Weather Corrections

[Greg Hermann]

>> OK, we have on some applications, Baro, and IAT/MAT.  During
>> crank, we can sample for airtemp, and Baro.  As I recall there is
>> a formula for working out humidity from that.  Is that "correction"
>> used somewhere, in the gm ecms?.  They have some tables for
>> baro, and temp, so would it be safe to assume that the humidity
>> is worked into the corrections somewhere?.
>You also need a wet bulb, vapor pressure and ferrel equations to
>calculate humidity.  This is a rather long computation, I can
>post the formulas if needed.  I do not think it is safe to say that
>humidity is in equations, as I do not know of any cars that have
>wet bulb pyschrometers.  Some Diamler-Chrysler cars use a
>humidity sensor for interior climate control.
>alex
>
You might be able to get close to calculating humidity with IAT, TPS, a
really good MAF sensor, MAP, and an idea as to the engine's VE
characteristics, since air density varies with relative humidity--but I
seriously doubt that anybody is doing this. A humidity sensor, accurate to
plus or minus 2%, for commercial HVAC apps costs about $200.

Regards, Greg