Atmel Xplained Evaluation Board ATXMEGAA3BU-XPLD ATXMEGAA3BU-XPLD データシート
製品コード
ATXMEGAA3BU-XPLD
4
AVR1934
8413A-AVR-09/11
2.3 NTC temperature sensor
An NTC (Negative Temperature Coefficient) resistor is available for measurement of
the ambient temperature. The NTC resistor is connected in series with another
resistor, creating a voltage across the NTC resistor which varies with the ambient
temperature. This voltage can in turn be measured using the Atmel AVR XMEGA
ADC. The relationship between the ADC sample values and the actual ambient
temperature is a complex equation shown in the plot in Figure 2-1:
the ambient temperature. The NTC resistor is connected in series with another
resistor, creating a voltage across the NTC resistor which varies with the ambient
temperature. This voltage can in turn be measured using the Atmel AVR XMEGA
ADC. The relationship between the ADC sample values and the actual ambient
temperature is a complex equation shown in the plot in Figure 2-1:
Figure 2-1.
Comparison of real data with linearized approximation
To calculate the actual temperature efficiently using the XMEGA device, linearization
of the relationship between ADC samples and temperature is chosen, using the
following equations:
of the relationship between ADC samples and temperature is chosen, using the
following equations:
T[°C]
= -0.07776 * ADCsample + 65.513 [0 < ADCsample < 420]
T[°C]
= -0.04748 * ADCsample + 53.25728 [420 ≤ ADCsample < 697]
T[°C]
= -0.0295 * ADCsample + 40.50229 [697 ≤ ADCsample ≤ 2047],
where
ADCsample
is the value obtained from the ADC. The accuracy of the resulting
temperature is only as accurate as the regression method used. As the equation