Similar as LISNs being the central components for conducted emission testing, CDNs are essential for conducted immunity test set ups. CDNs are used to couple RF into cables.
Whereas the CISPR standards specify conducted emission measurements, IEC 61000-4-6 is the main standard for conducted immunity testing. IEC 61000-4-6 specifies three coupling devices:
- Coupling Decoupling Networks (CDN)
Coupling via CDN is the most common test method. It requires least power. It is always used, when appropriate CDNs for the type of signal are available.
- EM Clamps
The EM-Clamp is used, when a CDN is not possible, e.g. for shielded or complex cables. The clamp and the separate decoupling clamp are placed around the cable.
- Bulk current injection clamps
Similar use as EM-clamp. A monitoring of the injected current is strongly recommended.
Coupling and decoupling devices shall be used for appropriate coupling of the disturbing signal (over the entire frequency range, with a defined common mode impedance at the EUT port to the various cables connected to the EUT and for preventing applied test signals from affecting other devices, equipment and systems that are not under test.
The preferred coupling and decoupling devices are the CDNs, for reasons of test reproducibility and protection of the AE. Furthermore, CDNs require significantly lower RF power, to achieve the same test levels, compared to EM clamps or BCI clamps.
