# Chapter 2 - Electromagnetic Compatibility Flashcards

1
Q

To successfully filter both common mode (CM) and differential mode (DM) unwanted signals, the preferred method is:

a. Contact discharge
b. Line coupling
c. Conductor twisting
d. A magnetic scheme

A

d. A magnetic scheme
p. 2-24

To successfully filter both types of unwanted signals, a magnetic scheme is preferred. CM unwanted signal reduction is effective when afflicted lines are coupled together through a ferrite bead. For DM unwanted signal mitigation, individual ferrite beads can be installed on each input lead of the victim line or output lead of the interfering circuit or line.

2
Q

Improper grounding (earthing), poor filtering, and electrical power lines are all examples of _____ that cause EMI problems.

a. Receiving or receptor elements
b. Transfer or propagation sources
c. Conducted and radiated emission sources

A

b. Transfer or propagation sources

p 2-16

```Transfer or propagation sources, including:
–– Space separation.
–– Shielding failures.
–– Poor filtering.
–– Improper grounding (earthing).
–– Electrical power lines.
–– Input/output cabling.```
3
Q

When determining the minimum size of an equipment room (ER), the number of work areas to be served must be multiplied by:

a. 0.023 m2 (0.25 ft2)
b. 0.05 m2 (0.5 ft2)
c. 0.07 m2 (0.75 ft2)
d. 0.09 m2 (1 ft2)

A

c. 0.07 m2 (0.75 ft2)

p 3-39

Multiply the number of work areas to be served by ≈0.07 m2 (0.75 ft2) and the number of BAS devices to be served by ≈0.023 m2 (0.25 ft2) to determine the ER size.

4
Q

As a general requirement, consideration should be given to having a ceiling height of _____ above finished floor (AFF) in telecommunications spaces.

a. 2.4 m (8 ft)
b. 2.74 m (9 ft)
c. 3 m (10 ft)
d. 3.4 m (11 ft)

A

c. 3 m (10 ft)

p 3-3

The minimum ceiling height should be ≈2.4 m (8 ft) AFF. Consideration should be given to having a ≈3 m (10 ft) height.

5
Q

If surge protection is required, the recommended space allocation for cable terminations is _____ times greater than the estimated space for cross connections with no surge protection.

a. Two
b. Two to four
c. Three
d. Three to four

A

b. Two to four

p 3-12

When cabling requires surge protection, the recommended space allocation is two to four times larger than the space above for cross-connections.

6
Q

Space separation, shielding failures, and input/output cabling are all examples of _____ that cause EMI problems.

a. Receiving or receptor elements
b. Transfer or propagation sources
c. Conducted and radiated emission sources

A

b. Transfer or propagation sources

p 2-16

```Transfer or propagation sources, including:
–– Space separation.
–– Shielding failures.
–– Poor filtering.
–– Improper grounding (earthing).
–– Electrical power lines.
–– Input/output cabling.```
7
Q

Measuring the electrical and magnetic field strength of the outgoing radiation determine radiated emissions. One unit of measure for the electrical field strength is:

a. Volts per meter^2
b. Amperes per meter^2
c. Amperes per meter
d. Volts per meter

A

d. Volts per meter

p 2-9

The unit of measure for the electric field strength is volts per meter, millivolts per meter, or microvolts per meter. The use of each depends on the amplitude of the electric field strengths.

8
Q

Runs of unshielded and untwisted conductors in balanced twisted-pair cables are susceptible to external unwanted signal emissions because they can behave as antennas.

a. True
b. False

A

a. True

p 2-7

9
Q

When evaluating the potential for an electromagnetic environment where telecommunications cabling or equipment is to be installed, the maximum acceptable field intensity (measured using an electric field intensity meter) is _____ V/m for general purpose telecommunications equipment and cabling.

a. 1
b. 2
c. 3
d. 5

A

c. 3

p 2-11

Electric field intensity meter—The acceptance criteria is 3 V/m maximum for general purpose telecommunications equipment and cabling. If measured field intensities are above 3 V/m, the appropriate type of shielding should be considered.

10
Q

When measuring EMC, measurements of radiated interference are normally taken over a frequency spectrum of:

a. 30 MHz to 5 GHz
b. 1 MHz to 5 GHz
c. 1 MHz to 30 MHz
d. 100 kHz to 30 MHz
e. 100 kHz to 1 MHz

A

a. 30 MHz to 5 GHz

p 2-9

Measurements of conducted interference are normally taken over a frequency spectrum of 100 kHz to 30 MHz.

Measurements of radiated interference are normally taken over a frequency spectrum of 30 MHz to 5 GHz.

11
Q

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

a. 60 dB or greater
b. 30 dB to 40 dB or greater
c. Less than 30 dB

A

b. 30 dB to 40 dB or greater

p 2-48

It is recommended to use an overall longitudinal balance of 60 dB or greater at low frequencies (e.g., voice) and 30 dB to 40 dB or greater at high frequencies (e.g., 1–300 MHz). For a 40 dB immunity, the unbalance of the voltages in each conductor of the cable pair in regards to the ground plane shall be one percent

12
Q

An EMI problem is always a circuit.

a. True
b. False

A

a. True

p 2-15

A significant part of accomplishing EMC depends on the following considerations:
• All EMI problems are explainable by the basic laws of physics—the EMI problem is always a circuit.

13
Q

To successfully filter both common mode (CM) and differential mode (DM) unwanted signals, the preferred method is:

a. Contact discharge
b. A magnetic scheme
c. Conductor twisting
d. Line coupling

A

b. A magnetic scheme

p 2-24

To successfully filter both types of unwanted signals, a magnetic scheme is preferred. CM unwanted signal reduction is effective when afflicted lines are coupled together through a ferrite bead.

14
Q

Isolation transformers for data signals are quite stringent as they are _____ devices and shall provide isolation within a _____ frequency range.

a. Narrowband; narrow
b. Wideband; wide
c. Wideband; narrow
d. Narrowband; wide

A

b. Wideband; wide

p 2-40

Isolation transformers for data signals are quite stringent as they are wideband devices and shall provide isolation within a wide frequency range. Because of this, these components are high-cost devices and are implemented in the circuit level of data communications electronics
(e.g., LAN equipment).

15
Q

Generally, instrumentation shields should only be grounded at one end.

a. True
b. False

A

a. True

p 2-33

Generally, instrumentation shields should only be grounded at one end. For longer runs and inter-facility runs, cable shields are generally grounded at each end.

16
Q

For telecommunications cabling within joint-use tunnels, to limit unwanted signal currents, the potential difference between the two grounds shall be no more than ___ V rms (volt root mean square) to avoid problems with conductive ground loops.

a. 1.50
b. 1.00
c. 0.75
d. 0.50

A

b. 1.00

p 2-47

The potential difference between the two grounds shall be no more than 1.0 Vrms to avoid problems with conductive ground loops.

17
Q

Power line filters are usually designed to mitigate EMIs in the line for:

a. CM disturbances
b. DM disturbances
c. Both CM and DM disturbances

A

c. Both CM and DM disturbances

p 2-39

Power line filters are usually designed to mitigate EMIs in the line for both CM and DM disturbances as well (Figure 2.12)

18
Q

You are placing Category 6 unshielded twisted-pair (UTP) in cable tray down a hallway past the elevator mechanical room. What action should you take to avoid effects of electromagnetic interference (EMI)?

a. Provide a minimum separation of 1220 mm (48 in)
b. Provide a minimum separation of 2060 mm (81 in)
c. Require the architect to install metallic foil shielding on the mechanical room walls
d. Provide RMC/IMC (rigid metallic conduit/intermediate metal conduit) through all areas within 4.6 m (15 ft) of the mechanical room

A

a. Provide a minimum separation of 1220 mm (48 in)

p 2-28

Minimum separation from Electric motors and transformers ≈1220 mm (48 in)

19
Q

Contact discharges level number X 2 will give you your voltage level.

a. True
b. False

A

a. True

p 2-19 Table 2.3