On Sun, Oct 20, 2024 at 12:32 AM Steve Litt <slitt@???> wrote:
>
> o1bigtenor via Dng said on Sat, 19 Oct 2024 11:57:05 -0500
>
>
> >The process I am working toward controlling will have a water bath for
> >process control temperature. I must have the air over the process 1 C
> >warmer than the process. Vat T must be provably uniform (constant slow
> >speed stirring).
>
> How are you going to prove it? How many temperature sensors will be in
> the vat to prove uniformity?

Typically (other people's versions) there is a 6 wire PTD (I think
that is the acronym)
- - - temperature sensor that is placed into the stirred stream. The
stirring mechanism
is considered adequate to keep the T uniform.
>
>
> > Inputs from a 80 (or 85) C hot water and 4 C cold
> >water will be used to either heat or cool the structure.
>
> Are you removing water to compensate for the hot and cold water you're
> putting in? Or am I misinterpreting something?

Nope - - - its a water bath jacket where the water is in constant motion (always
being pumped. Any return water hits the return to the heating area - -
or cooling
area as needs be.
>
> Process is
> >monitored to +/- 0.2 C and I want to hold that T as closely as
> >possible to 1 C over recommended T - - - no more and no less (if I can
> >achieve +/- 0.5 C in the process i will consider moving to + 0.75 C
> >over recommended T. So its not exactly a simple control.
>
> Are you controlling the air temperature, or the temperature of the
> liquid in the vat? Or am I completely missing the picture?
>
Maybe - - - control of both the liquid in the vat AND the air above
the product
in the vat is required (as specified previously).

> Every temperature control system I've seen depended on hysteresis,
> which is hard to narrow down to less than a couple degrees Fahrenheit.
> I'm wondering if you should take a look at the algorithm from openntpd
> to see how they use a continually calculated drift number to prevent
> the need for sudden jumps.
>
Which is why one uses a pid control.
This kind of control is used routinely in certain areas of food processing so
its not a 'new' problem - - - I'm just not prepared to spend mega $$$$ on
the solutions generally offered - - - besides - - its an interesting problem
- - - grin!

HTH