Apogee TS-100 Посібник користувача - Сторінка 13

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Measurement of PRT resistance is very similar to measurement of thermistor resistance, where a half-
bridge measurement is used. An excitation voltage is input across the bridge resistor and an output
voltage is measured across the PRT.
An excitation voltage of 2.1 V DC is recommended to minimize current drain, while still maintaining an
adequate voltage signal. However, other excitation voltages can be used. Decreasing the excitation
voltage will decrease current drain, but will also decrease output voltage. Increasing the excitation
voltage will increase output voltage, but will also increase current drain.
Conversion of PRT Resistance to Temperature:
The PRT is a resistive element, where resistance changes with temperature. PRT resistance (R
measured with a half-bridge measurement, requiring a known excitation voltage input (V
measurement of output voltage (V
1000
V
R
PRT
V
V
EX
where 10000 is the resistance of the bridge resistor in . From resistance, temperature (T
calculated with a second order polynomial and PRT-specific coefficients:
2
T
C
2
R
C
PRT
where C2, C1, and C0 are coefficients determined from factory calibration and provided on a calibration
sheet included with the PRT.
):
OUT
OUT
(1)
OUT
(2)
C
1
R
C
0
PRT
 
13 
, in ) is
PRT
) and a
EX
, in Celsius) is
C