mirror of https://github.com/rusefi/rusefi.git
59 lines
1.4 KiB
C++
59 lines
1.4 KiB
C++
/**
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* @author Matthew Kennedy, (c) 2019
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*/
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#include "pch.h"
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#include "thermistor_func.h"
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#include <math.h>
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SensorResult ThermistorFunc::convert(float ohms) const {
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// This resistance should have already been validated - only
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// thing we can check is that it's non-negative
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if (ohms <= 0) {
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return UnexpectedCode::Low;
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}
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float lnR = logf(ohms);
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float lnR3 = lnR * lnR * lnR;
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float recip = m_a + m_b * lnR + m_c * lnR3;
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float kelvin = 1 / recip;
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float celsius = convertKelvinToCelcius(kelvin);
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// bounds check result - please don't try to run rusEfi when colder than -50C
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// high end limit is required as this could be an oil temp sensor on an
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// air cooled engine
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if (celsius < -50) {
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return UnexpectedCode::Low;
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}
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if (celsius > 250) {
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return UnexpectedCode::High;
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}
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return celsius;
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}
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void ThermistorFunc::configure(thermistor_conf_s &cfg) {
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// https://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation
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float l1 = logf(cfg.resistance_1);
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float l2 = logf(cfg.resistance_2);
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float l3 = logf(cfg.resistance_3);
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float y1 = 1 / convertCelsiusToKelvin(cfg.tempC_1);
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float y2 = 1 / convertCelsiusToKelvin(cfg.tempC_2);
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float y3 = 1 / convertCelsiusToKelvin(cfg.tempC_3);
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float u2 = (y2 - y1) / (l2 - l1);
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float u3 = (y3 - y1) / (l3 - l1);
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m_c = ((u3 - u2) / (l3 - l2)) / (l1 + l2 + l3);
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m_b = u2 - m_c * (l1 * l1 + l1 * l2 + l2 * l2);
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m_a = y1 - (m_b + l1 * l1 * m_c) * l1;
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}
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