CS101 is applicable to all applications that connect to an external primary power source that is not dedicated to a single device. The test goal is to determine if power line conducted interference over the frequency range of 30 Hz to 150 kHz causes the device performance degradation.
The susceptibility testing pass/fail is now related to the EUT performance with the test limit describing an interference level. In the CS101 case, two test levels are established – 1) a test voltage applied to the EUT or 2) a pre-calibrated drive level based on a 0.5-? load of the interference source.
Figure 5 provides the basic CS101 configuration with the calibration setup used instead of the test setup. The calibration level is a curve over the test frequency range identifying the power dissipation into a 0.5-? resistor for the frequency range. The interfering power source settings are recorded during calibration to be used as the maximum drive if the EUT impedance prevents attaining the test voltage.
During the test, the interfering signal source is adjusted to produce the test voltage measured at the EUT power terminals. Current flows in a loop from the coupling transformer secondary through the EUT and is returned via the power supply mains. As the test frequency increases the LISN impedance increases creating a voltage drop reducing the voltage drop at the EUT. The capacitor across the LISN terminals reduces the LISN voltage by providing a low impedance path for the current loop.
The EUT characteristic impedance controls the voltage drop. If the impedance is low (less than 0.5-?) the test voltage will not be attained with the calibration settings, so the drive level limiting function satisfies the required test level.
The test configuration circuit has a potential to become resonant with significant voltage drops other than across the EUT. If the test voltage is not attained at frequencies below 10 kHz, an investigation is needed to determine where the voltage drop occurs and to implement methods to minimize the effects of non-EUT voltage drops.
Notice that the measurement oscilloscope uses an isolation transformer to prevent accidental grounding of the power line under test. This allows the oscilloscope to become a potential shock hazard if connected to an ungrounded neutral or phase lead. Use caution!
MIL-STD-461G introduced the use of a Power Ripple Detector (PRD) as an alternative to the standard test approach to allow measurement in the frequency domain by separating the power frequency from the interference frequency. This is a convenient means to measure the test voltage, especially at the lower frequencies.
If issues are identified, solutions tend to be somewhat difficult at lower frequencies for AC powered devices reacting to power frequency harmonics. At higher frequencies, filtered connectors or filter inserts can be very effective.