CID Electromagnetic Compatibility & EMI Control 2

Question 1

In CISPR 32 and FCC Part 15 emissions testing, what is the key difference between Class A and Class B limits?

Accepted Answer

Class B limits are stricter and apply to residential equipment; Class A applies to commercial/industrial

Answer

Class B limits are more stringent and apply to equipment intended for use in residential environments, while Class A limits apply to commercial and industrial settings where more interference may be tolerable.

Question 2

A common-mode choke in a cable assembly primarily attenuates:

Accepted Answer

Common-mode currents flowing in the same direction on both conductors

Answer

A common-mode choke presents high impedance to currents flowing in the same direction (common-mode) while passing differential signals largely unimpaired, suppressing conducted EMI.

Question 3

What is the primary EMC advantage of a multilayer PCB with dedicated ground and power planes over a two-layer board?

Accepted Answer

Reduced loop inductance of the power distribution and signal return paths

Answer

Dedicated reference planes in multilayer boards create a very low inductance power distribution network and minimise the area of signal return current loops, dramatically reducing both radiated and conducted EMI.

Question 4

Which cable routing technique most reduces radiated emissions from an interconnect cable acting as an unintentional antenna?

Accepted Answer

Bundling cables together and routing them tightly along a grounded chassis

Answer

Routing cables along a grounded chassis provides a nearby return path that reduces loop area and shields the cable from radiating, significantly lowering EMI.

Question 5

When performing conducted emissions measurements per CISPR standards, a LISN (Line Impedance Stabilization Network) is used to:

Accepted Answer

Provide a defined, repeatable impedance at the AC input of the EUT and couple EMI to the measurement receiver

Answer

A LISN standardizes the impedance seen at the power port of the equipment under test and provides a safe, calibrated coupling point for the spectrum analyzer or receiver to measure conducted emissions.

(CID) Certified Interconnect Designer Practice Test

(CID) Certified Interconnect Designer Practice Test

CID Electromagnetic Compatibility & EMI Control 2