Campbell Scientific CR9000X Measurement and Control System - Manual (Page 211)

Section 6. Data Table Declarations and Output Processing Instructions
Moment
The Moment instruction is used to output the mathematical moment of a value
over the output interval. Orders 2 through 5 are supported by this instruction.
Syntax
Moment( Reps, Source, Order, DataType, DisableVar )
Parameter Enter MOMENT PARAMETERS
Reps
Constant Number of values for which to calculate a moment. If the Reps parameter is greater than 1, an array must
be specified for Source or a Variable Out of Bounds error will be returned when program is compiled.
Source (Var) Name of the variable for which a moment should be saved.
Order The Order parameter is the order of polynomial to be used when calculating the moment.
Constant or Order Description
Variable 2 sum over i (x(i) - Mean)^2 .This moment may also be used to calculate the variance
3 sum over i (x(i) - Mean)^3. This moment may also be used to calculate the skewness
4 sum over i (x(i) - Mean)^4. This moment may also be used to calculate the kurtosis
5 sum over i (x(i) - Mean)^5. This moment may also be used to calculate Univariate and
Multivariate Non-normal Distributions
DataType
Constant The DataType parameter is used to select the format in which to save the data.
DisableVar
Const, Var, Exp
Used to determine whether the current measurement is included in the output saved to the DataTable. 0 =
Process current measurement; non-zero = Do not process current measurement.
RainFlow (Source, DataType, DisableVar, MeanBins, AmpBins, LowerLimit,
UpperLimit, MinAmp, Form)
Processes data with the Rainflow counting algorithm, essential to estimating
cumulative damage fatigue to components undergoing stress/strain cycles. The
algorithm is based on the work done by Stephen Downing and Darrell Socie,
which is documented in Volume 4 Issue 1 of the International Journal of
Fatigue (Jan 1982).
The input signal is processed into either a one or a two dimensional Rainflow
Histogram. The first dimension represents the amplitude of the closed loop
cycle (i.e., the distance between peak and valley); the second, optional,
dimension is the mean of the cycle (i.e., [peak value + valley value]/2). To
perform a 1 dimensional histogram (based solely on the Amplitude of the
cycles), enter 1 for the MeanBins parameter .
The value recorded in each element (bin) of the histogram can either be the
actual number of closed loop cycles that had the amplitude and mean value
associated with that bin, or the ratio of the number of cycles having mean and
amplitude values in the specific bin's range with respect to the total number of
cycles that were counted (i.e. : number of cycles in bin divided by total number
of cycles counted).
The range sizes for the Amplitude Bins are calculated by dividing the
difference between the upper (UpperLim) and lower (LowerLim) limits of the
Mean bins by the number of amplitude ranges (AmpDim).
The MeanBin's range sizes are calculated, similar to the Amp's range size, by
dividing the difference between the upper (UpperLim) and lower (LowerLim)
limit values for the Mean Bins by the number of mean ranges (MeanDim). The
actual range values start at the lower limit (LowLim).
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