Re: LM34 to A/D



Anthony Fremont wrote:
Fred Bloggs wrote:

John Larkin wrote:


Actually, unless you want to spring for 0.1% resistors, the gain
stage will probably make accuracy worse.

If the LM34 is connected directly to the ADC, inserting an R-C
lowpass is still a good idea. ADC mux's commonly kick out spikes,
and the LM34 series has a weak pulldown and lots of quirks.

The gain makes the difference between induced noise on the board
amounting to several degrees or a fraction of a degree. The input
range of interest is 50-120 oF or 0.7V so a gain to full range of the
ADC is approximately x14. This means the ADC will see 140mV/oF versus
10mV/oF, making reasonable amounts of onboard noise equivalent to a
fraction of a degree versus several whole degrees.


You seem to be making the assumption that the noise would only be introduced _after_ the op-amp.



pleeze...

.

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