[time-nuts] uC ADC resolution (was: Poor man's oven)
hmurray at megapathdsl.net
Sat Jun 10 21:11:43 EDT 2017
albertson.chris at gmail.com said:
> I say "effective" because we can dither the low order bits to gain maybe 6
> effective bits form 4 real bits (we can filter the switching noise from a
> low frequency dither)
It's hard to filter low frequencies and the more bits you gain by dithering
the lower the filter you need and the closer in the spurs move.
> Lets say my goal is regulation within 0.1C. After filtering I have 10
> "good" bits in my ADC. That is 1024 counts. My set point is S.
> I scale the ADC so that 0 == (S - 0.5) and 1023 == (S + 0.5) This means
> that each ADC count is 0.001 degree C and within the 0.1C range there are
> 100 ADC counts.
That's not enough to describe the system so you can decide if it will meet
your 0.1C goal.
You also need to know the sampling rate, the delay time from heater to
temperature sensor, the PID parameters, and maybe the rate of change of the
environmental temperature and the delay from the environment to your system.
("delay" should probably be transfer function or impulse response but a
simple exponential is probably good enough.)
These are my opinions. I hate spam.
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