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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Inconsistency of a recently proposed method for assessing magnetic field exposure for protection against peripheral nerve stimulation in occupational situations. Open in a separate window.
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FEM model updating and optimisation. Author information Copyright and License information Disclaimer. For this reason, the W f based on first btv filter elements should always be used, even for WPM in the frequency domain. The phase is taken into account in WPM, so an overestimation cannot occur; and.
The parameter k in eqn 8 represents a coupling factor. The step responses of such weighting filters and the weighting filter made up from first order filter elements are shown in Fig.
This would at least be true if the amplifiers and AD converters are equivalent and the field probes used are equally sensitive.
The peculiarities that need to be taken into account when applying WPM in the frequency domain are therefore not discussed until later in this article.
BGM converts the piecewise linear reference levels for magnetic flux density into similarly piecewise linear reference levels for the time derivative of the magnetic flux density. The external magnetic field g t is normally zero.
One way to overcome all the problems associated with the selection of a proper time frame and window function is to perform the WPM in the frequency domain with the aid of a real-time bv convolution technique. If realized in analog form, it can be formed from a network consisting only of resistors and capacitors. Frequency-dependent reference levels R f are used to specify the permitted exposure of persons to external electromagnetic fields.
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. The signal is therefore underestimated when compared to the first order high-pass filter realization. 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. Limiting V to V max is justified by an alleged but otherwise unexplained safety n11 with very short pulses.
The electric field strength e t within the body determines the stimulation effect. This simple model can thus be described by a weighting filter with transfer function W f and a subsequent peak value detector, where:.
If this EI is distinctly less that the EI of the low frequency instrument, it is sufficient to use the EI of b111 low frequency instrument. Only the signal after the high-pass filter is relevant to stimulation, and its magnitude must be compared with the stimulation threshold e 0.
In cases where T i is greater than 1 bgg, T i is set equal to 1 s. 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. In particular, there is no point in trying to extend WPM so that it also evaluates the DC components. The problem here is that the areas of g t that lead to the maximum EI are often not readily identifiable. Applied biolelectricity—from electro stimulation to electropathology.
To some degree, the effect of the DC components is based on 1b1 different physical or biological effects than for the AC components. However, there is no justification for this underestimation based bgg physical or biological grounds. If it is to be realized digitally, it is sensible to build it as a cascade of first order IIR filters.
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Reducing the bandwidth or the sampling rate too much will naturally lead to considerable measurement errors, which must be strictly avoided. It is difficult to imagine an easier way of measuring the exposure index. However, it is actually the case that the rule for the field quantity swing only applies to field characteristics free of DC components and then only for field quantity swings within the same sign.