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AD7730 different AD Values at startup

Question asked by Eize on Nov 16, 2015
Latest reply on Dec 1, 2015 by JellenieR

We had some difficulties with a AD7730.

After startup, the AD value is not consistent, once it start with 1,8 * 10^6 and the other time with 1.9 * 10^6.

In the attachment a picture of this behavior ("Different Zero Points.pdf").

We've set up this test with an automatic test-program. The microcontroller resets themself after a period of time.

These are the spikes down to zero.

 

The AD converter is setup with a interal full calibration and internal zero scale calibration.


The AD conversion is measured in UNIPOLAR mode with a range of 0-20mV with the DAC on +2.5mV.

It occurs with Ch0 of the AD7730, so the input with AIN1+ and AIN1-

 

The input filter between AIN1+ and AIN1- had recently changed.

Old type: see attachment: "Old filter.jpg"

New Type: see attachment: "New Filter.jpg"

 

The problem occurs with the Old type off the filter. With the new type we've seen no problems.

 

Does anyone recognize the described problems?

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