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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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Certificaton of test tracks according to ISO This alternative should therefore be avoided and can only be used if a potential overestimation of the exposure index up bgc a factor of is taken into account.
In the following, the results of WPM in the time domain are assumed to be the correct assessment results:. To eliminate this effect initially, the frequency f p of the field quantity change is investigated in two regions:. There is a noticeable sustained oscillation at a frequency of approximately 3 kHz, which slowly rises and falls in amplitude and which has maximum amplitude but negative sign at about the same time as byv step occurs.
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. It is worth knowing that EI noise also increases proportionally to the square root of the measurement system bandwidth.
This means that the reference levels actually are only increased by the factor V. DFT is also based on a sampled time signal rather than a continuous time signal. The effect of this parameter, therefore, also needs to be discussed. Eqn 9 describes the induction mechanism in the frequency domain:.
They cause artifacts that lead b111 incorrect assessment results. Noise and vibration protection. If another step occurred after the first one shown, these strong oscillations and the slower decay would lead to large over- or underestimations depending on the point in time and the sign of the second field step.
Isotropic probes capture all three orthogonal field components simultaneously. The measurements or calculations of the expected electromagnetic fields are the basis of the expert opinions. So at low frequencies, it is sufficient and necessary to limit the maximum value of the slope only. However, the artifacts here are even more pronounced, leading to an even larger underestimation by a bvg of 0. It is, however, dangerous and unreasonable to reduce the cutoff frequency of the band-limiting low-pass filter or the sampling rate unnecessarily.
The step responses of such weighting filters and the weighting filter made up from first order filter elements gbv shown in Fig. Rueckerl C, Eichhorn Hgv. 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.
This could, however, result in an overestimation if several field sources are present because the maximum values could occur at different points in time such that the RSS value of the maximum values may never actually be reached at any given time. It is also necessary to use a sufficiently long transformation frame.
Let T i be the duration of the field quantity changes plus the duration of the subsequent pause. The work cannot be changed in any way or used commercially without permission from the journal. Thus, the usual W f that emulates the bv physical and biological effects accurately, and can be realized using first order filter elements, is not always used.
Published online May 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 fast convolution technique.
Insertion loss of silencers.
National Center for Biotechnology InformationU. The time signal g t is itself periodic with a period duration T g and T is an integer multiple of T g ; and. The signal is therefore underestimated when compared to the first order high-pass filter realization. This factor lies between unity and V max and depends on the crest factor of the signal.
Find articles by Helmut Keller. Situation 2 often occurs when assessing pulsed signals such as those encountered with welding equipment. The following filter made up from a cascade of first order filters is a very good approximation for the reference levels of the Low ALs for magnetic flux density:. Where there are several field sources with different polarizations, however, all three eigenvalues will have significant values, and the reduction to only one component can bgvv lead to a significant underestimation.
The DC component must be assessed separately. If rectangular direct current DC impulses are used as an internal electrical field strength stimulus, a stimulation effect does not b1 until the amplitude of the internal field strength exceeds the threshold value e T.
The result of fast convolution using DFT is the same as if the selected frame of the time signal g t were repeated with a period duration of T and a true convolution with w t were to take place. Dynamic stiffness of impact sound insulation.