ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 184

Controller
Computer

EFT Main
Test Unit

Power Interface
Cable

Coupling Clamp

Load/Peripheral

I/O Cables

EUT

Figure 4.28 Setup for assessing the susceptibility of a medical device to electrical fast transients
(EFTs). This test simulates the power line transients that are caused by switching off an inductive
load.

fl fluorescent lamp ballast L5 induce noise at the device under the test's power line input. An

LRC network

fi filters the transients so that they do not fl flow back into the real power line.

Susceptibility to High-Energy Power Line Transients

IEC-61000-4-5 deals with large surges that may directly reach the device's power line
because of lightning. The surge pulses for this test are much wider than those used in EFT
testing. The pulses of IEC-61000-4-5 are tens of microseconds wide, making them able to
induce EMI within the device under test over a 300-kHz bandwidth. Figure 4.30 presents
a typical setup for testing a medical device's susceptibility to high-energy power line
surges. The device under test is placed in the approximate center of a reference ground
plane and is powered and operated in a normal con guration. Throughout the test, the

device under test is observed for indications that a failure has occurred. Transients are
applied to the ac power line leads as well as to I/O lines through coupling/decoupling net-
works. The surge is applied in the common mode (line to ground) at 2 kV. The surge is then
applied in the di

fi

erential mode (line to line) at 1 kV. A series of six positive and six neg-
ative surges are applied with a 1-minute interval between surges.
The impulse generator for these tests uses a 20-

ff

F capacitor charged to the test voltage,
which is discharged through a switch into the device under test via a series coupling capac-
itor and a 40-

µ

resistor placed just after the switch is used for
shaping the test pulse. For line-to-ground testing, the coupling capacitor has a value of
18

Ω resistor. In addition, a 50- Ω

µ F. For line-to-line testing the capacitor is 9 µ F with a 10- Ω resistor added in series. Just

as with the coupling/decoupling networks for EFT testing, a fi filter is placed in series with

the real power line to avoid transients from entering it.