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Data Loss in Continuous Conversion Mode with AD7177-2 Eval Software – How to Log Data Without Gaps?

Category: Software
Product Number: AD7177-2
Software Version: 3.3.2.3

I am working with the AD7177-2 in continuous conversion mode and using the AD7177-2 Evaluation software.
I have set the sampling mode to data logging and started sampling, but I am encountering data loss between
each conversion. I need to log data continuously for 30 minutes without any loss. How can I mitigate this
issue? Any suggestions or settings I should adjust?

Regards , 

Srihari

  • Hi  ,

    What ODR are you using and number of channels are enabled? Could you try setting the "Samples" to a value that all the enabled channels could completely convert for 1 second and see if this would work. This will force the Eval+ software to load samples for 1 second. We have seen this issue with the Eval+ software and there could be some processing time in the software where it could log all the data points at fast ODR. Try data logging for a shorter period to see if all samples can be captured.

    You may refer to the Virtual Eval | Analog Devices for the timing so you could calculate for the total number of conversions all channels can perform for 1 second.

    Regards,

    JC

  • Hi JC, 

    I have configured the ODR to 10,000 and set the "Samples" to 100 in the Eval+ software for the AD7177 ADC. In the attached image, you can see a sudden jump occurring every 100 samples. When I set the "Samples" to 10, a similar jump appears every 10 samples. I have enabled only one channel, and the ADC is configured for single-ended input with AIN1 set as common with setup0.

    Could anyone explain why this data loss is happening?



    Regards, 

    Srihari. 

  • Hi  ,

    It seems that your input is not constant/stable. Kindly try applying a constant voltage input and see if this sudden jump occurs. Please provide also your complete register settings so we could further debug the issue.

    Kindly clarify also what do you mean by 'data loss'? If you try zooming in the part where the sudden jump occurs, you should be able to see that samples are taken continuously.

    Regards,

    JC

  • Hi  ,

    When I apply a constant voltage, everything works fine. The problem arises with sudden jumps in the data. It seems like data is being missed every 100 samples when the Samples parameter in the software is set to 100. If I increase the Samples to 1000, I notice a sudden jump every 1000 samples, indicating data loss at those intervals.

    Register Settings:

    {"Generic":"AD7177-2","Registers":[{"Address":"0x0","Name":"AD717x:STATUS","Value":"0x0"},{"Address":"0x1","Name":"AD717x:ADCMODE","Value":"0x0"},{"Address":"0x2","Name":"AD717x:IFMODE","Value":"0x2"},{"Address":"0x3","Name":"AD717x:REGCHECK","Value":"0x0"},{"Address":"0x4","Name":"AD717x:DATA","Value":"0x90FC89FD"},{"Address":"0x6","Name":"AD717x:GPIOCON","Value":"0x800"},{"Address":"0x7","Name":"AD717x:ID","Value":"0x4FDE"},{"Address":"0x10","Name":"AD717x:CH0","Value":"0x8001"},{"Address":"0x11","Name":"AD717x:CH1","Value":"0x1"},{"Address":"0x12","Name":"AD717x:CH2","Value":"0x1"},{"Address":"0x13","Name":"AD717x:CH3","Value":"0x1"},{"Address":"0x20","Name":"AD717x:SETUPCON0","Value":"0x1B00"},{"Address":"0x21","Name":"AD717x:SETUPCON1","Value":"0x1320"},{"Address":"0x22","Name":"AD717x:SETUPCON2","Value":"0x1320"},{"Address":"0x23","Name":"AD717x:SETUPCON3","Value":"0x1320"},{"Address":"0x28","Name":"AD717x:FILTCON0","Value":"0x50A"},{"Address":"0x29","Name":"AD717x:FILTCON1","Value":"0x507"},{"Address":"0x2A","Name":"AD717x:FILTCON2","Value":"0x507"},{"Address":"0x2B","Name":"AD717x:FILTCON3","Value":"0x507"},{"Address":"0x30","Name":"AD717x:OFFSET0","Value":"0x800000"},{"Address":"0x31","Name":"AD717x:OFFSET1","Value":"0x800000"},{"Address":"0x32","Name":"AD717x:OFFSET2","Value":"0x800000"},{"Address":"0x33","Name":"AD717x:OFFSET3","Value":"0x800000"},{"Address":"0x38","Name":"AD717x:GAIN0","Value":"0x555210"},{"Address":"0x39","Name":"AD717x:GAIN1","Value":"0x555210"},{"Address":"0x3A","Name":"AD717x:GAIN2","Value":"0x555210"},{"Address":"0x3B","Name":"AD717x:GAIN3","Value":"0x555210"}]}

    Regards,
    Srihari

  • Hi  ,

    It is a limitation in the Eval+ Software wherein there is a bit of an added time delay for the software to output the set # of samples. If your input is rapidly increasing then your input may have increased already before the Eval+ Software starts to gather samples again.  I have replicated your setup on my end and the best results I could get is setting the number of samples to '1'. The reason is because setting the number of samples to '1' will give you a finer step change. 

    On another note, when a step change occurs on the analog input, the digital filters will need to settle on the new analog input. If the step-change in analog input occurs exactly at the start of a digital filter sampling period then the output code would have settled the third RDY pulse for sinc3 and fifth RDY pulse sinc5+sinc1. Each RDY pulse indicates the end of a conversion.

    However, a step change on the analog can occur at any point in the interval between two RDY pulses, so in general, the step-change will not occur at the start of the filter sampling period. This means the output code will not have settled by the third RDY pulse but will have settled by the fourth RDY pulse in the case of sinc3. Similar would happen for sinc5+sinc1, the output code will not have settled by the fifth RDY pulse but will have settled by the sixth RDY pulse. If the input is continuously changing then the digital filter would not be able to fully settle on a fixed voltage.

    You may also check the Virtual Eval | Analog Devices regarding the step response of the ADC.

    Regards,

    JC

  • Hi  ,

    Thank you for your response.

    Regards,

    Srihari:)