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A.
APPENDIX
A.1
HANDLING EMC
A.1.1
Effects of EMI noise and countermeasures
(1)
Symptoms
Some of the symptoms of EMI noise are listed below:
1. Noise occurs on the screen of an ultrasound system being used near the CT system.
2. Waveforms obtained by ECG equipment used near the CT system are irregular.
3. Noise which causes flickering on CRTs used near the CT system.
4. An abnormal image or a communication error may occur if an electric scalpel or a
microwave unit is used.
(2)
Causes
The X-ray unit of the CT system includes a large capacity inverter unit. When this inverter
unit operates, EMI noise in the MHz range level conforms to the IEC 60601-1-2 standards,
some system combinations may generate noise problems.
In particular, when an ultrasound system is used in the vincinity of a CT system, the former
is easily affected by noise produced by the latter.
Possible routes of transmission of EMI noise are listed below.
1. EMI noise is radiated from the CT system, CT cables, etc. to the air in the form of the
electric wave and enters the ultrasound system via the ultrasound system cable or
some other unit connected with the ultrasound system which plays the role of an
antenna. (This is called radiation noise.)
2. EMI noise transmits through a CT system cable, transfers to an ultrasound system
cable, and enters the ultrasound system through this cable. (This is called conduction
noise.)
The routes of noise entry described above may often exist simultaneously.
(3)
Countermeasures
There are two main approaches to counter this problem; the prevention of noise
generation in the system generating the noise, and the prevention of noise entry into the
system affected by the noise. Both approaches must be investigated as countermeasures.
Actual countermeasures are described below for the example of an ultrasound system,
electric scalpel, and a microwave unit used in combination with a CT system.
62
No. 2A201-519EN*A
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