Conducted Emissions Measurements: Current Method

This article is devoted to the current method of the conducted emissions measurements (see [1] for the voltage method). To facilitate the discussion we will concentrate on two standards: DO‑160 (aerospace) and CISPR 25 (automotive). Both standards use a current probe to measure the emissions (see [2] for the current probe measurement details).

DC Conducted Emissions Measurements: DO-160

Both DO-160 and CISPR 25 standards require the conducted emissions measurements be taken in a shielded enclosure like the one shown in Figure 1.

Figure 1: Shielded enclosure for dc conducted emission measurements

DO-160 standard specifies six different categories of devices (B, L, M, H , P, Q) depending on location and separation between the equipment and aircraft radio antennas. Conducted emissions measurements are performed in the frequency range of 150kHz – 152 MHz. Allowable limits for the power lines and interconnecting bundles, for the six categories, are shown in Figures 2 and 3.

Figure 2: DO-160 conducted emissions limits – Categories B, L, M, & H

Figure 3: DO-160 conducted emissions limits – Categories P & Q

DO-160 simplified measurement setup inside the shielded enclosure for the conducted emissions measurements is shown in Figure 4.

Figure 4: DO-160 measurement setup inside the shielded enclosure

A standard 5 µH LISN (with RF measurement port terminated in 50 Ω) can be used with an external 10 µF capacitor. Such a LISN is shown in Figure 5.

Figure 5: DO-160 LISN

DC Conducted Emissions Measurements: CISPR 25

CISPR 25 conducted emissions measurements are performed in the frequency range of 100 kHz – 108 MHz. Allowable limits for the five different classes of devices for the current method of conducted emissions measurements are shown in Figure 6.

Figure 6: CISPR 25 conducted emissions limits (current method)

CISPR 25 measurement setup inside the shielded enclosure for the conducted emissions measurements is shown in Figures 7 and 8.

Figure 7: CISPR 25 measurement setup inside the shielded enclosure (top view)

Figure 8: CISPR 25 measurement setup inside the shielded enclosure (side view)

Note that the measurement setup includes two LISNs. The LISNs act as lowpass filters and provide a constant 50 Ω load on each line (battery and ground). In this aspect, the LISNs perform similar functions to the LISNs used in the CISPR 25 voltage method of conducted emission measurements [1]. There is, however, one major difference with respect to LISNs between the two methods. In the voltage method the LISNs perform the (voltage) measurements of the noise currents, while in the current method the noise (current) measurements are done using the current probes.

Figure 9 shows the physical arrangement inside the shielded enclosure.Figures 10 and 11 show more details of the test setup inside the chamber.

Figure 9: Physical connections inside the shielded enclosure

Figure 10: LISNs and load simulator

Figure 11: Current probe and the EUT

Figures 12 and 13 show the conducted emission measurement results for the EUT in the frequency ranges 0.150 – 6.2 MHz and 26 – 108 MHz, respectively.

Figure 12: Test result – 50 mm position, AVG detector, 150 kHz – 6.2 MHz

Figure 13: Test result – 50 mm position, AVG detector, 26 – 108 MHz

Acknowledgement

The author would like to thank Jim Teune of E3 Compliance LLC for his expert advice.

References

1. Bogdan Adamczyk, “Conducted Emissions Measurements – Voltage Method,” In Compliance Magazine, August 2017.
2. Bogdan Adamczyk, “Current Probe Measurements in EMC Testing,” In Compliance Magazine, September 2017.

Dr. Bogdan Adamczyk is a professor and the director of the EMC Center at Grand Valley State University (GVSU) where he performs EMC precompliance testing for industry and develops EMC educational material. He is also the founder and principal educator of EMC Educational Services LLC (www.emcspectrum.com) which specializes in EMC courses for industry. Prof. Adamczyk is the author of the book “Foundations of Electromagnetic Compatibility with Practical Applications” (Wiley, 2017). He can be reached at profbogdan@emcspectrum.com.