AnsweredAssumed Answered

ADC accuracy

Question asked by stabilo on Feb 20, 2018
Latest reply on Feb 21, 2018 by Lukas Zadrapa

Dear support team,

 

I use the ADC0 of the S32K144 to measure voltage (0 to 36V).

The ADC channel is configured to measure continuously at a sample rate of 5µs.  DMA transfer are triggered to transfer 32 ADC measurement into the buffer. Then, filtering and conversions are performed.

 

I have two problems:

  • The raw values into the buffer vary a lot (constant noise of ~ 15 digits)
  • The final voltage measured (filtered) is not accurate enough:

This picture shows the absolute error in function of the input voltage. Each point on the graph is a mean of 10 measurements (on these 10 measurement, the noise on measured values never exceed 5mV). As you can see, the error is very random (e.g. +40mV at 25.0V, -30mV at 26.0V).

 

I tried to enable the ADC self calibration, and the results are even worse.

 

Do you have any idea on how to improve my measurement accuracy ? (measurement rate ? reference voltage ? analog input capacitor ?)

 

I hope you can help,

Thank you very much.

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