Specifications

Section 8. Processing and Math Instructions
8-29
SatVP (Dest, Temp)
Calculates saturation vapor pressure over water (Svpw) in kilopascals from the
air temperature (°C) and places it in the destination variable. The algorithm for
obtaining Svpw from air temperature (°C) is taken from: Lowe, Paul R.: 1977,
“An approximating polynomial for computation of saturation vapor pressure,”
J. Appl. Meteor, 16, 100-103.
Saturation vapor pressure over ice (Svpi) in kilopascals for a 0°C to -50°C
range can be obtained using SatVP and the relationship
Svpi = -.00486 + .85471 Svp + .2441 Svp
2
where Svpw is derived by SatVP. This relationship was derived by Campbell
Scientific from the equations for the Svpw and the Svpi given in Lowe’s paper.
Parameter
& Data Type
Enter
Dest
Variable in which to store saturation vapor pressure (kPa).
Temp
Variable containing air temperature (°C).
Example: The following program uses the SatVP instruction to derive
saturation vapor pressure, in kilopascals, from a temperature measurement in
the program.
Dim XY(2),Polar(2),Deg,AnglDeg
Public Temp, SatVPkPa
DataTable (EnvData,1,-1)
DataInterval (0,1,Min,10)
Sample (1,Temp,FP2)
Sample (1,SatVPkPa,FP2)
EndTable
BeginProg
Scan (1,Sec,3,0)
VoltSE(Temp,1,mV5000,2,0,0,_60Hz,0.1,-40.0)
SatVP (SatVPkPa,Temp)
CallTable EnvData
NextScan
EndProg
SGN (Number)
Used to find the sign value of a number.
Syntax
x = SGN (Number)
Remarks
Returns an integer indicating the sign of a number.
The argument number can be any valid numeric expression. Its sign
determines the value returned by the Sgn function:
If X > 0, then Sgn(X) = 1.