MAP map or MAF map

Mike Wesley - SLIP mwesley at
Mon May 1 12:09:23 GMT 1995

On Wed, 26 Apr 1995, Garrett McWilliams wrote:

> Steve wrote:
> >The upstream temp sensor in the hot wire sensor isn't there to measure
> >the actual temperature of the incoming air but to determine the change
> >in temperature between the heating element and the detection element.
> >A simplified mass flow meter would consist of two sensors, one upstream
> >and one downstream of the heating element. You would expect the down
> >stream element to be warmer than the upstream one because of the (heat
> >carrying) mass going in that direction. 
> >So the difference in heating at the sensor is proportional to the mass
> >flow rate.
> >
> I had thought the MAF sensor measured how much current it took to keep
> the heated wire at a constant temperature, i.e. more air going through cools
> it off more -> more current to maintain temp of the wire.  Is this also used
> or am I way off base?
> Garrett McWilliams
Absolutely correct!

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