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Electromagnetic compatibility (EMC).

Extracts from this document...

Introduction

Ravinder kalirai

Visit report

The visit consisted of a trip to Land Rover in gaydon. We visited 3 areas, EMC (electromagnetic compatibility), optical engine lab and the semi anechoic chamber.

Each area is concern to meet the various demands of their customers and the law.

Electromagnetic compatibility (EMC)

Electromagnetic compatibility, the ability of a device, equipment or systems to function satisfactory in its electromagnetic environment without introducing intolerable electromagnetic disturbance to anything in that environment.

Before distributions to customers, every electrical device that is manufactured must pass some test in order to prevent the interference given to the environment as well as to prevent the interference caused by the environment.

The big advantage of anechoic chambers for emission measurements are that the facility is indoor, and thus unaffected by the weather and the ambient noise level is very low and does not need to measured every day, disadvantage that such facility are their huge cost.

Optical engine lab

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Middle

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Using special test vehicles to carries out exterior noise measurements, which makes it possible to study the contribution of each sound source like engine, exhaust, air-intake and tires noise. For theses investigations to take place they are equipped with a semi anechoic chamber.

The semi anechoic chamber provides and environment where there is no reflection from the walls. This means that the semi anechoic chamber does not affect the sound given off by the car.

In the semi anechoic chamber for the test to be carried out the complete vehicle is either tested at rest or in driving conditions on a roller test bench. On a roller test bench cars can then be driven in multitudes of ways- hard acceleration, cruise or deceleration etc- while banks of microphones positioned on both sides of chambers which are 2.5m

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Conclusion

It is similar to the anechoic chamber. It has wedges on the walls and the ceiling but not on the floor. The wedges are to absorb sound and prevent any reflection of sound.

The wedges are around 1.83m, this would provide quite good absorption of sound waves but for effective absorption the wedge should be around 2.83m.

Foam absorbers / λ of absorbers

                            2

Speed of sound = 40m/s

For effective absorbers:

V=f λ  

340 = 60

= 5.67m   = 2.83m

       2

Wedges to be made 2.83m would be to big and to expensive.

Using slick tires eliminates tires noise. There are no treads therefore no0 compressions of air in the treads.

The sound absorbing perforated metal wedges offer practical advantages over those made from conventional fiberglass or foam - these include impact / fire-resistance, cleanablility, light reflection, repaintability and durability.

image02.jpg

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