Campbell Scientific CR23X Micrologger - Manual (Page 35)

1-1
SECTION 1. FUNCTIONAL MODES
1.1 DATALOGGER PROGRAMS - 1 ,
2 , 3 , AND 4 MODES
Data acquisition and processing functions are
controlled by user-entered instructions
contained in program tables. Programming can
be separated into 2 tables, each having its own
user-entered execution interval. A third table is
available for programming subroutines which
may be called by instructions in Tables 1 or 2 or
by special interrupts. The
1 and 2
Modes are used to access Tables 1 and 2. The
3 Mode is used to access Subroutine
Table 3.
The 4 Mode Table is a table of values
used in the program that someone can change
while the rest of the program is protected.
These values may be used for sensor
calibrations or to select optional sensors. The
4 Table is only available when a special
program created by EDLOG is loaded in the
CR23X.
When a program table is first entered, the
display shows the mode (table) number on the
first line and 0000 on the second line. Keying
an "A" will advance the editor to the scan
interval. If there is an existing program in the
table, keying an instruction location number
prior to "A" will advance directly to the
instruction (e.g., 5 will advance to the fifth
instruction in the table).
1.1.1 SCAN (EXECUTION) INTERVAL
The scan interval is entered in units of seconds
as follows:
1/100 .... 1 second, in multiples of 1/100 (.01)
1 ........... 6553.5 seconds, in multiples of 1/10
(0.1)
Execution of the table is repeated at the rate
determined by this entry. The table will not be
executed if 0 is entered.
The sample rate for a CR23X measurement is
the rate at which the measurement instruction
can be executed (i.e., the measurement made,
scaled with the instruction's multiplier and
offset, and the result placed in Input Storage).
Additional processing requires extra time. The
throughput rate is the rate at which a
measurement can be made and the resulting
value stored in Final Storage. The maximum
throughput rate for fast single-ended
measurements, other than burst
measurements, is 600 measurements per
second (24 measurements repeated 25 times
per second with the settling time set at 100
µ
s
with Instruction P132).
If the specified execution interval for a table is
less than the time required to process that
table, the CR23X finishes processing the table
and waits for the next occurrence of the
execution interval before again initiating the
table (i.e., when the execution interval has
elapsed and the table is still executing, that
execution is skipped). Since no advantage is
gained in the rate of execution with this
situation, it should be avoided by specifying an
execution interval adequate for the table
processing time.
NOTE: Whenever the processing time of
the user's program exceeds a table's
execution interval, an error is logged in
memory. The number of overrun errors
can be displayed and reset in the
B
mode (Section 1.6) or using the
Telecommunications A command (Section
5.1). An overrun will also cause “
T
o
” to
appear in the lower right corner of the
display. “
T
o
” will appear on the first table
overruns and continue to be displayed until
table overruns stop and
0 or another
mode command is entered.
In some cases, the processing time may exceed
the execution interval only when the Output Flag is
set and extra time is consumed by final Output
Processing. This may be acceptable. For
example, suppose it is desired to sample some
phenomena every 0.1 seconds and output
processed data every 10 minutes. The processing
time of the table which does this is less than 0.1
seconds except when output occurs (every 10
minutes). With final output the processing time is
1 second. With the execution interval set at 0.1
seconds, and a one second lag between samples
once every 10 minutes, 9 measurements out of
5000 (.18%) are missed: an acceptable statistical
error for most populations.