129 lines
5.4 KiB
Python
129 lines
5.4 KiB
Python
# Temperature measurements with thermistors
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#
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# Copyright (C) 2016-2018 Kevin O'Connor <kevin@koconnor.net>
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#
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# This file may be distributed under the terms of the GNU GPLv3 license.
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import math, logging
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KELVIN_TO_CELCIUS = -273.15
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SAMPLE_TIME = 0.001
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SAMPLE_COUNT = 8
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REPORT_TIME = 0.300
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# Analog voltage to temperature converter for thermistors
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class Thermistor:
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def __init__(self, config, params):
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self.name = config.get_name()
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self.pullup = config.getfloat('pullup_resistor', 4700., above=0.)
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ppins = config.get_printer().lookup_object('pins')
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self.mcu_adc = ppins.setup_pin('adc', config.get('sensor_pin'))
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self.mcu_adc.setup_adc_callback(REPORT_TIME, self.adc_callback)
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self.temperature_callback = None
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self.c1 = self.c2 = self.c3 = 0.
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if 'beta' in params:
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self.calc_coefficients_beta(params, params['beta'])
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else:
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self.calc_coefficients(params)
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def calc_coefficients(self, params):
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# Calculate Steinhart-Hart coefficents from temp measurements.
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# Arrange samples as 3 linear equations and solve for c1, c2, and c3.
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inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS)
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inv_t2 = 1. / (params['t2'] - KELVIN_TO_CELCIUS)
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inv_t3 = 1. / (params['t3'] - KELVIN_TO_CELCIUS)
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ln_r1 = math.log(params['r1'])
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ln_r2 = math.log(params['r2'])
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ln_r3 = math.log(params['r3'])
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ln3_r1, ln3_r2, ln3_r3 = ln_r1**3, ln_r2**3, ln_r3**3
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inv_t12, inv_t13 = inv_t1 - inv_t2, inv_t1 - inv_t3
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ln_r12, ln_r13 = ln_r1 - ln_r2, ln_r1 - ln_r3
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ln3_r12, ln3_r13 = ln3_r1 - ln3_r2, ln3_r1 - ln3_r3
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self.c3 = ((inv_t12 - inv_t13 * ln_r12 / ln_r13)
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/ (ln3_r12 - ln3_r13 * ln_r12 / ln_r13))
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if self.c3 <= 0.:
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beta = ln_r13 / inv_t13
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logging.warn("Using thermistor beta %.3f in heater %s",
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beta, self.name)
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self.calc_coefficients_beta(params, beta)
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return
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self.c2 = (inv_t12 - self.c3 * ln3_r12) / ln_r12
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self.c1 = inv_t1 - self.c2 * ln_r1 - self.c3 * ln3_r1
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def calc_coefficients_beta(self, params, beta):
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# Calculate equivalent Steinhart-Hart coefficents from beta
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inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS)
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ln_r1 = math.log(params['r1'])
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self.c3 = 0.
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self.c2 = 1. / beta
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self.c1 = inv_t1 - self.c2 * ln_r1
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def setup_minmax(self, min_temp, max_temp):
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adc_range = [self.calc_adc(min_temp), self.calc_adc(max_temp)]
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self.mcu_adc.setup_minmax(SAMPLE_TIME, SAMPLE_COUNT,
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minval=min(adc_range), maxval=max(adc_range))
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def setup_callback(self, temperature_callback):
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self.temperature_callback = temperature_callback
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def get_report_time_delta(self):
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return REPORT_TIME
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def adc_callback(self, read_time, read_value):
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# Calculate temperature from adc
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adc = max(.00001, min(.99999, read_value))
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r = self.pullup * adc / (1.0 - adc)
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ln_r = math.log(r)
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inv_t = self.c1 + self.c2 * ln_r + self.c3 * ln_r**3
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temp = 1.0/inv_t + KELVIN_TO_CELCIUS
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self.temperature_callback(read_time + SAMPLE_COUNT * SAMPLE_TIME, temp)
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def calc_adc(self, temp):
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inv_t = 1. / (temp - KELVIN_TO_CELCIUS)
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if self.c3:
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# Solve for ln_r using Cardano's formula
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y = (self.c1 - inv_t) / (2. * self.c3)
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x = math.sqrt((self.c2 / (3. * self.c3))**3 + y**2)
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ln_r = math.pow(x - y, 1./3.) - math.pow(x + y, 1./3.)
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else:
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ln_r = (inv_t - self.c1) / self.c2
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r = math.exp(ln_r)
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return r / (self.pullup + r)
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# Custom defined thermistors from the config file
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class CustomThermistor:
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def __init__(self, config):
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self.name = " ".join(config.get_name().split()[1:])
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t1 = config.getfloat("temperature1", minval=KELVIN_TO_CELCIUS)
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r1 = config.getfloat("resistance1", minval=0.)
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beta = config.getfloat("beta", None, above=0.)
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if beta is not None:
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self.params = {'t1': t1, 'r1': r1, 'beta': beta}
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return
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t2 = config.getfloat("temperature2", minval=KELVIN_TO_CELCIUS)
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r2 = config.getfloat("resistance2", minval=0.)
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t3 = config.getfloat("temperature3", minval=KELVIN_TO_CELCIUS)
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r3 = config.getfloat("resistance3", minval=0.)
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(t1, r1), (t2, r2), (t3, r3) = sorted([(t1, r1), (t2, r2), (t3, r3)])
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self.params = {'t1': t1, 'r1': r1, 't2': t2, 'r2': r2,
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't3': t3, 'r3': r3}
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def create(self, config):
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return Thermistor(config, self.params)
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# Default sensors
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Sensors = {
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"EPCOS 100K B57560G104F": {
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't1': 25., 'r1': 100000., 't2': 150., 'r2': 1641.9,
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't3': 250., 'r3': 226.15 },
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"ATC Semitec 104GT-2": {
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't1': 20., 'r1': 126800., 't2': 150., 'r2': 1360.,
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't3': 300., 'r3': 80.65 },
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"NTC 100K beta 3950": { 't1': 25., 'r1': 100000., 'beta': 3950. },
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}
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def load_config(config):
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# Register default thermistor types
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pheater = config.get_printer().lookup_object("heater")
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for sensor_type, params in Sensors.items():
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func = (lambda config, params=params: Thermistor(config, params))
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pheater.add_sensor(sensor_type, func)
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def load_config_prefix(config):
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thermistor = CustomThermistor(config)
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pheater = config.get_printer().lookup_object("heater")
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pheater.add_sensor(thermistor.name, thermistor.create)
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