diff options
Diffstat (limited to 'klippy/heater.py')
| -rw-r--r-- | klippy/heater.py | 28 |
1 files changed, 15 insertions, 13 deletions
diff --git a/klippy/heater.py b/klippy/heater.py index eb086c25..f8031538 100644 --- a/klippy/heater.py +++ b/klippy/heater.py @@ -12,10 +12,16 @@ import math, logging, threading KELVIN_TO_CELCIUS = -273.15 -# Thermistor calibrated with three temp measurements +# Analog voltage to temperature converter for thermistors class Thermistor: def __init__(self, config, params): self.pullup = config.getfloat('pullup_resistor', 4700., above=0.) + self.c1 = self.c2 = self.c3 = 0. + if 'beta' in params: + self.calc_coefficients_beta(params) + else: + self.calc_coefficients(params) + def calc_coefficients(self, params): # Calculate Steinhart-Hart coefficents from temp measurements. # Arrange samples as 3 linear equations and solve for c1, c2, and c3. inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS) @@ -34,6 +40,13 @@ class Thermistor: / (ln3_r12 - ln3_r13 * ln_r12 / ln_r13)) self.c2 = (inv_t12 - self.c3 * ln3_r12) / ln_r12 self.c1 = inv_t1 - self.c2 * ln_r1 - self.c3 * ln3_r1 + def calc_coefficients_beta(self, params): + # Calculate equivalent Steinhart-Hart coefficents from beta + inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS) + ln_r1 = math.log(params['r1']) + self.c3 = 0. + self.c2 = 1. / params['beta'] + self.c1 = inv_t1 - self.c2 * ln_r1 def calc_temp(self, adc): adc = max(.00001, min(.99999, adc)) r = self.pullup * adc / (1.0 - adc) @@ -52,17 +65,6 @@ class Thermistor: r = math.exp(ln_r) return r / (self.pullup + r) -# Thermistor calibrated from one temp measurement and its beta -class ThermistorBeta(Thermistor): - def __init__(self, config, params): - self.pullup = config.getfloat('pullup_resistor', 4700., above=0.) - # Calculate Steinhart-Hart coefficents from beta - inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS) - ln_r1 = math.log(params['r1']) - self.c3 = 0. - self.c2 = 1. / params['beta'] - self.c1 = inv_t1 - self.c2 * ln_r1 - # Linear style conversion chips calibrated with two temp measurements class Linear: def __init__(self, config, params): @@ -84,7 +86,7 @@ Sensors = { 'class': Thermistor, 't1': 20., 'r1': 126800., 't2': 150., 'r2': 1360., 't3': 300., 'r3': 80.65 }, "NTC 100K beta 3950": { - 'class': ThermistorBeta, 't1': 25., 'r1': 100000., 'beta': 3950. }, + 'class': Thermistor, 't1': 25., 'r1': 100000., 'beta': 3950. }, "AD595": { 'class': Linear, 't1': 25., 'v1': .25, 't2': 300., 'v2': 3.022 }, } |