In Germany for example the regulation BGV B11 has to be applied. The safe operation of demagnetizers requires the observance of exposure limits!. Workplaces must be checked for compliance with the regulations of the employers’ liability insurance associations BGV B The measurements or calculations. Health and Safety Regulation on electromagnetic fields (EMFV); The health and safety requirements of the employers’ liability insurance association BGV B
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The induction mechanism described in eqn 8 shows that the internal electric field strength is proportional to the time derivative of the external electric field or magnetic field:.
Because the reference levels are very strongly dependent on frequency, the dynamic range of measurement systems [that digitize s t instead of g t ] is significantly larger.
As already mentioned, WPM fundamentally delivers the same results in the time domain and the frequency domain as long as exactly the same complex transfer function W f is used. Suffice it to say at this point that it may be considered to be definitely not negligible. Impact of the transformed time frame on WPM in the frequency domain The fast convolution on which WPM in the frequency domain is based is performed in practice with the aid of discrete Fourier transformation DFT rather than Fourier transformation.
A DC magnetic field of The following field profile, among others, is used for an example calculation by Rueckerl: Reducing the bandwidth or the sampling rate too much will naturally lead to considerable measurement errors, which must be strictly avoided.
Values of less than unity are permissible. The acronym pwl stands for piecewise linear. The phase can therefore be calculated from the magnitude: This would result in additional large over- or underestimations depending on the point in time and sign of the field changes. WPM is thus relatively sensitive to the intrinsic noise of the b1 system.
This is allowed hgv V equals V max. Measurement systems that use an analog filter for the fundamental weighting high pass filter and digital filters for the remaining filter elements represent a good compromise. The effect of this parameter, therefore, also needs to be discussed.
Electromagnetic environmental compatibility
Since an AD converter can only capture a finite signal amplitude without strong distortion, there will always be a value EI max up to which measurements can be made reliably. The solutions used in state-of-the-art equipment have been demonstrated. The method can be used without limitations for any field profile and emulates the underlying physical and biological effects significantly better than all other presently known methods.
Once again, it is clear here that the result of WPM in the frequency domain is usually strongly distorted by the artifacts associated with the piecewise linear W f. In particular, WPM in the time domain can be used without a second thought.
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BGM gives a correct assessment for signal segments with a field change of the form ; and. The sampling rate used in such a measurement system must be at least twice the cutoff frequency of the band-limiting low-pass filter to avoid artifacts due to undersampling. Published online May If it is to be realized digitally, it is sensible to build it as a cascade of first order IIR filters.
Certificaton of test tracks according to ISO Rueckerl C, Eichhorn KF. The disadvantages of competing methods are demonstrated. The permissible amplitude of the sinusoidal signal is now higher by the factor Vbut the permissible RMS value of the pulsed signal remains the same as that of the non-pulsed signal.
The frequency range is divided into segments for which eqn 7 is valid:. Published by Wolters Kluwer Health, Inc. Arch Ital Biol The sampling frequency of the digital filter must be chosen much higher than 3 kHz, however, so that the analog high pass filter with 3 kHz cutoff frequency can be approximated without any significant deviations. This peak value is a measure of the exposure and is designated as the exposure index EI European Commission However, the artifacts here are even more pronounced, leading to an even larger underestimation by a factor of 0.
No appreciable errors occur if all three of the following conditions are concurrently met:. In contrast, filters that can be formed from a cascade of first order filter elements emulate the underlying effects much more realistically.
This field probe must be carefully aligned for the maximum bgc index EI according to the polarization and angle of incidence of the field if an underestimation of the exposure situation is to be avoided. The maximum hold function can be reset before the measurement to exclude older results.
Because BGM is worded very intricately and only covers specific examples, eqn 26 is naturally not an exact description of BGM. Footnotes The author declares no conflicts of interest. Summary of WPM in the frequency domain Gbv in the frequency domain produces the same correct results as WPM in the time domain if the following three conditions are met concurrently: Intrinsic noise and dynamic range All measurement systems have intrinsic noise.
Electromagnetic environmental compatibility – Müller-BBM GmbH
It actually already reacts before the stimulating step occurs. The effective length of the impulse response can thus be described very well by a T w that is in the order of five times the time constant. Berufsgenossenschaft der Feinmechanik und Elektrotechnik.
It is also still identical to the first order high bggv filter at the start but shows strong oscillations and decays much more slowly.
The simple reason for this is that the fast convolution cannot be calculated until g t has already been stored. In other words, the magnitude of s t in the single axis version b111 replaced by the RSS value root of the sum of squares of the three weighted time signals, derived from the three time signals of the three orthogonal field components. The effects of sampling apply to all assessment methods though, because nowadays all measurement systems work with values sampled at discrete times.
This would at bggv be true if the amplifiers and AD converters are equivalent and the field probes used are equally sensitive. However, no conclusions relevant to this discussion can be drawn from this fact. A constant component is always suppressed by this high-pass filter. If g t actually consists only of segments that correspond exactly to these four curve forms, BGM can be used.
Alternatively, the exposure index could be determined separately for the three individual components and the RSS value from these three partial results considered as the overall result.