arofarn/Adafruit_MicroPython_MAX31685
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Add resistance property.

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This commit is contained in:
Tony DiCola 2017-12-15 15:15:23 -08:00
parent 2151dda2f9
commit d6213b35b4
1 changed files with 14 additions and 8 deletions
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22
adafruit_max31865.py
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@ -194,19 +194,25 @@ class MAX31865:
rtd >>= 1 rtd >>= 1
return rtd return rtd
@property
def resistance(self):
"""Read the resistance of the RTD and return its value in Ohms."""
resistance = self.read_rtd()
resistance /= 32768
resistance *= self.ref_resistor
return resistance
@property @property
def temperature(self): def temperature(self):
"""Read the temperature of the sensor and return its value in degrees """Read the temperature of the sensor and return its value in degrees
Celsius. Celsius.
""" """
raw_reading = self.read_rtd()
raw_reading /= 32768
raw_reading *= self.ref_resistor
# This math originates from: # This math originates from:
# http://www.analog.com/media/en/technical-documentation/application-notes/AN709_0.pdf # http://www.analog.com/media/en/technical-documentation/application-notes/AN709_0.pdf
# To match the naming from the app note we tell lint to ignore the Z1-4 naming. # To match the naming from the app note we tell lint to ignore the Z1-4
# naming.
# pylint: disable=invalid-name # pylint: disable=invalid-name
raw_reading = self.resistance
Z1 = -_RTD_A Z1 = -_RTD_A
Z2 = _RTD_A * _RTD_A - (4 * _RTD_B) Z2 = _RTD_A * _RTD_A - (4 * _RTD_B)
Z3 = (4 * _RTD_B) / self.rtd_nominal Z3 = (4 * _RTD_B) / self.rtd_nominal
@ -220,10 +226,10 @@ class MAX31865:
temp += 2.2228 * rpoly temp += 2.2228 * rpoly
rpoly *= raw_reading # square rpoly *= raw_reading # square
temp += 2.5859e-3 * rpoly temp += 2.5859e-3 * rpoly
rpoly *= raw_reading # ^3 rpoly *= raw_reading # ^3
temp -= 4.8260e-6 * rpoly temp -= 4.8260e-6 * rpoly
rpoly *= raw_reading # ^4 rpoly *= raw_reading # ^4
temp -= 2.8183e-8 * rpoly temp -= 2.8183e-8 * rpoly
rpoly *= raw_reading # ^5 rpoly *= raw_reading # ^5
temp += 1.5243e-10 * rpoly temp += 1.5243e-10 * rpoly
return temp return temp