Well, in a sense, nobody but the engineers at the company really know how they work. The algorithms are proprietary. For instance, if you knew the physical parameters of your system... conductivities, spec. heat etc, and you knew what the pid was actually doing, you could set the pid parameters to have it work optimally. Instead, you use 'informed' trial and error or 'AUTOTUNE.' Believe me, I spent many hours in grad school trying to extract info from Watlow about their pids.
So what is it about these stills that we are trying to keep constant, and why? Those who run electric stills have another precise way to regulate performance, but manipulation of this variable seldom gets mention.
'Bubble cap plates are better for batch distillation than perforated plates' - Benjamin Franklin
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