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jmoore52 / SkywalkerRoaster

Artisian control of Skywalker Electric Coffee Roaster via Arduino.
GNU General Public License v3.0
56 stars 7 forks source link

temperature logic #10

Open panigrah opened 7 months ago

panigrah commented 7 months ago

Hey is the logic to calculate temperature likely because its a raw thermistor resistance reading? Steinhart-Hart Equation

renatoa commented 5 months ago

Probably yes, but you know the voltage and resistances involved?

Also, please be aware that the thermistor is used in two modes, by changing polarization and taking two measurements for each sample. The two measurements are sent as two data values in the temperature packet of the protocol. The reason of this operation mode is unknown, what follows is just my guess. An educated guess... industry automation engineer. It is supposed that many parts and code in this machine were taken from other project, possible an espresso water boiler, where temperature processing was been optimized for up to 130C degrees. Because in a roaster there are temperatures much higher than in boiler water, they changed the NTC to a model with extended range, up to 270C probably, where the overheating logic kicks and shutdown machine. Also, because of the higher non-linearity of this NTC, they divided the whole range in two subranges, for each of them polarizing the NTC optimized for greatest linearity in the subrange. Thus, the equation above must be applied for each range separately, using its own data from the packet.

billsey commented 3 months ago

I believe the latest info here (https://homeroasters.org/forum/viewthread.php?thread_id=6979&rowstart=350#post_78985) is correct.

renatoa commented 3 months ago

Two posts below I added more on same subject.