SOLAR ELECTRONICS COMPANY
APPENDIX
Investigation of Current Waveform Distortion
Through Magnetic Coupling Devices into Short Circuits.
Background
Several customers, engineers, and technicians have expressed difficulty in producing the DO-160, Section
22, Waveform 1, the 70 μS double exponential current waveform from either Waveform 2, the 6.4 us
voltage waveform, or Waveform 4, the 70 μS voltage waveform of the Transient Pulse Generator through
the Multi-port Coupling Device (which was only designed for the coupling of the damped sine-wave and
generators with different source impedances) into a short circuit or (0.1 Ω non-inductive resistor).
Although it is written in Section 22 under Waveform 2 that ideally the voltage waveform of Waveform 2
would produce the short circuit current waveform of Waveform 1 through an inductive transformer; no
special coupling device has yet been identified that could demonstrate the concept. Therefore, until the
unique device becomes available we will try to explain the problems and provide some solutions.
Identifying the Problems
The first thing was to duplicate the Test Setup, reproduce the waveform distortion, and try to identify the
source of the problem. After duplicating the Test Setup, the Transient Pulse Generator output was
measured to verify that it provided the required 70 μS open circuit voltage of 1600 Vpk and when
matched with a 2 Ω load the voltage output dropped to approximately half or 800 Vpk. When the
generator was connected to Port 2 (2:1) of the Multi-port Coupling Device in a calibration fixture and the
output voltage waveform measured across one of the fixture's two 50 Ω terminations, the pulse width
was reduced (24 μS), and the unsaturated voltage was limited (30 Vpk). This was believed to be from
insufficient core cross section, inductive reactance, and resistive loading of the primary. When the
fixture's terminations were replaced with shorts (0.1 & 0.01 Ω) and the waveform measured with a
clamp-on current probe, the waveform was distorted even though the pulse width was slightly wider (30
μS). The distortion and increase in pulse width was attributed to the Multi-port Coupling Device's
increase in secondary loading, which increased the bandwidth, circuit current, and premature core
saturation. However, it was later determined that both the Multi-port Coupling Device (injection probe)
and the current probe (reception probe) had similar low frequencies deficiencies, which made the
problem appear even worse.
Providing a Solution
Since the voltage and the current waveforms must be the same across a resistor; to eliminate the
distortion from the reception probe and help identify the major contributor(s) to the problem, a non-
inductive 0.1 Ω resistor was connected in series with the calibration loop and the voltage waveform
measured across the resistor using a calibrated scope. The waveform was plotted and the peak current
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