Campbell Scientific CR7 Measurement and Control System - Manual (Page 107)

SECTION 10. PROCESSING INSTRUCTIONS
10-5
PAR. DATA
NO.
TYPE DESCRIPTION
01: 4 Number of values to move
02: 4 1st source location
03: 2 Step of source
04: 4 1st destination location
05: 2 Step of destination
Input locations altered: number of values to
move
*** 55 5TH ORDER POLYNOMIAL ***
FUNCTION
Evaluate a 5th order polynomial of the form.
F(X)=C0+C1X+C2X2+C3X3+C4X4+C5X5
where C0 through C5 are the coefficients for the
argument X raised to the zero through fifth
power, respectively. The magnitude of the user
entered coefficient is limited to a range of
+99999 to -99999. Polynomials with
coefficients outside this range can be modified
by pre-scaling the X value by an appropriate
factor to place the coefficients within the entry
range. Pre-scaling can also be used to modify
coefficients which are very close to 0 in order to
increase the number of significant digits.
PAR. DATA
NO.
TYPE DESCRIPTION
01: 2 Repetitions [REPS]
02: 4 Starting input location for X [X]
03: 4 Dest. input location for F(X)
[F(X) or Z]
04: FP C0 coefficient [C0]
05: FP C1 coefficient [C1]
06: FP C2 coefficient [C2]
07: FP C3 coefficient [C3]
08: FP C4 coefficient [C4]
09: FP C5 coefficient [C5]
Input locations altered: 1 per repetition
*** 56 SATURATION VAPOR PRESSURE ***
FUNCTION
Calculate saturation vapor pressure over water
(SVPW) in kilopascals from the air temperature
(oC) and place it in an input location. The
algorithm for obtaining SVPW from air
temperature (oC) is taken from: Lowe, Paul R.,
1976: 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 oC to -50 oC range can be
obtained using Instruction 55 and the
relationship
SVPI = -.00486 + .85471 X + .2441 X2
where X is the SVPW derived by Instruction 56.
This relationship was derived by Campbell
Scientific from the equations for the SVPW and
the SVPI given in Lowe's paper.
PAR. DATA
NO.
TYPE DESCRIPTION
01: 4 Input location of air temperature
o
C
[TEMP.]
02: 4 Dest. input location for saturated
vapor pressure
[VP or Z]
Input locations altered: 1
*** 57 VAPOR PRESSURE FROM ***
WET-/DRY-BULB TEMPERATURES
FUNCTION
This instruction calculates vapor pressure in
kilopascals from wet- and dry-bulb
temperatures in oC. The algorithm is of the
type used by the National Weather Service:
VP = VPW - A(1 + B*TW)(TA - TW) P
VP = ambient vapor pressure in
kilopascals
VPW = saturation vapor pressure at the wet-
bulb temperature in kilopascals
TW = wet-bulb temperature, deg. C
TA = ambient air temperature, deg. C
P = air pressure in kilopascals
A = 0.000660
B = 0.00115
Although the algorithm requires an air pressure
entry, the daily fluctuations are small enough
that for most applications a fixed entry of the
standard pressure at the site elevation will
suffice. If a pressure sensor is employed, the
current pressure can be used.