> Tom Handley wrote:
> [snip]
> > In my design, I wanted a range from 28 to 32 InHg and a resolution of
> > 0.01 InHg. This required an A/D that could resolve 400 steps and would
> > require a typical 10-Bit A/D but I already had an 8-channel, 12-Bit A/D
> > (MAX186), in my design with a resolution of 1mV/step. I selected the
> Sensym
> > SCX15ANC transducer....
>
        Wagner replied:

> ... if the full scale is 32 InHg and the resolution is 0.01 InHg, it
> will demand 3,200 x 0.01 InHg to go to full scale, so 400 steps is not
> enough, 4096 is, so the 12 bit a/d.  By my experience, all the
> calculations, scale corrections and temperature linearity math requires
> a better a/d resolution, to give you the required slack to deal with
> math fractions and rounding.
>
        <snip>

But he wants to start at 28 InHg i.e. the sensor/signal conditioning is
arranged so that 28 InHg gives an input of zero volts to the ADC.  (32-28) /
0.01 = 400.  Just under 9 bits are needed for the resolution Tom requires,
obviously not a commonly available device :o)

Regards

Mike Rigby-Jones