Re: LM34 to A/D



John Larkin wrote:
On Fri, 31 Aug 2007 12:44:09 -0400, Fred Bloggs <nospam@xxxxxxxxxx>
wrote:

But you could oversample and average. Temperature changes slowly, and
code is cheap.

John


I don't, and will never, trust averaging an acquisition synchronized to a digital clock.



These days, it's hard to make any other kind of acquisition. I almost
always software lowpass filter stuff like this, slow things like
temperature acquired by a fast sampling ADC. There's usually enough
natural noise floating around to dither a 12-bit system up to 14 or
even 16 bits of usable resolution. And if there's a high temp shutdown
or something like that, filtering avoids false alarms from spikes or
whatever.



Use the cheap code to correct for gain and offset of the cheap gain amp, which can be calibrated with a cheap voltage input.



He can calibrate based on a temperature standard, in the extreme. We
don't know if he wants to store custom cal factors per system.

John


Since the temperature uncertainty of the '34 is adequate he does not need a temperature calibration. He can use E96 metal film resistors for his gain and bias setup of the gain amp and calibrate those errors with a simple voltage input. The E96 metal film should track in ratio at 5ppm/oC so I don't see reasonable operating environments being a problem.

.

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