ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 181

SW 1

WIDEBAND EMI

+ 12V

TV Flyback with voltage multiplier

SW SPST

+ C 1
1000uF

Integrated Tripler

primary a

T1

*= Heatsink

*

Q1
2 N305 5

R1
1K

TEM Horn

D1
1N4007

primary b

+15KV

L1

feedback

SG1

R2

SPARK
GAP

Z2

110 Ohm 2W

*

Z1

Q2
2N3055

D1
1N4007

Blumlein Pulse Generator

Figure 4.24 In this experimental wideband generator, a push-pull oscillator drives a TV flyback to produce 15 to 20 kV dc. This high volt-
age is used to charge two transmission line capacitors, Z1 and Z2, which are etched on a double-sided PCB.

energy is injected. The frequency range for immunity tests is 150 kHz to 80 MHz, and the
injected RF has an amplitude of 3 V. Figure 4.26 shows a typical test setup. The device
under test is placed in the approximate center and 10 cm above a reference ground plane,
and is powered and operated in a normal con guration. Injection of RF into the ac power

leads is performed with the coupling network shown in Figure 4.27. Testing of signal input
leads is performed via a current clamp on the leads.

fi

Susceptibility to Fast Power Line Transients

IEC-61000-4-4 deals with the immunity that devices must present against repetitive fast
transients that may be induced, for example, by inductive disconnects on the power line cir-
cuit from which the medical device is powered. Electrical fast transients (EFTs) are caused
any time that gaseous discharge occurs (a spark in air or other gas), the most common being
the opening of a switch through which current is

fl flowing. As the switch is opened, arcing

occurs between the contacts: first at low voltage and high frequency while contacts are close

together, and later at a higher voltage and lower frequency as the contacts separate.
Figure 4.28 shows the experimental setup to test for susceptibility to EFT. The device
under test is placed in the approximate center of a reference ground plane and is powered
and operated under worst-case conditions. Throughout the test, the device under test is
observed for any indications of erratic operation. Transients are applied to the power leads
through the use of a coupling/decoupling network. In this network, 33-nF capacitors cou-
ple the high-voltage pulses from the EFT burst generator between ground and the live and
neutral lines of the device under test's power input. The network also includes a

fi

fi filter to

prevent the high-voltage pulses from coupling into the real power line.
The device under test is subjected to 1-kV discharges to the ac power input leads. Each
pulse should reach 900 V by 5 ns 30%

above 500 V. The burst of pulses is delivered with a 5-kHz repetition rate. Both positive
and negative polarity discharges are applied. For each discharge sequence the duration is

30% and should spend no more than 50 ns