From: Spehro Pefhany
Subject: Re: Rollover error
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Date: Fri, 03 Jan 2003 05:44:38 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 00:44:38 EST
On Fri, 03 Jan 2003 05:19:29 GMT, the renowned "Tom Del Rosso"
>"Spehro Pefhany" wrote in
>> >What is the meaning of rollover error in A/D convertion?
>> Apply about full scale input, swap polarity, measure the difference
>> between the magnitude of the readings.
>One time, when the battery was low in my Fluke 77, I would get wildly
>different values by reversing a DC measurement. Was that because of
>rollover error increased by the low battery, or simply the voltage
>reference going off-center? (Or is that the same thing?)
Probably the integrator was saturating.
The dv/dt at the integrator output is a function of input voltage,
the time is fixed, and you want to keep the swing reasonably large,
but if the supply voltage decreases, there will be a collision, and it
will probably happen in one polarity before the other.
The rollover error we're talking about here is something different-
the capacitor has a "memory" of previous charge, so the +ve and -ve
readings are different for a lousy capacitor and close to the same for
a good capacitor.
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