Cypress CY8CKIT-025, Руководство пользователя

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CY8CKIT-025 PSoC® Precision Analog Temperature Sensor Expansion Board Kit Guide, Doc. # 001-65791 Rev. *J 24
4. Hardware
4.1 System Block Diagram and Theory of System Operation
The schematic of the CY8CKIT-025 PSoC Precision Analog Temperature Sensor EBK is shown in
the
Appendix on page 83 . The circuits associated with each temperature sensor are boxed
individually. This section gives a description of each circuit and the temperature equations involved
in each method.
4.2 Thermocouple
Cypress application note AN75511 - PSoC 3/PSoC 5LP Temperature Measurement with a
Thermocouple explains the theory behind the thermocouple terminology; see the application note to
understand thermocouple temperature measurement. This section assumes that you have prior
knowledge of thermocouple terminology.
A thermocouple gives an output voltage that is directly related to the temperature difference between
two metallic junctions. The output voltage is not linearly related to temperature. The output voltage
versus temperature curve can be considered piece-wise linear with different slopes in different
temperature ranges. The relation between hot junction voltage and cold junction voltage is given by
the following equation.
Equation 1
where the value of
K
depends on the temperature range.
V1
is the voltage across the hot junction
and
V2
is the cold junction compensation (CJC) voltage (see AN75511 for details on cold junction
compensation).
T
is the hot junction temperature.
Figure 4-1 shows the circuit used for thermocouple temperature measurement. A three-channel
ADC is used.
■
Channel 0 is used for thermocouple voltage measurement
■
Channel 1 is used for cold junction compensation
■
Channel 2 is used for offset cancellation
V2 KT V1
 