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# Temperature measurements with thermistors
#
# Copyright (C) 2016-2018 Kevin O'Connor <kevin@koconnor.net>
#
# This file may be distributed under the terms of the GNU GPLv3 license.
import math, logging
KELVIN_TO_CELCIUS = -273.15
SAMPLE_TIME = 0.001
SAMPLE_COUNT = 8
REPORT_TIME = 0.300
# Analog voltage to temperature converter for thermistors
class Thermistor:
def __init__(self, config, params):
self.name = config.get_name()
self.pullup = config.getfloat('pullup_resistor', 4700., above=0.)
ppins = config.get_printer().lookup_object('pins')
self.mcu_adc = ppins.setup_pin('adc', config.get('sensor_pin'))
self.mcu_adc.setup_adc_callback(REPORT_TIME, self.adc_callback)
self.temperature_callback = None
self.c1 = self.c2 = self.c3 = 0.
if 'beta' in params:
self.calc_coefficients_beta(params, params['beta'])
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)
inv_t2 = 1. / (params['t2'] - KELVIN_TO_CELCIUS)
inv_t3 = 1. / (params['t3'] - KELVIN_TO_CELCIUS)
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
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))
if self.c3 <= 0.:
beta = ln_r13 / inv_t13
logging.warn("Using thermistor beta %.3f in heater %s",
beta, self.name)
self.calc_coefficients_beta(params, beta)
return
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, beta):
# 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. / beta
self.c1 = inv_t1 - self.c2 * ln_r1
def setup_minmax(self, min_temp, max_temp):
adc_range = [self.calc_adc(min_temp), self.calc_adc(max_temp)]
self.mcu_adc.setup_minmax(SAMPLE_TIME, SAMPLE_COUNT,
minval=min(adc_range), maxval=max(adc_range))
def setup_callback(self, temperature_callback):
self.temperature_callback = temperature_callback
def get_report_time_delta(self):
return REPORT_TIME
def adc_callback(self, read_time, read_value):
# Calculate temperature from adc
adc = max(.00001, min(.99999, read_value))
r = self.pullup * adc / (1.0 - adc)
ln_r = math.log(r)
inv_t = self.c1 + self.c2 * ln_r + self.c3 * ln_r**3
temp = 1.0/inv_t + KELVIN_TO_CELCIUS
self.temperature_callback(read_time + SAMPLE_COUNT * SAMPLE_TIME, temp)
def calc_adc(self, temp):
inv_t = 1. / (temp - KELVIN_TO_CELCIUS)
if self.c3:
# Solve for ln_r using Cardano's formula
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.)
else:
ln_r = (inv_t - self.c1) / self.c2
r = math.exp(ln_r)
return r / (self.pullup + r)
# Custom defined thermistors from the config file
class CustomThermistor:
def __init__(self, config):
self.name = " ".join(config.get_name().split()[1:])
t1 = config.getfloat("temperature1", minval=KELVIN_TO_CELCIUS)
r1 = config.getfloat("resistance1", minval=0.)
beta = config.getfloat("beta", None, above=0.)
if beta is not None:
self.params = {'t1': t1, 'r1': r1, 'beta': beta}
return
t2 = config.getfloat("temperature2", minval=KELVIN_TO_CELCIUS)
r2 = config.getfloat("resistance2", minval=0.)
t3 = config.getfloat("temperature3", minval=KELVIN_TO_CELCIUS)
r3 = config.getfloat("resistance3", minval=0.)
(t1, r1), (t2, r2), (t3, r3) = sorted([(t1, r1), (t2, r2), (t3, r3)])
self.params = {'t1': t1, 'r1': r1, 't2': t2, 'r2': r2,
't3': t3, 'r3': r3}
def create(self, config):
return Thermistor(config, self.params)
# Default sensors
Sensors = {
"EPCOS 100K B57560G104F": {
't1': 25., 'r1': 100000., 't2': 150., 'r2': 1641.9,
't3': 250., 'r3': 226.15 },
"ATC Semitec 104GT-2": {
't1': 20., 'r1': 126800., 't2': 150., 'r2': 1360.,
't3': 300., 'r3': 80.65 },
"NTC 100K beta 3950": { 't1': 25., 'r1': 100000., 'beta': 3950. },
"Honeywell 100K 135-104LAG-J01": { 't1': 25., 'r1': 100000., 'beta': 3974. },
"NTC 100K MGB18-104F39050L32": { 't1': 25., 'r1': 100000., 'beta': 4100. },
}
def load_config(config):
# Register default thermistor types
pheater = config.get_printer().lookup_object("heater")
for sensor_type, params in Sensors.items():
func = (lambda config, params=params: Thermistor(config, params))
pheater.add_sensor(sensor_type, func)
def load_config_prefix(config):
thermistor = CustomThermistor(config)
pheater = config.get_printer().lookup_object("heater")
pheater.add_sensor(thermistor.name, thermistor.create)
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