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heater: Minor cleanup to Steinhart-Hart math 

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-08-18 13:28:04 -04:00
parent 4b5f3bec4b
commit f25cb33367
1 changed files with 12 additions and 11 deletions
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23
klippy/heater.py
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@ -23,30 +23,31 @@ class Thermistor:
ln_r1 = math.log(params['r1'])
ln_r2 = math.log(params['r2'])
ln_r3 = math.log(params['r3'])
ln3_r1, ln3_r2, ln3_r3 = ln_r1**3., ln_r2**3., ln_r3**3.
ln3_r1, ln3_r2, ln3_r3 = ln_r1**3, ln_r2**3, ln_r3**3
inv_t12, inv_t13 = inv_t1-inv_t2, inv_t1 - inv_t3
inv_t12, inv_t13 = inv_t1 - inv_t2, inv_t1 - inv_t3
ln_r12, ln_r13 = ln_r1 - ln_r2, ln_r1 - ln_r3
ln3_r12, ln3_r13 = ln3_r1 - ln3_r2, ln3_r1 - ln3_r3
self.c3 = ((inv_t12 - inv_t13 * ln_r12 / ln_r13)
/ (ln3_r12 - ln3_r13 * ln_r12 / ln_r13))
self.c2 = (inv_t12 - self.c3 * ln3_r12) / ln_r12
self.c1 = inv_t1 - self.c3 * ln3_r1 - self.c2 * ln_r1
self.c1 = inv_t1 - self.c2 * ln_r1 - self.c3 * ln3_r1
def calc_temp(self, adc):
r = self.pullup * adc / (1.0 - adc)
ln_r = math.log(r)
temp_inv = self.c1 + self.c2*ln_r + self.c3*math.pow(ln_r, 3.)
return 1.0/temp_inv + KELVIN_TO_CELCIUS
inv_t = self.c1 + self.c2 * ln_r + self.c3 * ln_r**3
return 1.0/inv_t + KELVIN_TO_CELCIUS
def calc_adc(self, temp):
temp -= KELVIN_TO_CELCIUS
temp_inv = 1./temp
inv_t = 1. / (temp - KELVIN_TO_CELCIUS)
if self.c3:
y = (self.c1 - temp_inv) / (2. * self.c3)
x = math.sqrt(math.pow(self.c2 / (3.*self.c3), 3.) + math.pow(y, 2.))
r = math.exp(math.pow(x-y, 1./3.) - math.pow(x+y, 1./3.))
y = (self.c1 - inv_t) / (2. * self.c3)
x = math.sqrt((self.c2 / (3. * self.c3))**3 + y**2)
ln_r = math.pow(x - y, 1./3.) - math.pow(x + y, 1./3.)
r = math.exp(ln_r)
else:
r = math.exp((temp_inv - self.c1) / self.c2)
ln_r = (inv_t - self.c1) / self.c2
r = math.exp(ln_r)
return r / (self.pullup + r)
# Thermistor calibrated from one temp measurement and its beta