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| author | Kevin O'Connor <kevin@koconnor.net> | 2018-04-09 12:35:18 -0400 |
|---|---|---|
| committer | Kevin O'Connor <kevin@koconnor.net> | 2018-04-09 12:35:18 -0400 |
| commit | 75b89f5261f01eac6372d2adcedb878ce9f562f6 (patch) | |
| tree | 5672d0952c6b06d7c44e5dc002bc9ca2f77c1d6b /klippy | |
| parent | 8c8261ba8009b5c16815cb5166d50f7269d786cc (diff) | |
| download | kutter-75b89f5261f01eac6372d2adcedb878ce9f562f6.tar.gz kutter-75b89f5261f01eac6372d2adcedb878ce9f562f6.tar.xz kutter-75b89f5261f01eac6372d2adcedb878ce9f562f6.zip | |
thermistor: Fallback to using beta if Steinhart-Hart c3 is negative
If the c3 coefficient is negative it can cause the adc calculations to
fail. The c3 shouldn't be negative in practice, so fallback to a
simple beta calculation in that case.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Diffstat (limited to 'klippy')
| -rw-r--r-- | klippy/extras/thermistor.py | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/klippy/extras/thermistor.py b/klippy/extras/thermistor.py index cc2d64fd..a7e6c5d7 100644 --- a/klippy/extras/thermistor.py +++ b/klippy/extras/thermistor.py @@ -3,7 +3,7 @@ # 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 +import math, logging KELVIN_TO_CELCIUS = -273.15 SAMPLE_TIME = 0.001 @@ -13,6 +13,7 @@ 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')) @@ -20,7 +21,7 @@ class Thermistor: self.temperature_callback = None self.c1 = self.c2 = self.c3 = 0. if 'beta' in params: - self.calc_coefficients_beta(params) + self.calc_coefficients_beta(params, params['beta']) else: self.calc_coefficients(params) def calc_coefficients(self, params): @@ -40,14 +41,20 @@ class Thermistor: 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): + 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. / params['beta'] + 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)] |