Electromagnetic interference filter

Fig. 10.3. Example of attenuation-frequency plot of electromagnetic interference filters as a function of...

Fig. 10.4. Mounting of electromagnetic interference (EMI) filters inside a shielding box.

As with prisms, there are other devices that have been historically used for dispersing or filtering electromagnetic radiation. These include interference filters and absorption filters. Both of these are used for monochromatic instruments or experiments and find little use compared to more versatile instruments. The interested reader is referred to earlier versions of instrumental analysis texts. 

FIGURE 7.12 Typical electromagnetic interference (EMI) filter schematic and outline the filter yields 60 dB common-mode attenuation and 50 dB transverse mode attenuation between 100 kHz and 1 Mhz. 

Some manufacturers recommend using a filter at the output of the inverter to smooth the waveform applied to the motor and to reduce the sharp rise and fall in the notches that may be present, as in the case of current-fed motors. Steep sided notches cause a high dV/dt across the insulation of the motor, which can reduce the life expectation of the insulation. The filter may also be required to reduce electromagnetic interference (EMI). 

The simplest and most inexpensive way to select certain portions of the electromagnetic spectmm is with a filter. There are two major types, absorption filters and interference filters. Absorption filters can be as simple as a piece of colored glass. In Section 2.1, we discussed how blue glass transmits blue wavelengths of the visible spectmm but absorbs red and yellow wavelengths. This is an example of an absorption filter for isolating... 

Ferrites represent the most widespread technological solution to reduce electromagnetic interference (EMI), because they allow the directly induced noise to be filtered. These ferrimagnetic ceramics produce magnetic flow density in response to small magnetization forces applied. Currently, ferrites used for EMI suppression above 30 MHz are composed of mixtures of oxides of iron,... 

The amplifier circuit should also have extensive filtering of unwanted electromagnetic interference. To eliminate RF interference, filter capacitors should be used in the front end of the amplifier as well as at various stages of the amplifier. Very high frequencies can be... 

The data acquired during the test had to be filtered so that high-frequency content, associated to parasitic vibrations in the table and electromagnetic interference, could be removed. The smooth shape of the experimental curve is therefore associated to the filtering of the records. For succinctness, stage one (time = 0 10) and three (time = 20 30) of the loading phase are presented in Fig. 13, see previous page. 

The near-infrared (NIR) region of the electromagnetic spectrum was discovered by William Her-schel [8] in 1800. However, it was not until the 1950s that suitable sources and sensitive lead sulfide detectors [9] were available for NIR instrumentation. In 1954, engineers at DuPont developed an NIR process analyzer using the newly discovered lead sulfide detector and an Ebert monochromator for dispersion. The same group developed a workhorse NIR process analyzer using the lead sulfide detectors and optical interference filters [10]. 

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