7 logarithmic sampling using loops – Campbell Scientific TD Operating System Addendum for CR510, CR10X, and CR23X User Manual
Page 37
TD ADDENDUM—SECTION 8. PROCESSING AND PROGRAM CONTROL EXAMPLES
AD-8-7
10:
P69
Wind Vector
01:
1
Rep
02:
180
Samples per sub-interval
03:
0
Polar Sensor/(S, D1, SD1)
04:
1
Wind Speed/East Loc WS
05:
2
Wind Direction/North Loc WD_360
11:
P71
Average
01:
2
Reps
02:
3
Loc Temp_F
12:
P
End Table 1
8.6 CONVERTING 0-360 WIND DIRECTION
OUTPUT TO 0-540 FOR STRIP CHART
If 0-360 degree wind direction is output to a strip
chart the discontinuity at 0/360 will cause the pen
to jump back and forth full scale when the winds
are varying from the north. In the days of strip
charts this was solved with a 0-540 degree pot on
the wind vane (direction changes from 540 to 180
and from 0 to 360 so the pen only jumps once
when the wind is out of the north or south).
When faced with the necessity of strip chart
output (see previous example), the following
algorithm can be used to change a 0-360
degree input to 0-540. (If you have a 0-540 pot,
it can be used with the CR10 since the Wind
Vector Instruction, 69, will work with this output.)
To change 0-360 degrees to the 0-540 degrees,
360 degrees must sometimes be added to the
reading when it is in the range of 0 to 180. The
following algorithm does this by assuming that if
the previous reading was less than 270, the vane
has shifted through 180 degrees and does not
need to be altered. If the previous 0-540 reading
was greater than 270, 360 degrees is added.
This example is written as a subroutine, used by
the previous example to output an analog
voltage to a strip chart.
Input Location Labels:
2:WD_360
6:WD540_out
10:WD_540
*
3
Table 3 Subroutines
*
3
Table 3 Subroutines
01:
P85
Beginning of Subroutine
01:
1
Subroutine Number
02:
P89
If X<=>F
01:
10
X Loc WD_540
02:
3
>=
03:
270
F
04:
30
Then Do
03:
P86
Do
01:
11
Set high Flag 1
04:
P94
Else
05:
P86
Do
01:
21
Set low Flag 1
06:
P95
End
07:
P31
Z=X
01:
2
X Loc WD_360
02:
10
Z Loc [:WD_540 ]
08:
P89
If X<=>F
01:
10
X Loc WD_540
02:
4
<
03:
180
F
04:
30
Then Do
09:
P91
If Flag/Port
01:
11
Do if flag 1 is high
02:
30
Then Do
10:
P34
Z=X+F
01:
10
X Loc WD_540
02:
360
F
03:
10
Z Loc [:WD_540 ]
11:
P31
Z=X
01:
10
X Loc WD_540
02:
6
Z Loc [:WD540_out]
12:
P95
End
13:
P95
End
14:
P95
End
15:
P
End Table 3
8.7 LOGARITHMIC SAMPLING USING
LOOPS
A ground water pump test requires that water
level be measured and recorded according to
the following schedule.