Hi
At least in my experience, a properly functioning OCXO will rarely (if ever) be
outside +/- 1 degree of the
set point when in full PID (integrator enabled) mode. You may well use a custom
set of control parameters
for the warmup phase. You might even use a non-PID based control (shut off all
power when these things
happen. Then coast to the set point …). I suppose that like many of my posts,
the term “fuzzy logic” could
easily be used in more than one way :)
Bob
> On Jun 10, 2017, at 3:10 PM, Magnus Danielson <mag...@rubidium.dyndns.org>
> wrote:
>
> Hi,
>
> Very good point Poul-Henning, very good point.
> The mux is there, we don't need the resolution far out, and with only a
> little though code-wise and hardware wise we get the best of resolution and
> range where we need it.
>
> Cheers,
> Magnus
>
> On 06/10/2017 09:06 PM, Poul-Henning Kamp wrote:
>> --------
>> In message <3897c09a-d76c-474c-8907-9ea25f8c3...@n1k.org>, Bob kb8tq writes:
>>
>>> The “limited range” part of it is why the op-amp makes so much
>>> sense. If the ADC can “see” +/-10C that’s way more than will ever be useful.
>>
>> Most uC's have a pile of mux'ed ADC inputs, so do all of the above:
>>
>> AI0 = Full range
>>
>> AI1 = +/- 10C
>>
>> AI2 = +/- 2C
>>
>> A big upside to this is that you will not need to invent heuristics
>> for clamped inputs in your PI(D) controller, something which is a bit
>> harder than most people realize.
>>
>> Assuming a 10-bit ADC, the code will look something like this:
>>
>> double
>> get_temp(void)
>> {
>>
>> T = read_AI2();
>> if (T > 50 && T < 975) {
>> T += T2_offset;
>> T *= T2_scale;
>> return (T);
>> }
>> T = read_AI1();
>> if (T > 50 && T < 975) {
>> T += T1_offset;
>> T *= T1_scale;
>> return (T);
>> }
>> T = read_AI0();
>> if (T > 50 && T < 975) {
>> T += T0_offset;
>> T *= T0_scale;
>> return (T);
>> }
>> abort("You have problems...");
>> }
>>
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