**HP Prime and TI-84+: Saturation Vapor Pressure, Dew Point, Density Altitude (US Units)**

The Program AIRUS
uses US units as the inputs and outputs:

Input:

T = Temperature
in Fahrenheit (°F)

B = Air
Pressure in inHg (inches of Mercury)

H = Relative
Humidity (%)

You can find
these measurements on various weather websites.
Such websites are Accuweather (www.accuweather.com)
and Weather Underground (www.wunderunderground.com).

Output:

S = Saturated
Water Vapor (psi)

A = Approximate
Actual Density Altitude (DSI) (feet)*

X = Dew Point (°F)

*This is an
approximation of density altitude, is an equivalent elevation where the standard
atmosphere is met. (per ICAO, 29.921
inHg, 59°F, 0% humidity).
Let me stress, the density altitude is an approximation.

A list
consisting of temperature, air pressure, relative humidity, saturated water
vapor, approximate DSI, and dew point is also returned to the home screen.

**Equations Used:**

Convert
Temperature from Fahrenheit to Celsius:

C = (T-32)*5/9

Saturation
Vapor Pressure (psi):

S=(610.78*10^((7.5*C)/(C+237.3)))/
6894.757292318

Dew Point (°C):

W=237.3*V/(1-V)
where:

V=(LN(H/100)+((17.27*C)/(237.3+C)))/17.27

Convert from
Celsius to Fahrenheit:

X = W*9/5 + 32

Density
Altitude (feet):

A=145442.1563*(1-((17.326*B)/(1.8*Z))^.235)
where:

Z=(C+273.15)/(1-.378*Y/(33.8639*B))

Y=6.1078*10^((7.5*W)/(237.3+W))

**HP Prime: AIRUS**

EXPORT AIRUS()

BEGIN

// 2015-02-28 EWS

// U.S. Units

LOCAL t,b,h;

LOCAL c,s,d,p,a,v,w;

LOCAL x,y,z;

// Data

INPUT({t,b,h},

"Weather
Data",

{"t
:","b :","h :"},

{"Temperature
(°F)",

"Pressure
(inHg)",

"% Relative
Humidity"});

// t to Celcius

c:=(t-32)*5/9;

// Saturation Vapor
Pressure (Pa)

// wikipedia

s:=610.78*ALOG((7.5*c)/(c+237.3));

// to psi

s:=s/6894.757292318;

// Dew Point (°F)

// ag.arizona.edu

v:=(LN(h/100)+((17.27*c)/(237.3+c)))/17.27;

w:=237.3*v/(1-v);

// w to °F

x:=w*9/5+32;

// Density Altitude

// www.srh.noaa.gov

y:=6.1078*ALOG((7.5*w)/(237.3+w));

z:=(c+273.15)/(1-.378*y/(33.8639*b));

a:=145442.1563*(1-((17.326*b)/

(z*1.8))^.235);

// Output

PRINT();

PRINT("Input:");

PRINT(t+"°F,
"+b+"inHg, "+h+"%");

PRINT("Output:");

PRINT("Sat.
Water Vapor (psi): "+s);

PRINT("Approx.
DSA (ft): "+a);

PRINT("Dew
Point (°F): "+x);

RETURN
{t,b,h,s,a,x};

END;

**TI-84+ AIRUS:**

Disp “T: TEMP °F”

Disp “B: PRESSURE
(INHG)”

Disp “H: REL.
HUMIDITY”

Prompt T,B,H

(T-32)*5/9→C

610.78*10^((7.5C)/(C+237.3))→S

S/6894.757292318→S

(ln(H/100)+((17.27C)/(237.3+C)))/17.27→V

237.3V/(1-V)→W

9W/5+32→X

6.1078*10^((7.5W)/(237.3+W))→Y

(C+273.15)/(1-.378Y/(33.8639B))→Z

145442.1563*(1-((17.326B)/(1.8Z))^.235)→A

Disp “SAT. WATER
VAPOR (°F)”

Pause S

Disp “APPROX DSA
(FT)”

Pause A

Disp “DEW POINT (°F)”

Pause X

Disp {T,B,H,S,A,X}

Example:

Input:

T = 68°F

B = 29.94 inHg
(inches of Mercury)

H = 70%

Output:

S = 0.339111794
psi

A = 790.3879774
feet

W = 57.85583006
°F

Sources:

“Density
Altitude” National Weather Resource: Southern Region Headquarters URL: http://www.srh.noaa.gov/images/epz/wxcalc/densityAltitude.pdf Retrieved February 28, 2015

“Density of Air”
and “Density Altitude” Wikipedia.
URL: http://en.wikipedia.org/wiki/Density_of_air
, http://en.wikipedia.org/wiki/Density_altitude
Retrieved February 26, 2015

“Dewpoint
Formulas” University of Arizona. URL: http://ag.arizona.edu/azmet/dewpoint.html Retrieved February 28, 2015

Glover, Thomas
J. “Pocket Ref” 4

^{th}Editiion. Sequoia Publishing, Inc.: Littleton, CO. 2012 Print
This blog is property
of Edward Shore - 2015

## No comments:

## Post a Comment