further guidance may be found in the NRPB document W24 “Occupational Exposure to Electric and Magnetic Fields in the Context of the ICNIRP Guidelines” [4]. An example using this method is given in B.10.

– 13 – EN 50444:2008 5.4.3.3 Summation for stimulation effects including phase information As the spectral components of a pulsed or non-sinusoidal signal are typically not in phase (i.e. they do not reach their maximum value at he same time in the time domain), the procedure in accordance with 5.4.3.1 provides a conservative approach to the assessment of exposure. Therefore Equation (14) may be used for a more realistic summation whenever the phases of the spectral components are available. Equation (14) may be used for evaluation of B or H values. The sum of the weighted spectral components must not exceed 1 at any time t within the evaluation interval, which shall be one period of the pulsed or non-sinusoidal signal. The time increments used for evaluation shall be less than or equal to 1/10 of the period of the highest relevant spectral component.
1)2cos(≤++∑iiiiiitfLAϕθπ (14) where Ai
is the amplitude of the spectral component at frequency ƒi; Li
is the applicable limit at frequency ƒi, or above ƒsco the value b as given in the reference document for the limit values, see Annex F; ƒi
is the frequency of the spectral component i (components up to 10 MHz maximum); θi
is the phase angle of the spectral component at frequency ƒi; ϕi
is the phase angle of the weighting function at frequency ƒi, see Annex F. Examples for summation including phase information are given in B.8 and B.9. 5.4.3.4 Summation for thermal effects Thermal effects due to EMF will be negligible for most types of arc welding equipment. If relevant spectral components (see 5.4.1) in the frequency range (see 5.6) above 100 kHz exist, Equation (15) shall be applied for summation of magnetic flux density spectral components.
∑∑+==GHzfiLifkHziditscoscoBBBB3002,1002 (15) where Bt is the total relative magnetic flux density, expressed as a fraction of the permissible value; ƒsco is the summation cut off frequency according to the reference document for the limit values; Bi
is the magnetic flux density component at frequency ƒi; BL,i
is the corresponding magnetic flux density reference level at frequency ƒi; d is the magnetic flux density value defined in the reference document for the limit values. 5.4.4 Equivalent frequency of induced current density waveforms If the reference document contains frequency dependent limits, the peak value of the induced current density may be compared to the corresponding limit for a equivalent frequency ƒe, which is calculated as defined in Equation (16)
pefτ21= (16) where τp is the pulse duration of the induced current density waveform.

Figure 1 – Average electrical conductivities for homogeneous body modelling from 10 Hz to 10 MHz The average values in Figure 1, combined with the application of homogeneous body models, provide a conservative approach to the assessment of exposure. Therefore the uncertainty for these values shall be taken as 1 % when numbers with two decimal places are used for calculation. 5.6 Frequency range limitations Evaluations, dependent on the type of welding current waveform, shall be made in the relevant frequency range from 0 Hz (d.c., as applicable) to an upper frequency defined as the highest applicable value of a) for d.c. welding current: − 1 kHz for single phase transformer-rectifier types; − 3 kHz for three phase transformer-rectifier types; − 10 times the ripple frequency for inverter types, b) for sinusoidal a.c. welding current: − 10 times the a.c. welding current frequency; − 10 times the ripple frequency for inverter types, c) for pulsed or non-sinusoidal a.c. welding current: − the frequency ƒmax defined by the minimum rise or fall time τp min of the maximum welding current
I2max;
minmax4110pfτ= (17) − 10 times the ripple frequency for inverter types.

– 15 – EN 50444:2008 The manufacturer, based on his knowledge of the process or special techniques used in the apparatus, shall select a higher upper frequency if applicable. NOTE These frequency range limitations are based on prior experience of measurements made on arc welding equipment. 5.7 Application of assessment procedures As some procedures are not appropriate to be used for assessment of specific types of emission, the following tables give guidance for the selection of assessment procedures. Only one of the methods listed in Tables 1 and 2 for a.c. and d.c. components (where applicable) for each exposure type and component shall be used, as selected by the manufacturer. Some methods represent a conservative approach to the assessment of exposure and therefore an overestimation may occur. Further information may be found in the paragraphs describing the various procedures. Table 1 – Permissible assessment procedures for arc welding equipment Welding current Assessment procedure
d.c. component Assessment procedure a.c. component Static field measurements to show compliance with reference levels (5.8.2) Time domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) d.c. Time-domain field measurements to show compliance with reference levels (5.8.3) Time domain weighted field measurements to show compliance with reference levels (5.8.6) Time domain field measurements to show compliance with reference levels (5.8.3) Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) a.c. sinusoidal Not applicable Time-domain weighted field measurements to show compliance with reference levels (5.8.6) Static field measurements to show compliance with reference levels (5.8.2) Time domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) Time domain weighted field measurements to show compliance with reference levels (5.8.6) Pulsed or a.c. non-sinusoidal Time-domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Analytical or numerical calculations based on time-domain field measurements to show compliance with basic restrictions (5.9.3 or 5.10.3)

d.c. component Assessment procedure
a.c. component Static field measurements to show compliance with reference levels (5.8.2) Time domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Time-domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) Time domain weighted field measurements to show compliance with reference levels (5.8.6) Analytical or numerical calculations to show compliance with reference levels (5.9.2 or 5.10.2) d.c. Analytical or numerical calculations to show compliance with reference levels (5.9.2 or 5.10.2) Analytical or numerical calculations to show compliance with basic restrictions (5.9.3, 5.10.3 or 5.10.4) Time domain field measurements to show compliance with reference levels (5.8.3) Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) Time domain weighted field measurements to show compliance with reference levels (5.8.6) Analytical or numerical calculations to show compliance with reference levels (5.9.2 or 5.10.2) a.c. sinusoidal Not applicable Analytical or numerical calculations to show compliance with basic restrictions (5.9.3, 5.10.3 or 5.10.4) Static field measurements to show compliance with reference levels (5.8.2) Time domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Time-domain field measurements (5.8.3) in combination with spectral analysis to show compliance with reference levels Broadband field measurements to show compliance with reference levels (5.8.4) Frequency selective field measurements to show compliance with reference levels (5.8.5) Time domain weighted field measurements to show compliance with reference levels (5.8.6) Analytical or numerical calculations to show compliance with reference levels (5.9.2 or 5.10.2) Pulsed or a.c. non-sinusoidal Analytical or numerical calculations to show compliance with reference levels (5.9.2 or 5.10.2) Analytical or numerical calculations to show compliance with basic restrictions (5.9.3, 5.10.3 or 5.10.4)
5.8 Measurements 5.8.1 Measuring equipment Instrumentation used to measure exposure levels should be built according to IEC 61786 (0 Hz to 9 kHz) [37], EN 61566 (100 kHz to 1 GHz) [33] or equivalent specifications. The measuring instrumentation shall cover the frequency range of emissions from the equipment under test. However more than one instrument may be used to achieve that. Measuring instruments used for direct evaluation with respect to reference levels may have a frequency dependent response that correlates with the frequency dependent limit values (see 5.8.6).

– 17 – EN 50444:2008 In order to fully characterise the exposure conditions it may be necessary to use several instruments including broadband current-sensors, field probes, oscilloscopes, test receivers or spectrum analysers. The measuring instrumentation used for welding current or field measurements must cover the whole frequency range of emissions from the equipment under test. Splitting of frequency ranges is allowed. If more than one instrument is used to cover the total frequency range, care must be taken to ensure that overlapping frequency sub-ranges do not lead to an overestimation of the levels. The reference sensor for magnetic field measurements, used for the evaluation of compliance with Reference Levels, shall consist of three mutually perpendicular concentric coils with a measuring area of (100 ± 5) cm² to provide isotropic sensitivity. The outside diameter of this reference sensor shall not exceed 13 cm. Successive measurements using a single coil probe shall not be used for the final evaluation process. Other probes may be used, but in case of doubt the values obtained with the reference sensor take precedence. The total value of the magnetic field is calculated by taking the square root of the sum of the squared amplitudes of the three field components, measured in orthogonal directions. This ensures that the measured value is independent of the direction of the magnetic field. The reference sensor for magnetic field measurements, used to gather input data for numerical calculations according to 5.10.3, shall consist of three mutually perpendicular concentric coils with a much smaller measuring area (e.g. 3 cm²) than the reference sensor used for reference level assessment to be able to detect local field strength maxima without averaging effects over large measuring areas. The outside diameter of this reference sensor shall not exceed 3 cm. Successive measurements using a single coil probe shall not be used. Other probes may be used, but in case of doubt the values obtained with the reference sensor take precedence. Possible out of band responses of the probes used for measurements of time-varying fields have to be considered as well as saturation effects and other possible sources for measuring errors. 5.8.2 Static field measurements For this type of measurement pure static field or time domain sensors may be used. If applicable, according to 5.3, time averaging shall be applied before comparing the results to the relevant limits. 5.8.3 Time domain field measurements This type of measurement may be used to evaluate static or sinusoidal (single frequency) magnetic fields without further analysis. For comparison to reference levels for time varying fields a conversion of the measured peak value to the r.m.s. value is necessary. The results may also be used for further evaluation steps, such as spectral analysis or calculations to derive current density values for comparison with the basic restrictions. 5.8.4 Broadband field measurements Broadband measuring instruments give no spectral information on the measured field. If the limit value is frequency dependent, a conservative approach is to compare the measured value, which is the total field strength of all spectral components within the measurement bandwidth, to the lowest reference level value inside this bandwidth. Another approach, which gives less conservative results, is to use the effective reference level method in accordance with 5.4.3.2. 5.8.5 Frequen
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