I'm still convinced it has to use rate of temp rise to do dry coil protection for Kanthal. This will work without knowing the temp accurately but simply knowing it's going up really fast over time and is going up faster and faster over time.
The first derivative, dR/dt, would tell us the rate at which resistance (and thus temp) rises. Second derivative would provide acceleration rate of that rise. I think that's likely enough to make the scheme wattage independent. The inflection point of the second derivative is the "uh oh" she's headed for the moon, spot on any wattage/temp curve.
Here's a photo from an experiment I did a couple years ago. It is the output of a thermocouple on a wet wick/coil. The coil is dry at around five and a half divisions. You can clearly see the inflection point right where the wick gets dry. The wet wick slope (initial rise) is clearly decreasing, while the dry wick slope is clearly increasing. This will happen independent of wattage (within reason -- you can't light it up with a few hundred watts and expect sane results lol). That inflection point of decreasing to sharply increasing slope just past the middle of the screen is it -- dry wick. No need to know the temp to know it's dry.
Also shown is the exponential decay of temp at power off at about eight and a half divisions.
The first derivative, dR/dt, would tell us the rate at which resistance (and thus temp) rises. Second derivative would provide acceleration rate of that rise. I think that's likely enough to make the scheme wattage independent. The inflection point of the second derivative is the "uh oh" she's headed for the moon, spot on any wattage/temp curve.
Here's a photo from an experiment I did a couple years ago. It is the output of a thermocouple on a wet wick/coil. The coil is dry at around five and a half divisions. You can clearly see the inflection point right where the wick gets dry. The wet wick slope (initial rise) is clearly decreasing, while the dry wick slope is clearly increasing. This will happen independent of wattage (within reason -- you can't light it up with a few hundred watts and expect sane results lol). That inflection point of decreasing to sharply increasing slope just past the middle of the screen is it -- dry wick. No need to know the temp to know it's dry.
Also shown is the exponential decay of temp at power off at about eight and a half divisions.
