On 3/30/2010 6:29 PM, ivp wrote:
> Hi all,
>
> Help
>
> Cure suggestions please ?
>
> TIA
>

It looks like your RPM sensor has an offset voltage.  If this is the 
case, try this:

a) A pot (say 10K) from +5 to ground.
b) A 510K resistor from the wiper to the negative input of the amp.

This should give around +/-100mV of offset adjustment.
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