Campbell Scientific 109 109-L Temperature Probe - Page 18

Electrically Noisy Environments

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Model 109 Temperature Probe TABLE 8-2. 109-Temperature Calculation CRBasic Dataloggers1 Therm109() instruction measures the ratio Vs/Vx, calculates the thermistor resistance Rs, and converts Rs to temperature using the Steinhart-Hart equation2: T = 1 / (A + (B • ln(Rs))) + (C • ((ln(Rs))) ^ 3) - 273.15 where: T = temperature in degrees Celsius A = 1.129241E-3 B = 2.341077E-4 C = 8.775468E-8 Edlog Dataloggers3 AC Half Bridge (P5) instruction measures the ratio Vs/Vx. Mathematical instructions calculate and pre-scale ln(Rs) by 1E-3. This creates adequate resolution for Polynomial (P55) instruction to apply the Steinhart-Hart equation with a fifth-order polynomial. The inverse of the result, Tk, is found with the Z=1/X (P42) instruction: 1/Tk = C0 + C1•X + C2•X^2 + C3•X^3 + C4•X^4 + C5•X^5 where: Tk = temperature in Kelvin X = 0.001 • ln(Rs) C0 = A = 0.001129 C1 = B • 1E3 = 0.234108 C2 = 0 C3 = C • 1E9 = 87.7547 C4 = 0 C5 = 0 See Appendix C, Thermistor Resistance Table. 1CRBasic dataloggers are CR800, CR1000, CR3000, and CR5000. 2Coefficients provided by the thermistor manufacturer. 3Edlog dataloggers are CR10(X), CR510, CR500, CR23X, 21X, and CR7. 8.3 Electrically Noisy Environments EMF noise emanating from the ac mains power grid can be a significant source of measurement error. 60 Hz noise is common in the United States. 50 Hz noise is common in Europe and other regions. Depending on the datalogger model, this noise can usually be filtered out. The following code examples filter 60 Hz noise. The key parameters are in bold type. CRBasic Therm109(T109_C,1,1,1,20000,_60Hz,1.0,0.0) NOTE Filtering parameter options are not available for CR200(X) series dataloggers. 12

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Model 109 Temperature Probe
TABLE 8-2.
109-Temperature Calculation
CRBasic Dataloggers
1
Therm109()
instruction measures the ratio Vs/Vx, calculates the thermistor resistance
Rs, and converts Rs to temperature using the Steinhart-Hart equation
2
:
T = 1 / (A + (B • ln(Rs))) + (C • ((ln(Rs))) ^ 3)
– 273.15
where:
T = temperature in degrees Celsius
A = 1.129241E–3
B = 2.341077E–4
C = 8.775468E–8
Edlog Dataloggers
3
AC Half Bridge (P5)
instruction measures the ratio Vs/Vx.
Mathematical instructions
calculate and pre-scale ln(Rs) by 1E–3.
This creates adequate resolution for
Polynomial (P55)
instruction to apply the Steinhart-Hart equation with a fifth-order
polynomial.
The inverse of the result, Tk, is found with the
Z=1/X (P42)
instruction:
1/Tk = C0 + C1•X + C2•X^2 + C3•X^3 + C4•X^4 + C5•X^5
where:
Tk = temperature in Kelvin
X = 0
.001 • ln(Rs)
C0 = A = 0.001129
C1 = B •
1E3 = 0.234108
C2 = 0
C3 = C •
1E9 = 87.7547
C4 = 0
C5 = 0
See Appendix C,
Thermistor Resistance Table
.
1
CRBasic dataloggers are CR800, CR1000, CR3000, and CR5000.
2
Coefficients provided by the thermistor manufacturer.
3
Edlog dataloggers are CR10(X), CR510, CR500, CR23X, 21X, and CR7.
8.3
Electrically Noisy Environments
EMF noise emanating from the ac mains power grid can be a significant source
of measurement error.
60 Hz noise is common in the United States.
50 Hz
noise is common in Europe and other regions.
Depending on the datalogger
model, this noise can usually be filtered out.
The following code examples filter 60 Hz noise.
The key parameters are in
bold type.
CRBasic
Therm109
(
T109_C
,1,1,1,20000,
_60Hz
,1.0,0.0)
Filtering parameter options are not available for CR200(X) series
dataloggers.
NOTE
12