Campbell Scientific CR7 Measurement and Control System User Manual
Page 112
SECTION 10. PROCESSING INSTRUCTIONS
10-10
NT is the total number of input samples
processed in the Output Interval
INTERMEDIATE STORAGE REQUIREMENTS
The number of Intermediate locations will
depend upon the number of input values and
outputs desired:
1.
Define K as the number of input values.
2.
Define S as the maximum of either the
variances, standard deviations, or C, where
C = K if K < the number of correlations
requested, or
C = number of correlations + 1 if K > the
number of correlations requested.
3.
Define Q as the maximum of either the
covariances or correlations desired.
4.
Define P as the total number of outputs
desired.
The amount of intermediate memory locations
(IML) required, is then given by:
IML = K + S + Q + P + 2
EXECUTION TIME
If K, S, and Q are defined as in the previous
section, the execution time of the CV/CR
Instruction in milliseconds can be approximated
by:
T(ms) = 1.1K + 0.5S + 0.9Q + 1.8
When evaluating how frequently input samples
can be processed by the CV/CR Instruction
(i.e., determining the minimum program table
execution interval), the time required to make
the measurements and order the input values
must be added to the CV/CR execution time.
Two alternatives exist for the measurement
portion of the programming. The fastest
method is to group as many sensors as
possible into the fewest measurement
instructions, ignoring the Input location order
required by the CV/CR Instruction. After the
measurements are made, use "move"
instructions (i.e., 31 and 54) to obtain the proper
input order. The slower alternative is to order
separate measurement instructions directly as
required by the CV/CR Instruction. While
avoiding "move" instructions, this approach
uses more measurement instructions. The
reason the first method is in general faster is
that less overhead time is required in going
from one measurement to another within a
single instruction (using the "repetitions"
feature) than in going from one measurement
instruction to another.
In many situations, the CR7 must perform
measurement and processing tasks in addition
to those associated with the CV/CR Instruction.
Uninterrupted operation of the CV/CR
Instruction is assured by entering it in Program
Table 1 (highest priority) and placing the
additional tasks in Program Table 2.
A covariance correlation example is given in
Section 8.
*** 66 ARCTAN ***
FUNCTION
Calculate the angle in degrees whose tangent is
X/Y. The polarity of X and Y must be known to
determine the quadrant of the angle, as shown
here. If 0 is entered for Parameter 2, the
Arctangent of X is the result (limits of the
function are -90o < ARCTAN < 90o).
Quadrant
Sign of X
Sign of Y
I
+
+
II
+
-
III
-
IV
+
PAR. DATA
NO.
TYPE
DESCRIPTION
01:
4
Input location of X
[X]
02:
4
Input location of Y
[Y]
03:
4
Destination input location for
ARCTAN(X/Y)
Input locations altered: 1
*** 68 EXTENDED PARAMETERS 4 DIGIT ***
FUNCTION
This instruction is used to give other instructions
additional parameters. Each of the eight
parameters in Instruction 68 is defined by the
instruction it follows. Refer to the specific
instruction that uses extended parameters.
Input location altered: 0