System Characteristics; Electromagnetic Emissions And Immunity - Philips Avalon FM20 Service Manual

12 Specifications
When electromagnetic interference (EMI) is encountered, for example, if you can hear spurious noises
on the fetal monitor's loudspeaker, attempt to locate the source. Assess the following:
• Is the interference due to misplaced or poorly applied transducers? If so, re-apply transducers
correctly according to directions in this book, or in the Instructions for Use accompanying the
accessory.
• Is the interference intermittent or constant?
• Does the interference occur only in certain locations?
• Does the interference occur only when in close proximity to certain medical electrical equipment?
Once the source is located, there are a number of things that can be done to mitigate the problem:
Eliminating the source. Turn off or move possible sources of EMI to reduce their strength.
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Attenuating the coupling. If the coupling path is through the patient leads, the interference may be
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reduced by moving and/or rearranging the leads. If the coupling is through the power cord,
connecting the system to a different circuit may help.
Adding external attenuators. If EMI becomes an unusually difficult problem, external devices such
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as an isolation transformer or a transient suppressor may be of help. Your service provider can be
of help in determining the need for external devices.
Where it has been established that electromagnetic interference is affecting physiological parameter
measurement values, a physician, or a suitably qualified person authorized by a physician, should
determine if it will negatively impact patient diagnosis or treatment.

System Characteristics

The phenomena discussed above are not unique to this system, but are characteristic of fetal patient
monitoring equipment in use today. This performance is due to very sensitive high gain front end
amplifiers required to process the small physiological signals from the patient. Among the various
monitoring systems already in clinical use, interference from electromagnetic sources is rarely a
problem.

Electromagnetic Emissions and Immunity

The EMC standards state that manufacturers of patient-coupled equipment must specify immunity
levels for their systems. See Tables 1 to 4 for this detailed immunity information. See Table 5 for
recommended minimum separation distances between portable and mobile communications
equipment and the product.
Immunity is defined in the standard as the ability of a system to perform without degradation in the
presence of an electromagnetic disturbance.
Caution should be exercised in comparing immunity levels between different devices. The criteria used
for degradation are not always specified by the standard, and can therefore vary with the manufacturer.
In the table below, the term "device" refers to the Avalon FM20/30/40/50 fetal monitor together with
its accessories. The table gives details of the electromagnetic emissions, and how these are classified,
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