Model 109SS Temperature Probe
5.1.1.3 Sample Program for CR5000
'CR5000
'This example program measures a single 109 Thermistor probe
'once a second and stores the average temperature every 10 minutes.
'Declare the variable for the temperature.
Public Air_Temp
'Declare variables for the raw measurement, thermistor resistance, and ln(resistance):
Dim V_Vx, Rtherm, lnRt
'Define a data table for 10 minute averages:
DataTable (AvgTemp,1,1000)
DataInterval
(0,10,min,10)
Average
(1,Air_Temp,IEEE4,0)
EndTable
BeginProg
Scan (1 ,sec,5,0)
'Measure the 109 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 and 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
'Call the data table:
CallTable
AvgTemp
NextScan
EndProg
5.2 Edlog
In Edlog, Instruction 5 is typically used to measure the 109SS resistance.
Instruction 55 is used to apply the Steinhart and Hart equation. Instruction 55
does not allow entering the coefficients with scientific notation. In order to use
this instruction with as much resolution as possible, the ln resistance term is
pre scaled by 10
-3
. This allows the first order coefficient (B) to be multiplied
by 10
3
, and the 3
rd
order coefficient (C) to be multiplied by 10
9
(see Section
5.2.1).
5.2.1 Example Edlog Program
TABLE 5-2. Wiring for Example Program
Color Description
CR10X
Black Excitation
E1
Red Signal
SE1
Purple
Signal Ground
AG
Clear Shield
G
7
