Solar Electronics 9354-2 - Application Notes; Direct Injection; Indirect Injection; Impedance

Solar Electronics Company
9. APPLICATION NOTES
1 Direct Injection - Generally direct injection is part of a subsystem/equipment conducted
susceptibility or vulnerability testing and is applied between an isolated equipment case
and ground or from a connector pin to the connector shell. In most cases the required
direct injection level is lower than the maximum capability of the generator. Therefore, a
resistive network can be developed externally to adjust the output impedance and
provide the required open circuit voltage and/or peak circuit current specified by the
designated test procedure.
2 Indirect Injection - (Consider isolated case injection) The Type 9335-2 Multi-port
coupling Device along with other injection probes are inductive coupling devices used
for system susceptibility testing and applied to the subsystem/equipment
interconnecting cables. The inductive coupling device (transformer) provides more
latitude in the development of the required output impedance.
Consider the previous example of the generator port 1 with the 25 ohm output
impedance. The 2:1 step down port 2 of the Type 9335-2 or similar type of two turn
injection probes (primary) could be (secondary) of about 6.25 ohms. As stated in the
example, resistors may be used to adjust the output impedance to 5 ohms. Also a special
injection probe with segmented cores could be built to produce the 5 ohm output
impedance without resistors.
3 Impedance - There may be occasions when the existing output impedance of the
Transient Generator may be inappropriate for a specific test procedure of the
specification requirement. Since the generator impedances are a function of frequency
and waveform; no single output impedance could be selected without sacrificing
performance. However, because of the available power, many other impedances at
different open circuit voltages and peak circuit currents may be developed external to the
generator (with the proper resistive network or transformer).
If for example the generated open circuit voltage is 3200 volts and peak circuit current is
128 amps, the output impedance would be 25 ohms. By externally adding a series 22
ohm resistor from the output connector center conductor to a shunt 5.6 ohms that is
connected to the connector ground, the open circuit voltage at the junction of the 22 ohm
and 5.6 ohm is 340 volts and the peak circuit current is 68 amps. This results in a output
impedance of 5 ohms.