Campbell CR9000, Instruction Manual

Page: 98 / 218

Section 6. Data Table Declarations and Output Processing Instructions
6-10
Covariance (NumVals, Source, DataType, DisableVar, NumCov)
Calculates the covariance of values in an array over time. The Covariance of
X
and
Y
is calculated as:
( )
Cov X Y
X Y
n
X Y
n
i i
i
n
i
i
n
i
i
n
( , )
=
⋅
−
⋅
= = =
∑ ∑ ∑
1 1 1
2
where
n
is the number of values processed over the output interval and
X
i
and
Y
i
are the individual values of
X
and
Y
.
Parameter&
Data Type
Enter
Covariance Parameters
NumVals
Constant The number of elements in the array to include in the covariance calculations
Source Variable
Array The variable array that contains the values from which to calculate the covariances. If the
covariance calculations are to start at some element of the array later than the first, be sure
to include the element number in the source (e.g., X(3)).
DataType
A code to select the data storage format.
Constant Alpha Code Numeric Code Data Format
IEEE4 24 IEEE 4 byte floating point
FP2 7 Campbell Scientific 2 byte floating point
DisableVar
Constant,
A non-zero value will disable intermediate processing. When the disable variable is
≠
0 the current
input is not included in the Covariance.
Variable, or Value Result
Expression 0 Process current input
≠
0
Do not process current input
NumCov
Constant The number of covariances to calculate. The maximum number of covariances is
Z/2*(Z+1). Where Z=
NumVals. If X(1) is the first specified element of the source array,
the covariances are calculated and output in the following sequence:
X_Cov(1)…X_Cov(Z/2*(Z+1)) = Cov[X(1),X(1)], Cov[X(1),X(2)], Cov[X(1),X(3)], …
Cov[X(1),X(Z)], Cov[X(2),X(2)], Cov[X(2),X(3)], … Cov[X(2),X(Z)], …
Cov[X(Z),X(Z)]. The first “NumCov” of these possible covariances are output.
FFT (Source, DataType, N, Tau, Units, Option)
The FFT performs a Fast Fourier Transform on a time series of measurements
stored in an array. It can also perform an inverse FFT, generating a time series
from the results of an FFT. Depending on the output option chosen, the output
can be: 0) The real and imaginary parts of the FFT; 1) Amplitude spectrum.
2) Amplitude and Phase Spectrum; 3) Power Spectrum; 4) Power Spectral
Density (PSD); or 5) Inverse FFT.