CY8CKIT-025 PSoC® Precision Analog Temperature Sensor Expansion Board Kit Guide, Doc. # 001-65791 Rev. *J
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Hardware
Figure 4-3. RTD Circuit Diagram
One of the PSoC 3 or PSoC 5LP IDACs is used to force a current through the RTD, and the delta
sigma ADC is used to measure the voltage across the RTD. The RTD resistance (V/I) is calculated
and hence the temperature is obtained. Precise 100-
(0.1%) reference resistance is used to
accurately measure the current forced using IDAC, thereby eliminating any gain error and drift
associated with the ADC and IDAC. First the IDAC current is passed through the reference resistor
(Rref) and the voltage across the reference resistor (Vref) is measured using ADC. The same current
is then passed through the RTD and the voltage across RTD (Vrtd) is also measured using ADC.
The RTD resistance is calculated using the equation:
Equation 6
PSoC Creator provides an RTD component that helps to convert resistance to temperature.
IDAC
ADC
R
RTD
100 ohm
0.1%
20 ohm
20 ohm
0
1
2
)
(Vref/Rref
Vrtd
R
RTD
