Campbell Scientific CR7 Measurement and Control System - Manual (Page 109)

SECTION 10. PROCESSING INSTRUCTIONS
10-7
Input Storage. The instruction requires the set
of input values to be located contiguously in
Input Storage. The user specifies the location
of the first value and how many total values
exist. The number of input values processed by
each type of calculation (means, variances,
etc.) is independently specified for each type.
The order of the input values determines which
inputs are processed for each type of
calculation.
The instruction does not conform to the CR7's
four instruction types. Data located in Input
Storage is processed, and the results returned
to Input Storage whenever an averaging period
is completed (Parameter 7) or the Output Flag
is set. The instruction controlling the Output
Flag must precede the CV/CR Instruction. The
reason the calculated results are returned to
Input Storage is to allow the user access for
additional processing before storing the values
in Final Storage. Sample Instruction 70 must
be used to transfer final results from Input to
Final Storage.
To accommodate cases where it is desirable to
calculate the statistical quantities over time
periods shorter than the Output Interval, an
averaging period shorter than the Output
Interval may be specified. The final values
obtained at the Output Interval are the properly
weighted average of the values calculated at
the subinterval averaging periods. This feature
allows the recording of statistical data over
longer time periods by removing the effect of
longer period frequencies in the input signals;
i.e., it provides a high pass filter. For example,
assume the variance of an input is desired. It is
determined that the averaging period should not
exceed five minutes due to variation in the
mean over longer time intervals. One approach
is to calculate and record the variance every
five minutes. By specifying the subinterval
averaging period as five minutes and the Output
Interval as one hour, however, the average of
the five minute variances are recorded every
hour. The averaging period is entered as the
number of input samples in Parameter 7 of the
CV/CR Instruction. The number of samples for
a given period is given by:
Number of Samples =
Averaging period in seconds
Table execution interval in seconds
PAR. DATA
NO.
TYPE DESCRIPTION
01: 2 Number of input values located
sequentially in input memory
02: 2 Number of means desired
03: 2 Number of variances desired
04: 2 Number of standard deviations
desired
05: 2 Number of covariances desired
06: 2 Number of correlations desired
07: FP Number of input samples in
averaging period
08: 4 Input storage location of first
value in sequential input string
09: 4 First Input Storage location to
store string of final results
If the specified number of samples in the
averaging period (Parameter 7) exceeds the
actual number of samples occurring in the
Output Interval, the Output Interval becomes the
averaging period.