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CHAPTER 5: EMI MEASUREMENTS
5.2 Requirements for conducted EMI
Requirements for the measuring setup are defined in [1], which regulates every aspect
of the layout and interconnections of the Equipment Under Test (EUT). For the emis-
sions of Radio Frequency Energy there are several categories in which equipments are
divided in, according to the position within the aircraft, with different limits according
to how sensible the location is. The category in which a matrix converter drive falls is
"L", defined as in the following:
This category is defined for equipment and interconnected wiring located in areas far from aper-
ture of the aircraft (such as windows) and far from radio receiver’s antenna. This category may
be suitable for equipment and associated interconnecting wiring located in the electronic bay of
an aircraft.
The document defines also how the measurements needs to take place, how to inter-
connect the device and how to set-up the instrumentations. The settings defined for
the interference measuring equipment specify that the peak detector function needs to
be selected, with Impulse bandwidth (BWI) of 1kHz; it also cites that the time constant
of the peak detector must be lower or equal to 1ms.
For the interconnections a Line Impedance Stabilization Networks (LISNs) must be
used to feed the EUT, to have a fully characterized source impedance of 50Ω.
It defines the measurement layout, where the current probe needs to be inserted five
centimetres from the EUT, as depicted in Fig. 5.1.
The maximum admissible conducted emissions limits, for the conditions described
above, is within the range 150kHz–30MHz, are shown in Fig. 5.2.
5.3 Probe calibration
The current probe used is a FCC F-35A, which have an operation bandwidth of 100Hz
- 100MHz. This specific probe has a typical transfer impedance of 0 dBΩ between
100kHz and 30MHz, as visible in its calibration curve in Fig. 5.3; this means that with-
out calibration the error introduced will be negligible, but doing this will be a good
practice and the procedure will be useful as a reference for other probes. The calibra-
tion consists in measuring the probe’s output for a reference input signal in the band-
width of interest to obtain experimentally the transfer impedance versus the frequency,
either if the datasheet is not available or to make sure the probe is working properly.
The instruments used during the procedure are a Signal Generator Agilent E8257C and
a spectrum analyser Agilent MXA N9020A.
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