AN3978

EMC requirements

Doc ID 022179 Rev 1

11/19

3

EMC requirements

3.1

Description of the procedure to evaluate the robustness of

the L6370Q

The reference to evaluate the robustness of the L6370Q product is the IEC61131-2

international standard. This international standard gives all the requirements and conditions

of tests that must be performed on the programmable logic controllers (PLC) and their

associated peripherals.

The IEC61131-2 standard specifies the Electromagnetic Compatibility (EMC) requirements

and the nature of the tests to perform in order to determine if the system meets these

requirements (paragraph 7: “Electromagnetic Compatibility EMC Requirements” and

paragraph 8: “Electromagnetic Compatibility (EMC) Type Tests and Verifications” of the Ed2

of the standard). The levels of each test depend on the zone where the system is installed.

The most typical industrial environmental levels correspond to zone B: local power

distribution zone and dedicated power distribution zone (see table 28: “EMC immunity

zones” of the IEC61131-2-Ed2 standard). The following paragraphs recall the test levels for

this zone.

3.2

Burst tests (according to the IEC61000-4-4)

The fast transient burst tests must be applied on all the input pins of the system.

A capacitive clamp-coupling device (50-200 pF) must be used as described in the

IEC61000-4-4 standard. The required burst voltage levels are: analog or digital I/O: +/-1 kV,

dc power line: +/-2 kV. The PLC system continues to operate as intended. Temporary

degradation of the performance is acceptable during the test, but the system must recover

by itself after the test (B criterion according to the IEC61131-2 standard).

3.3

Surge test (according to the IEC61000-4-5)

Since the voltage surge consists of a single but energetic pulse, the L6370Q device embeds

the appropriate protections. Moreover, additional external protection (filter) is necessary, see

Section 2.1 for an example. The absorbed energy complies at least with the requirements of

the IEC61131-2 standard. The high energy surge test must be applied on all output / supply

voltage terminals of the system. For all digital outputs and I/O power, the coupling method is

a 42

Ω serial resistance and a 0.5 μF capacitor. The required voltage surge levels are 0.5 kV

(line-to-line and line-to-earth coupling modes). The PLC system continues to operate as

intended. Temporary degradation of the performance is acceptable during the test, but the

system must recover by itself after the test (B criterion according to the IEC61131-2

standard).