Campbell Scientific 227-L Delmhorst Cylindrical Soil Moisture Block - Manual (Page 18)

227 Delmhorst Cylindrical Soil Moisture Block
TABLE 7-5. Polynomial Error - 10 Bar Range
BARS
V
s
/ V
x
R
s
(kohms × 0.1)
BARS
COMPUTED
ERROR
0.1 0.0566 0.006 0.1949 0.0949
0.2 0.115 0.013 0.2368 0.0368
0.3 0.2063 0.026 0.3126 0.0126
0.4 0.2701 0.037 0.3746 –0.0254
0.5 0.3506 0.054 0.4670 –0.0330
0.6 0.4286 0.075 0.5756 –0.0244
0.7 0.4624 0.086 0.6302 –0.0698
0.8 0.5238 0.11 0.7442 –0.0558
0.9 0.5833 0.14 0.8778 –0.0222
1.0 0.6296 0.17 1.0025 0.0025
1.5 0.7727 0.34 1.5970 0.0970
1.8 0.8000 0.40 1.7834 –0.0166
2 0.8333 0.50 2.0945 0.0945
3 0.8780 0.72 2.8834 –0.1166
6 0.9259 1.25 6.0329 0.0329
10 0.9444 1.70 9.9928 –0.0072
NOTE: ERROR (BARS) = TABLE 7-3 VALUES – COMPUTED
7.2.4 Programming Examples
7.2.4.1 Example CR1000 Program
This example program is written for a CR1000. Programming for other
CRBasic dataloggers is similar. The 227 sensor is measured with the BrHalf()
instruction. An expression uses the result of the BrHalf instruction (V
s
/ V
x
) to
generate R
s
in kohms. If R
s
is less than 17 kohms, soil water potential is
generated using the polynomial. If R
s
is greater than 17 kohms, 1000 is stored
in the variable.
TABLE 7-6. Wiring for CR1000 Example Program
Color Function CR1000
Black Voltage Excitation VX1 or EX1
Red Signal SE1
White Signal Ground
Clear Shield
12