mhu/reflow-oven-control-sw
2
0
Fork 0
Code Issues 4 Pull Requests Releases 4 Wiki Activity

Issue #26: Add reverse lookup function to temp converter that converts a temperature to a PT1000 resistance value

Browse Source
This commit is contained in:
Mario Hüttel 2021-02-02 19:32:12 +01:00
parent 0b01be9840
commit 64bb06882f
2 changed files with 56 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
stm-firmware/include/reflow-controller/temp-converter.h
View File

@ -29,4 +29,13 @@
*/
int temp_converter_convert_resistance_to_temp(float resistance, float *temp_out);
/**
* @brief Convert temperature to PT1000 resistance
* @param temp Temperature in degrees celsius
* @param[out] resistance_out Resistance value
* @return 0 if ok, -1 if tmeperature is below the lookup table, 1 if value is above the lookup table, -1000 in case of a pointer error,
* -100 if an internal error occured. This should never happen, if the lookup table is correct
*/
int temp_convertet_convert_temp_to_resistance(float temp, float *resistance_out);
#endif /* __TEMP_CONVERTER_H__ */

47
stm-firmware/temp-converter.c
View File

@ -21,6 +21,7 @@
#include <reflow-controller/temp-converter.h>
#include <reflow-controller/temp-converter-data.h>
#include <helper-macros/helper-macros.h>
#include <stdbool.h>
static const float temp_lookup[(TEMP_CONVERSION_MAX_RES-TEMP_CONVERSION_MIN_RES) / TEMP_CONVERSION_RES_STEP+1] = {TEMP_CONVERSION_ARRAY_DATA};
@ -73,3 +74,49 @@ int temp_converter_convert_resistance_to_temp(float resistance, float *temp_out)
return_ret_val:
return ret_val;
}
int temp_convertet_convert_temp_to_resistance(float temp, float *resistance_out)
{
int retcode = 0;
unsigned int i;
float lower_temp;
float upper_temp;
float lower_resistance;
float upper_resistance;
float temp_ratio;
bool found = false;
if (!resistance_out)
return -1000;
if (temp < temp_lookup[0]) {
/* Requested temperature is smaller than minimum value in lookup table */
*resistance_out = temp_lookup[0];
retcode = -1;
goto exit;
} else if (temp > temp_lookup[COUNT_OF(temp_lookup) - 1]) {
/* Requested temperature is higher than maximum value in lookup table */
*resistance_out = temp_lookup[COUNT_OF(temp_lookup) -1];
retcode = 1;
goto exit;
}
for (i = 0U; i < (COUNT_OF(temp_lookup) - 1); i++) {
if (temp >= temp_lookup[i] && temp <= temp_lookup[i+1]) {
upper_temp = temp_lookup[i+1];
lower_temp = temp_lookup[i];
lower_resistance = TEMP_CONVERSION_MIN_RES + TEMP_CONVERSION_RES_STEP * (i);
upper_resistance = lower_resistance + TEMP_CONVERSION_RES_STEP;
found = true;
}
}
if (!found)
return -100;
temp_ratio = (temp - lower_temp) / (upper_temp - lower_temp);
*resistance_out = lower_resistance + (upper_resistance - lower_resistance) * temp_ratio;
exit:
return retcode;
}