how does air flow sensor work?

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species8350 - 21 Oct 2005 10:52 GMT

Can someone tell me how an air flow sensor works

Part two:

Does it follow that if all the input and output voltages are correct
then the circuit must be fault free?

Thanks

A

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G.T - 21 Oct 2005 12:52 GMT

Hi,

> Can someone tell me how an air flow sensor works

The simplest AFMs (Air Flow Meter) work with a flap into the inlet manifold,
or into the AFM ass'y. The flap's position is determined by the air flow.
This flap is mechanically "linked" to a potentiometer, so the voltage output
is given by a formula like AirFlow=V_airflow.
V_Airflow is given by k*airflow, where k is a constant. I guess that the pot
is usually supplied at 12V, so min airflow = 0 and max airflow=12V. There
may be an offset too, but that's took by the ECU.

More modern AFMs are built with a platinum wire heating a set of resistors.
The resistors are kept at a constant temperature by the heating wire, and
considering the voltage applied to the platinum wire you can deduce the air
flow. There, it's a bit more complex as we're talking about a servo-control,
but come on, electronics engineers are there to achieve that :-)

> Part two:
> Does it follow that if all the input and output voltages are correct
> then the circuit must be fault free?

Yes, IMHO.
Could you tell us a bit more about what you're looking for ? Could you
describe your problem, car type and year ? We've got many knowledgeable
people here which could well help you.

HTH,
G.T
205 Diesel & turbo-Diesel : www.205d.com

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