last updated 1/7/99
Here's the formula used:
StdAirDensity = 1.22556 and is defined at 59.0F degrees, 0.0% humidity, and 29.92
inches on the barometer
Temp_c = (Temp-32.0) * 5.0 / 9.0;
Temp_k = Temp_c + 273.0;
Baro_mb = Barometer / (29.92 / 1013.0);
Baro_pa = Baro_mb * 100.0;
SaturationPressure_mb = 6.11 * pow(10,(7.5*Temp_c)/(237.7+Temp_c));
VaporPressure_mb = Humidity * SaturationPressure_mb / 100.0;
TempVirtual_k = Temp_k / (1.0 - (VaporPressure_mb/Baro_mb)*(1.-0.622));
// D = P/(T*R)
AirDensity = Baro_pa / (TempVirtual_k*GasConstant);
% Std Density = AirDensity/StdAirDensity*100
Just so I don't lose the small amount of work I did to program this in my RPN calculator, I have listed my "program" here.
Legend: < (recall), > (store), = (enter), ? (input), -> (covert to)
lbl d
t?
h?
b?
<t
-> degrees celcius
>c (celcius)
273
+
>k (kelvin)
<b
=
29.92
=
1013
/
/
>m (barometer, millibars)
100
x
>p (barometer, pascals)
6.11
=
<c
=
7.5
x
=
<c
=
237.7
+
/
10x (to the 10th power)
x
>s (saturation pressure)
=
<h
x
100
/
>v (vapor pressure)
<k
=
1
=
<v
=
<m
/
=
0.378
x
-
/
>l (virtual temp)
<p
=
<l
=
287
x
/
>d (air density)
1.22556
/
100
x
>e (% std air density)
rtn