--------
In message <[email protected]>, Bob kb8tq writes:
>If we want to hold the oven at some temperature +/- 0.1 C, the control loop
>needs to go from full on to full off over that range.
...ehhh, what ?
>You will map (somehow) the full range of the output into a 0.2 C input range.
Uhmm... no ?
The full DAC range maps to the heat you need for supply at the two
ambient temperature extremes.
For instance if you were building a -40...+70C OCXO, *ideally*
DAC code 0 should correspond to +70C and DAC code 65535 to -40C ambient
That means that one DAC step corresponds to a change in ambient temperature
of (+70 - -40) / 65536 = 1.7 milliKelvin.
A more realistic temperature range for a time-nut build would be +10...+40C.
DAC bits mK
--------------------
10 29.3
12 7.3
14 1.8
16 0.5
--------------------
10 bits would cause I-hunting in your PI(D) but the measurement noise
would probably dither that for you.
12 bits would allos a trivial implementation.
If you go for a double or tripple oven/dewar design, you probably
need 14 bits.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[email protected] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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