//
// This is a thermistor temperature estimator component for LinuxCNC.
// Copyright 2015-2016 Sebastian Kuzminsky <seb@highlab.com>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//
component thermistor "compute temperature indicated by a thermistor";
license "GPL";
option userspace yes;
option userinit;
option extra_link_args "-lm";
description """This component computes the temperature indicated by a
thermistor in a voltage-divider ladder. It uses the Beta-parameter
variant of the Steinhart-Hart equation, described here:
http://en.wikipedia.org/wiki/Thermistor""";
include <unistd.h>;
include <rtapi_math.h>;
pin in float t0_c """Reference temperature of the thermistor, in degrees
Celsius (typically 25 C). This must be set before the component can
compute the thermistor temperature. The reference temperature information
is supplied by the thermistor manufacturer.""";
pin in float r0 """Resistance of the thermistor at the reference
temperature. This must be set before the component can compute the
thermistor temperature. The reference resistance information is supplied
by the thermistor manufacturer.""";
pin in float beta """Beta parameter of the thermistor (sometimes
just called B). This must be set before the component can compute the
thermistor temperature. The Beta parameter is supplied by the thermistor
manufacturer.""";
pin in float r_other """Resistance of the other resistor in the
voltage-divider ladder. This must be set before the component can
compute the thermistor temperature.""";
pin in float v_total "Supply voltage of the voltage-divider ladder.";
pin in float v_thermistor "Voltage drop across the termistor.";
pin out float temperature_c "Temperature sensed by the thermistor, in degrees Celsius.";
pin out float temperature_k "Temperature sensed by the thermistor, in Kelvins.";
pin out float temperature_f "Temperature sensed by the thermistor, in degrees Fahrenheit.";
pin out float resistance "Computed resistance of the thermistor.";
;;
#include <signal.h>
int should_exit = 0;
void sigterm_handler(int signo) {
should_exit = 1;
}
static void userinit(int argc, char **argv) {
signal(SIGTERM, sigterm_handler);
}
void user_mainloop(void) {
while (!should_exit) {
FOR_ALL_INSTS() {
hal_float_t t0_k = t0_c + 273.15;
hal_float_t r_inf;
hal_float_t current;
if (t0_k <= 0.0) {
goto problem;
}
if (r_other <= 0.0) {
goto problem;
}
r_inf = r0 * exp(-beta/t0_k);
if (r_inf <= 0.0) {
goto problem;
}
current = (v_total - v_thermistor) / r_other;
if (current <= 0.0) {
goto problem;
}
resistance = v_thermistor / current;
if (isnan(resistance) || isinf(resistance) || (resistance <= 0.0)) {
goto problem;
}
temperature_k = beta / log(resistance/r_inf);
if (isnan(temperature_k) || isinf(temperature_k) || (temperature_k < 0.0)) {
goto problem;
}
// no problems found
goto ok;
problem:
// override problematic output pins with bogus but not invalid values
resistance = 0;
temperature_k = 9999;
ok:
temperature_c = temperature_k - 273.15;
temperature_f = (temperature_c * 9.0 / 5.0) + 32.0;
}
usleep(100 * 1000);
}
}