Operator`s manual

SECTION 2. INTERNAL DATA STORAGE
2-3
The resolution of the low resolution format is
reduced to 3 significant digits when the first (left
most) digit is 7 or greater (Table 2.2-2). 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
foot, the level must be less than 70 feet for low
resolution output to display the 0.01 foot
increment. If the water level is expected to
range from 50 to 80 feet the data could either be
output in high resolution or could be offset by 20
feet. (transforming the range to 30 to 60 feet.).
TABLE 2.2-2. Decimal Location in Low
Resolution Format
Absolute Value Decimal Location
0 - 6.999 X.XXX
7 - 69.99 XX.XX
70 - 699.9 XXX.X
700 - 6999. XXXX.
While output data have the limits described
above, the computations performed in the 21X
are done in floating point arithmetic. Values are
rounded when converting to Final Storage
Format.
2.2.2 INPUT AND INTERMEDIATE STORAGE
DATA FORMAT
In Input and Intermediate Storage, 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
the description of the J and K
telecommunications commands in Appendix C.
2.3 DISPLAYING STORED DATA ON
KEYBOARD/DISPLAY - *7 MODE
The *7 Mode is used to display Final Storage
data. Enter the Mode by keying *7. The display
will show "07:XXXXX", where XXXXX is the
Final Storage location (DSP) where the next
data will be stored. Two options are available:
1. Press A to advance and display the
output array ID of the oldest array in
Final Storage.
2. Enter a Final Storage location number.
When A is pressed, the DPTR will jump
to the location entered and, if it is not at
the start of an array, advance to the first
start of array. The display will show the
Array ID.
Repeated use of the A key advances through
the output array, while use of the B key backs
the DPTR through memory.
The Final Storage location of the data point
being viewed may be displayed by keying #. At
this point, another location may be entered,
followed by A to jump to the start of the output
array equal to or just ahead of the location
entered. Whenever a location number is
displayed by keying #, the corresponding data
point can be displayed by keying C. To advance
to the start of the next output array, key #A. To
back up one output array key #B.
TABLE 2.3-1. *7 Mode Command Summary
Key Action
A Advance to next data point
B Back-up to previous data point
# Display location number of currently
displayed data point value
C Display value of current location
#A Advance to start of next output array
#B Back-up to previous output array