• Chris Lesiak's avatar
    hwmon: (ntc_thermistor) Improve precision of resistance calculation · f6725ae2
    Chris Lesiak authored
    The function get_ohm_of_thermistor has both the measured voltage and the
    pullup voltage available in microvolts.  But it was promptly converting
    both to millivolts before using them to calculate the thermistor
    resistance.  That conversion unnecessarily hurt the precision of the
    calculation.
    
    For example, take the ncpXXwb473 connected to 5000 mV and pulled down
    through a 47000 ohm resistor.  At 25 C, the resistance of the thermistor
    is 47000 ohms.  The measured voltage will be 2500 mV.  If we measure
    instead 2501 mV, then the calculated resistance will be 46962 ohms --
    a difference of 38 ohms.  So the precision of the resistance estimate
    could be increased by 38X by doing the calculations in microvolts.
    Signed-off-by: default avatarChris Lesiak <chris.lesiak@licor.com>
    Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
    f6725ae2
ntc_thermistor.c 18.4 KB