Q
We have used the AD7730L for some years now and are using the converter in
chop mode, which gives us some problems with the frequences going through
around the sampling frequence, so my question is: Our weighing cycle is 2-3
seconds but we only need the A/D values for a short period of the 2 seconds,
about 0,2 seconds. It is possible to avoid the drift if we run 1,8 s with
chopping and 0,2 s without chopping. Will this be a better solution
regarding drift than if you do not use chopping at all?
A
Using the AD7730 in chop mode effectively elliminates the internal offset from
the AD7730, by switching to non-chop mode, the result will be different from
chop mode as the offset that has increased with drift will now be included in
the result.
When you calibrate the AD7730 periodically for zero scale offset you
effectively achieve the same result as using the part in chop mode -
therefore, as you have sufficient time to calibrate between conversions, I
would suggest to operate the device in non-chop mode and perform an internal
zero scale calibration between conversions to elliminate the offset introduced
by drift.