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EMI, EMC, tests

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Old October 16th 04, 02:54 PM
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Default EMI, EMC, tests

can someone briefly show the difference between EMI, EMC tests?

Old October 17th 04, 09:42 AM
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In message , Fritz
can someone briefly show the difference between EMI, EMC tests?

Simple definitions:
ElectroMagnetic Interference (EMI) = How much (quantity) EMI does the
item under test generate.

ElectroMagnetic Compatibility (EMC) = How susceptible to interference is
the item under test.

Example 1:
A radio transmitter may have good EMC properties (i.e. It is not
generally susceptible to interference from other sources) but it
generates a lot of EMI - radio waves; (but that's what it is meant to
do). OK, this is a bit of a special case.

Example 2:
A GPS receiver is listening for very low level radio signals disguised
as noise. It needs to have good EMC properties (i.e. it is not very
susceptible) to allow it to work as intended. It might generate (from
its own internal circuits) some small amount of EMI which could effect
itself or other equipment nearby. Hence most EMC tests have a distance
in the test results, the "safe distance" it can be placed next to
another item.

This "safe distance" can be difficult to understand. However, if you
look at the compass and note the reading, then put your headset next to
the compass it will give a different reading. Now slowly move the
headset away from the compass until the compass reading is back to
normal. Measure the distance from the headset to the compass and you
have the "compass safe" distance for that particular headset/compass
combination. This is the magnetic wave safe distance. In electronics,
we use electromagnetic waves (generated by electricity, not natural
magnetic waves), but the same principle applies.

Hope that helps

Old October 20th 04, 11:00 PM
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Alan wrote:

Hope that helps



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