Campbell Scientific 253-L and 257-L (Watermark 200) Soil Matric Potential Sensors - Manual (Page 26)

253-L and 257-L Soil Matric Potential Sensors
'CR1000
Public T107_C, kOhms, WP_kPa
Units T107_C=Deg C
Units kOhms=kOhms
Units WP_kPa=kPa
DataTable(Hourly,True,-1)
DataInterval(0,60,Min,10)
Average(1,T107_C,FP2,False)
Sample(1,WP_kPa,FP2)
EndTable
BeginProg
Scan(1,Sec,1,0)
'107 Temperature Sensor measurement T107_C:
Therm107(T107_C,1,1,1,0,_60Hz,1.0,0.0)
'257 Soil matric potential Sensor measurements:
BrHalf(kOhms,1,mV250,2,Vx2,1,250,True,0,250,1,0)
kOhms=kOhms/(1-kOhms)
'Equation for linear (0 to 200 kPa) relationship
WP_kPa=7.407*kOhms/(1-0.018*(T107_C-21))-3.704
'For non-linear (10 to 100 kPa) relationship, use the following equation:
'WP_kPa=kOhms/(0.01306*(1.062*(34.21-T107_C+0.01060*T107_C^2)-kOhms))
CallTable(Hourly) 'Call Data Table and Store Data
NextScan
EndProg
7.3.1.2 Program Example #2 — CR10X with One 107 and One 257
The following example demonstrates the programming used to measure the
resistance (k
Ω) of one 257 sensor with the CR10X datalogger. A 107
temperature probe is measured first for temperature correction of the 257
reading. The linear relationship between sensor resistance and water potential
in the 0 to –200 kPa range is used. For Edlog programming of the non-linear
relationship, see program example #4. Voltage range codes for other Edlog
dataloggers are shown in TABLE 7-2. Sensor wiring for this example is shown
in TABLE 7-6.
TABLE 7-6. Wiring for Programming Example #2
Sensor Wire Function Channel
107 Black Excitation E1
Red Positive Signal SE1 (1H)
Purple Negative Signal AG
Clear Shield G
257 Black Excitation E2
Red Positive Signal SE2 (1L)
White Negative Signal AG
Clear Shield G
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