MAP map or MAF map

Steve Baldwin steveb at kcbbs.gen.nz
Thu Apr 27 08:31:07 GMT 1995


> 
> 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?
> 

Not at all. What I described was the 'original' hot wire anenometer. The
next extension of the principle goes something like ....'Hmmmm. I can
generate the heat by passing a current through a resistive wire. I can
also measure the temperature of the wire by measuring its resistance.
Therefore heater and sensor can be the same wire. So why can't I heat
the wire and measure the current needed to maintain a steady
temperature/resistance. QED. <Insert Douglas Adams quote here>'
This is the hot wire anenometer. The thin film version is closer to the
original layout.

Steve.



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