Chapter 2 - Electromagnetic Compatibility

Question 1

What is a common mode unwanted signal?

Answer 1

Common mode is an interference on the signal due to noise formed by the victim circuit and the ground plane.

Question 2

What is differential mode unwanted signal?

Answer 2

Differential mode signals are coupled into a pair of conductors because of radiation from an EMI source. It can also be a result of coupling between a given conductor and its return path. Twisting conductors can minimize differential mode interference.

Question 3

How can common mode signals affect equipment?

Answer 3

• It can directly affect equipment operation, because the CM signal gets inside the equipment and causes logical errors.
• CM signal can be converted to a DM signal by the cable or equipment.

Question 4

For telecommunications cabling within joint-use tunnels, it is recommended to use an overall longitudinal balance of ___ at higher frequencies (e.g., 1-300 MHz)

A) less than 30 dB
B) 30 dB to 40 dB or greater
C) 60 dB or greater

Answer 4

B) 30 dB to 40 dB or greater

Question 5

For telecommunications cabling within joint-use tunnels, it is recommended to use an overall longitudinal balance of ___ at lower frequencies (e.g., voice)

A) less than 30 dB
B) 30 dB to 40 dB or greater
C) 60 dB or greater

Answer 5

C) 60 dB or greater

Question 6

In order to measure electromagnetic compatibility (EMC), we measure the electrical and magnetic field strength of the outgoing radiation to determine radiated emissions. What is the unit of measure for electric field strength? What about magnetic field strength?

Answer 6

Electric field strength is : volts/meter

Magnetic field strength is : amperes/meter

Question 7

What frequency spectrum is conducted interference normally measured?

Answer 7

100kHz to 30Mhz

Question 8

What frequency spectrum is usually taken to measure radiated interference?

Answer 8

30 MHz to 5 GHz

Question 9

What are the 12 bands of the electromagnetic spectrum recognized by ITU from 3 Hz to 3 THz?

Answer 9

ELF (Extremely Low Frequency) Band 1
SLF (Super Low Frequency) Band 2
VF (ULF) (Ultra Low Frequency) Band 3
VLF (Very Low Frequency) Band 4
LF (Low Frequency) Band 5
MF (Medium Frequency) Band 6
HF (High Frequency) Band 7
VHF (Very High Frequency) Band 8
UHF (Ultra High Frequency) Band 9
SHF (Super High Frequency) Band 10
EHF (Extremely High Frequency) Band 11
THZ Band 12

Question 10

An electromagnetic field is an area of energy that surrounds electrical devices. It is a combination of an electric field (created by _____) and magnetic fields (created by_____).

Answer 10

electric field: stationary charges

magnetic field: moving charges (electric currents)

Question 11

What is the minimum separation distance recommended between frequency induction heating and metallic cabling?

Answer 11

39in

Question 12

What is the minimum separation distance recommended between arc welders and metallic cabling?

Answer 12

31 in

Question 13

What is the minimum separation distance recommended between lamps and metallic cabling?

Answer 13

5 in

Question 14

What is the minimum separation distance recommended from possible sources of EMI exceeding 5kVA for:

unshielded power lines in proximity to non-metal conduit

unshielded power lines in proximity to metal conduit

power lines in grounded metal conduit in proximity to grounded metal pathway

electric motors and transformers

Answer 14

unshielded power lines in proximity to non-metal conduit: 24in

unshielded power lines in proximity to metal conduit: 12in

power lines in grounded metal conduit in proximity to grounded metal pathway: 6in

electric motors and transformers: 48in