Campbell Scientific 109SS Temperature Probe - Manual (Page 24)

Appendix B. Example Programs
'*AG = Analog Ground (represented by ground symbol on CR1000 wiring panel
'Declare the variables for the temperature measurement
Public T109_C
'Define a data table for 60 minute averages
DataTable (Table1,True,-1)
DataInterval (0,10,Min,10)
Average (1,T109_C,FP2,False)
EndTable
'Main Program
BeginProg
Scan (1,Sec,1,0)
'Measure the temperature
Therm109 (T109_C,1,1,1,0,_60Hz,1.0,0)
'Call Data Table
CallTable (Table1)
NextScan
EndProg
B.1.3 Example 3 — Sample Program using the BrHalf()
instruction rather than Therm109()
‘Program measures a single 109 Thermistor probe once a second and
‘stores the average temperature every 60 minutes.
'Wiring Diagram
'==============
'109SS Probe
'
' Wire
' Color Function CR1000
' ----- -------- ------
' Black Voltage-excitation input VX1 or EX1
' Red Analog-voltage output SE1
' Purple Bridge-resistor ground AG*
' Clear Shield G*
'*AG = Analog Ground (represented by ground symbol on CR1000 wiring panel
'Declare the variables for the temperature measurement
Public T109_C
'Declare variables for the raw measurement, thermistor resistance,
‘and ln(resistance):
Dim V_Vx, Rtherm, lnRt
'Define a data table for 60 minute averages
DataTable (Table1,True,-1)
DataInterval (0,10,Min,10)
Average (1,T109_C,IEEE4,False)
EndTable
BeginProg
Scan (1,sec,5,0)
'Measure the 109SS probe. The result is V/Vx.
BrHalf (V_Vx,1,mV5000,3,Vx1,1,5000,True,0,_60Hz,1.0,0)
'Calculate reistance:
RTherm=24900 * (1 / V_Vx-1)
'Calculate the natural log of the resistance
lnRt= Log (Rtherm)
'Apply the Steinhart-Hart equation and convert to degrees C in one step:
Air_Temp=1 / (1.129241e-3 + 2.341077e-4 * lnRt + 8.775468e-8 * (lnRt ^ 3)) - 273.15
B-2