Campbell CR23X, Operator'S Manual

Page: 327 / 374

TD ADDENDUM—SECTION 2. INTERNAL DATA STORAGE
AD-2-3
The Timestamp and record number labels are
added automatically.
2.2 DATA OUTPUT FORMAT AND
RANGE LIMITS
Data is stored internally in Campbell Scientific's
Binary Final Storage Format (Appendix C.2).
Data may be sent to Final Storage in either
LOW RESOLUTION or HIGH RESOLUTION
format.
2.2.1 RESOLUTION AND RANGE LIMITS
Low resolution data is a 2 byte format with 4
significant digits and a maximum magnitude of
+7999. High resolution data is a 4 byte format
(see Section 2.2.2).
TABLE 2.2-1. Resolution Range Limits of
CR10 Data
Minimum Maximum
Resolution Zero Magnitude Magnitude
Low 0.000 + 0.001 +7999.
High 0.0000 1x10
-19
+9x10
+18
The resolution of the low resolution format is
reduced to 3 significant digits when the first (left
most) digit is 8 or greater. Thus, it may be
necessary to use high resolution output or an
offset to maintain the desired resolution of a
measurement. For example, if water level is to
be measured and output to the nearest 0.01 ft.,
the level must be less than 80 ft. for low
resolution output to display the 0.01 ft.
increment. If the water level was expected to
range from 50 to 90 feet the data could either
be output in high resolution or could be offset by
20 ft. (transforming the range to 30 to 60 ft.).
2.2.2 HIGH RESOLUTION FINAL STORAGE
DATA, INPUT, AND INTERMEDIATE
STORAGE DATA FORMAT
While low resolution output data have the limits
described above, computations are done in
floating point arithmetic. In high resolution Final
Storage Input and Intermediate Storage, the
numbers are stored and processed in a binary
format with a 23 bit binary mantissa and a 6 bit
binary exponent. The largest and smallest
numbers that can be stored and processed are
9 x 10
18
and 1 x 10-
19
, respectively. The size of
the number determines the resolution of the
arithmetic. A rough approximation of the
resolution is that it is better than 1 in the
seventh digit. For example, the resolution of
97,386,924 is better than 10. The resolution of
0.0086731924 is better than 0.000000001.
A precise calculation of the resolution of a
number may be determined by representing the
number as a mantissa between .5 and 1
multiplied by 2 raised to some integer power.
The resolution is the product of that power of 2
and 2-
24
. For example, representing 478 as
.9336 * 2
9
, the resolution is 2
9
* 2-
24
= 2-
15
=
0.0000305. A description of Campbell
Scientific's floating point format may be found in
Appendix C.
2.3 DISPLAYING STORED DATA ON
KEYBOARD/DISPLAY *7 MODE.
The keyboard display (or the computer in
Keyboard/Display mode) can be used to
examine Data Storage Tables in Final Storage
table data.
Key *7. The display will show: 07:nn where nn
is the number of Data Storage Tables defined.
Enter a table number (followed by the “A” key)
to view that table. Tables are numbered in the
order of the appearance of the Data Storage
Table Instruction (84) in the datalogger
program. Tables in the *1 program area are
numbered first, followed by *2 and those in the
*3 subroutines numbered last.
The display will then show the first field of the
newest record in the table. If the display does
not change, the select table has not had any
data stored in it yet.
When a table is visualized the newest data
record is at the bottom and the oldest is at the
top. When the table is full and a new record is
stored, the records shift up pushing the oldest
record off the top and storing the new record at
the bottom.
The display (or value displayed on the
computer) can be thought of as a cursor, which
can be moved up and down or right and left
through the data. The display shows the field
number to the left of the colon and the data
value to the right. The keys used to move the
display/cursor are summarized in the following
table: