MIL-STD-461G CS101: Ripple Injection on Power Leads, Step by Step

Standards & compliance · 3 min read · 16 cited facts

CS101 is the conducted susceptibility test in MIL-STD-461G (11 December 2015) that injects audio-frequency ripple in series with the equipment's power leads, from 30 Hz to 150 kHz. It also has an exit that first-time readers miss: compliance is reached either by holding the specified voltage at the EUT's input, or — where the EUT's input impedance will not let the voltage get there — by driving a precalibrated power level into a fixed load.

Applicability is broader than most people expect: AC inputs drawing up to 30 A per phase, and all DC inputs regardless of current (CS101). On a shipboard or ground-vehicle programme, that puts the DC buses in scope by default.

The limit

The injection chain, step by step

• Feed the EUT from its own clean supply through 50 µH LISNs (§4.3.6), sized to the platform power type. The LISNs set the source impedance the limit assumes.
• Couple the ripple in series with the power lead through a coupling transformer.
• Drive the transformer with a signal generator and power amplifier chain, or with a programmable source that provides built-in ripple and interharmonic injection.
• Sweep 30 Hz to 150 kHz, holding Limit Curve #1 (136 dBµV, ≈6.3 V RMS) for nominal source voltages above 28 V, or Limit Curve #2 (126 dBµV, ≈2.0 V RMS) at 28 V and below.
• If the voltage limit cannot be reached, apply the alternative compliance route: a precalibrated 80 W into 0.5 Ω, falling to 0.09 W at 150 kHz.

Both curves roll off toward the top of the band — 106.5 dBµV on Curve #1 and 96.5 dBµV on Curve #2 at 150 kHz — so the drive chain's task eases exactly where amplifier and transformer response start to fall away.

Where CS101 stops

CS114, CS115, CS116 and CS117 use dedicated transient generators rather than programmable sources, and they are out of scope for this article. A programmable source with ripple injection covers CS101; it does not cover the rest of the conducted susceptibility suite, and a purchase made on the assumption that it does buys the wrong instrument. CS101 also does none of the work of a power quality standard — no 400 Hz waveform synthesis, no reliability duration testing, no grid ride-through.