Campbell Scientific CR7 Measurement and Control System - Manual (Page 17)

CR7 MEASUREMENT AND CONTROL SYSTEM OVERVIEW
OV-7
Table 1.
Execute every x sec.
0.0125 < x < 6553
Instructions are executed
sequentially in the order they
are entered in the table. One
complete pass through the table
is made each execution interval
unless program control
instructions are used to loop or
branch execution.
Normal Order:
MEASURE
PROCESS
CHECK OUTPUT COND.
OUTPUT PROCESSING
Table 2.
Execute every y sec.
0.1 < y < 6553
Table 2 is used if there is a
need to measure and process
data on a separate interval from
that in Table 1.
Table 3.
Subroutines
A subroutine is executed only
when called from Table 1 or 2.
Subroutine Label
Instructions
End
Subroutine Label
Instructions
End
Subroutine Label
Instructions
End
FIGURE OV2-2. Program and Subroutine Tables
OV2.3.1 THE EXECUTION INTERVAL
The execution interval specifies how often the
program in the table is executed, which is
usually determined by how often the sensors
are to be measured. Unless two different
measurement rates are needed, use only one
table. A program table is executed sequentially
starting with the first instruction in the table and
proceeding to the end of the table.
Each instruction in the table requires a finite
time to execute. If the execution interval is less
than the time required to process the table, the
CR7 overruns the execution interval, finishes
processing the table and waits for the next
execution interval before initiating the table.
When an overrun occurs, decimal points are
shown on either side of the G on the display in
the LOG mode (*0). Overruns and table priority
are discussed in Section 1.1.
OV2.3.2 THE OUTPUT INTERVAL
The interval at which output occurs is
independent from the execution interval, other
than the fact that it must occur when the table is
executed (i.e., a table cannot have a 10 minute
execution interval and output every 15 minutes).
A single program table can have many different
output intervals and conditions, each with a unique
data set (output array). Program Control
Instructions are used to set the Output Flag which
determines when output occurs. The Output
Processing Instructions which follow the instruction
setting the Output Flag determine the data output
and its sequence. Each additional output array is
created by another Program Control Instruction
setting the Output Flag high in response to an
output condition, followed by Output Processing
Instructions defining the data set to output.
OV3. PROGRAMMING THE CR7
A program is created by keying it directly into
the datalogger or on a PC using the PC208 or
PC208W Datalogger Support Software program
EDLOG. This manual describes direct
interaction with the CR7. Work through the
direct programming examples in this overview
before using EDLOG and you will have the
basics of CR7 operation as well as an
appreciation for the help provided by the
software. Section OV3.5 describes options for
loading the program into the CR7.