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Ian Williams

Dec 2, 2014

isolation

digital isolators

surge
test

electromagnetic
testing

emc
protection

precision DAC

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Related

Part III: Get CerTIfied, not certi-FRIED! Electromagnetic
compatibility testing explained

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Welcome to part three of this blog series discussing electromagnetic
compatibility (EMC) testing. In parts one and two we discussed the background of certification testing and
the specifications for ESD and radiated EMI immunity tests. This time, we’ll
continue with the details of electrical fast transient (EFT) and surge
testing.

IEC 61000-4-4: EFT (Electrical Fast
Transients)

EFT events occur as a result of arcing contacts in switches and
relays. Industrial environments leveraging electromechanical switches to connect
and disconnect inductive loads may experience these issues frequently. IEC
61000-4-4 specifies the EFT threat in both power and data lines.

Table 1: IEC 61000-4-4
threat levels and test voltages

Power Supply Port

I/O, Signal, Data and Control Lines

Threat Level

Open-Circuit Voltage (kV)

Short-Circuit Current (A)

Open-Circuit Voltage (kV)

Short-Circuit Current (A)

1

0.5

10

0.25

5

2

1

20

0.5

10

3

2

40

1

20

4

4

80

2

40

The EFT waveform is described in terms of a voltage across a 50
Ω load from a generator having a nominal dynamic source impedance of 50 Ω. The
output occurs as a burst of high voltage spikes at a repetition rate ranging
from 2 kHz to 5 kHz. The burst length is defined as 15 ms with bursts repeated
every 300 ms. Each individual burst pulse has a rise time of 5 ns and a total
duration of 50 ns.

Figure 1: IEC 61000-4-4 EFT voltage
waveform

During the EFT test, the engineer connects the device under test
to a power supply with 3 m of cable and places it on a small wooden platform.
Part of the cable passes through a special trough with wooden side panels and a
triangular metallic inner chamber. The EFT generator is connected to the
metallic chamber of the trough and the test waveform is applied. The EFT
waveform can then couple to the device under test’s power supply cable.

Figure 2: IEC 61000-4-4 EFT test hardware
setup

IEC 61000-4-5: Surge

Lightning strikes and switching cause the most severe transient
conditions on power and data lines. Switching transients include power system
switching, load changesand short circuit faults. Lightning transients may result
from a direct strike or induced voltages and currents due to an indirect
strike.

The IEC 61000-4-5 standard defines a transient entry point and a
set of installation conditions. The transient is defined in terms of a generator
producing a given waveform and having a specified open circuit voltage and
source impedance. Two surge waveforms are specified: the 1.2 x 50 µs
open-circuit voltage waveform and the 8 x 20 µs short-circuit current
waveform.

Figure 3: IEC 61000-4-5 surge
waveforms

Table 2: IEC 61000-4-5 threat
levels and test voltages

Threat Level

Power Supply

Unsym Lines (Long Distance Bus)

Sym Lines

Data Bus (Short Distance)

Coupling Mode

Coupling Mode

Coupling Mode

Coupling Mode

Line-Line

ZS = 2Ω

Line-GND

ZS = 12Ω

Line-Line

ZS = 42Ω

Line-GND

ZS = 42Ω

Line-GND

ZS = 42Ω

Line-GND ZS = 42Ω

1

Voltage

n/a

0.5 kV

n/a

0.5 kV

1 kV

n/a

Current

n/a

42 A

n/a

12 A

24 A

n/a

2

Voltage

0.5 kV

1 kV

0.5 kV

1 kV

1 kV

0.5 kV

Current

250 A

83 A

12 A

24 A

24 A

12 A

3

Voltage

1 kV

2 kV

1 kV

2 kV

2 kV

n/a

Current

500 A

167 A

24 A

48 A

48 A

n/a

4

Voltage

2 kV

4 kV

2 kV

4 kV

n/a

n/a

Current

1 kA

333 A

48 A

95 A

n/a

n/a

5

Voltage

Varies

Varies

2 kV

4 kV

4 kV

n/a

Current

Varies

Varies

48 A

95 A

95 A

n/a

Waveforms

Voltage

1.2 x 50
µs

1.2 x 50
µs

1.2 x 50
µs

1.2 x 50
µs

1.2 x 50
µs

1.2 x 50
µs

Current

8 x 20 µs

8 x 20 µs

8 x 20 µs

8 x 20 µs

8 x 20 µs

8 x 20
µs

For the surge test, the engineer places the device under test on
a small wooden platform and connects to its power supply through a heavy-duty LC
filter network. The surge generator is connected to the capacitors of the LC
filter, allowing the device under test to be exposed to surge conditions while
protecting the power supply.

The surge voltage is tested at both positive and negative
polarities. Connections are made using all possible combinations across the
device under test’s power supply terminals, both differentially and
common-mode.

For the surge test, the engineer places the device under test on
a small wooden platform and connects to its power supply through a heavy-duty LC
filter network. The surge generator is connected to the capacitors of the LC
filter, allowing the device under test to be exposed to surge conditions while
protecting the power supply.

The surge voltage is tested at both positive and negative
polarities. Connections are made using all possible combinations across the
device under test’s power supply terminals, both differentially and
common-mode.

Figure 4: IEC 61000-4-5 surge test hardware
setup

Stay tuned for the final installment in the series, where we’ll finish
discussing the most common tests and recap what we’ve learned.

Related
resources:

Bridge Sensor Signal
Conditioner with Current Loop Output, EMC Protection reference design

Two-Channel
Source/Sink Combined Voltage & Current Output, Isolated, EMC/EMI Tested
reference design

Part I – Get CerTIfied, not certi-FRIED! Electromagnetic
compatibility testing explained.

Part II – Get CerTIfied, not certi-FRIED! Electromagnetic
compatibility testing explained.

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