[Diy_efi] Air Flow Meters

Torbjörn Forsman torbjorn.forsman
Wed Mar 8 21:38:18 UTC 2006

A hot wire or hot film AFM can be given just any characteristic the 
engine manufacturer wants. In most cases, a logarithm or sqare root 
characteristic is preferred in order to get better resolution at small 
air flows (idling). The signal from the AFM is normally fed to a 8-bit 
A/D converter in the ECU and if the AFM were linear, the accuracy would 
not be suifficient at idling. In the real world, a system designer must 
also take varying ground potentials, offset errors, temperature drift 
and such parameters into account. Due to all such errors, a higher 
resolution ADC (for example, 10 or 12 bit) maybe does not give much 
better overall resolution in an automotive environment.

Best regards

Torbj?rn Forsman

TheEthereal at gmx.net wrote:
> I'm not sure about hotwire AFMs, but IIRC they're linear. 
>>--- Urspr?ngliche Nachricht ---
>>Von: ScottyGrover at aol.com
>>An: diy_efi at diy-efi.org
>>Betreff: [Diy_efi] Air Flow Meters
>>Datum: Tue, 7 Mar 2006 19:21:59 EST
>>Can anyone tell me about an Air Flow Meter that is linear in voltage with 
>>regard to Air Flow? My unit is an old flap-type Bosch that is logarithmic
>>any log-to-linear conversion circuits that I have found are in the
>>class where this Bosch unit reads from 2.7 to 8.4 volts.  
>>Thanks in advance, 

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