Campbell Scientific CR7 Measurement and Control System User Manual
Page 85
SECTION 8. PROCESSING AND PROGRAM CONTROL EXAMPLES
8-3
Every 15 minutes, the total rain is sent to Input
Storage. If the total is greater than 0, output is
redirected to Final Storage, the time is output,
and the total is sampled.
Input Location Labels:
1:Rain (mm)
2:15min tot
*
1
Table 1 Programs
01:
60
Sec. Execution Interval
01:
P3
Pulse
01:
1
Rep
02:
3
IN Card
03:
1
Pulse Input Chan
04:
2
Switch closure
05:
1
Loc [:Rain (mm)]
06:
.254
Mult
07:
0
Offset
02:
P92
If time is
01:
0
minutes into a
02:
15
minute interval
03:
10
Set high Flag 0 (output)
03:
P80
Set Active Storage Area
01:
3
Input Storage Area
02:
2
Array ID or location
04:
P72
Totalize
01:
1
Rep
02:
1
Loc Rain (mm)
05:
P89
If X<=>F
01:
2
X Loc
02:
3
>=
03:
0
F
04:
30
Then Do
06:
P80
Set Active Storage Area
01:
1
Final Storage Area
02:
25
Array ID or location
07:
P77
Real Time
01:
220
Day,Hour-Minute
08:
P70
Sample
01:
1
Rep
02:
2
Loc
09:
P95
End
8.3 SUB 1 MINUTE OUTPUT INTERVAL
SYNCHED TO REAL TIME
Instruction 92 has one minute resolution. If
processed output is required on an interval less
than one minute, Instructions 18 and 89 can be
used to set the Output Flag on a shorter
interval.
Instruction 18 takes time (tenths of seconds into
minute, minutes into day, or hours into year),
performs a modulo divide by a user specified
value and loads it into an input location.
When the modulo divisor divides evenly into the
interval, one gets a counter in an input location
that goes to 0 on a periodic interval. In this
example, tenths of seconds into the minute is
modulo divided by 300. The counter counts up
to 295 then goes to 0 (i.e., every 30 seconds;
tenths of seconds into minute has a resolution
of 0.1 seconds).
Instruction 89 is used to set the Output Flag
when the tenths of seconds counter is less than
5 (the execution interval, 0.5 seconds). With
this short program, the Output Flag could be set
when the seconds counter equaled 0.
However, if Instruction 18 followed a series of
instructions that took longer than 0.1 seconds to
execute or was in Table 2, executed at the
same interval as an extensive Table 1, the time
at which Instruction 18 was executed might be
0.1 seconds or more beyond the modulo divisor.
The value output would not equal 0. Setting the
Output Flag when the seconds counter is less
than the execution interval avoids this problem.
Using Instruction 18 keeps the output interval
synchronized with real time. If a counter
incremented within the program was used to
determine when to set the Output Flag, output
would depend on the number of times the table
was executed. The actual time of output would
depend on when the program was actually
compiled and started running. If the table
overran its execution interval (Section 1.1.1),
the output interval would not be the count
multiplied by the execution interval, but some
longer interval.
In this example a temperature (type E
thermocouple) is measured every 0.5 seconds
and the average output every 30 seconds.