Apogee TS-100 Посібник користувача - Сторінка 12

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An excitation voltage of 2.5 V DC is recommended to minimize self-heating and current drain, while still
maintaining adequate measurement sensitivity (mV output from thermistor per C). However, other
excitation voltages can be used. Decreasing the excitation voltage will decrease self-heating and current
drain, but will also decrease thermistor measurement sensitivity. Increasing the excitation voltage will
increase thermistor measurement sensitivity, but will also increase self-heating and current drain.
Conversion of Thermistor Resistance to Temperature:
The thermistor is a resistive element, where resistance changes with temperature. Thermistor resistance
, in ) is measured with a half-bridge measurement, requiring a known excitation voltage input (V
(R
T
and a measurement of output voltage (V
V
 
R
24900
T
V
where 24900 is the resistance of the bridge resistor in . From resistance, temperature (T
calculated with the Steinhart-Hart equation and thermistor specific coefficients:
T
K
A
B
ln(
where A = 1.129241 x 10
If desired, measured temperature in Kelvin can be converted to Celsius (T
T
T
273
.
C
K
PRT:
):
OUT
 
EX
1
OUT
(1)
1
3
R
)
C
(ln(
R
))
(2)
T
T
-3
, B = 2.341077 x 10
.
(3)
15
-4
, and C = 8.775468 x 10
 
, in Kelvin) is
-8
(Steinhart-Hart coefficients).
):
C
12 
)
EX