ADT7410 noise/effective resolution

I have 8pcs of ADT7410 sensors connected to a PIC18F47J53 microcontroller via 2 individual I2C interfaces running from 2x AA batteries. Each sensor has a 4.7µF ceramic decoupling capacitor soldered as close to the sensor as possible. The sensors are configured to "normal mode" at 16-bit resolution. The sensors are placed close to each other (the distance between them is not more than 20mm) - the temperature-wise steady environment is ensured, verified by a laboratory reference thermometer.

With this setup, 1024 consecutive measurement points are taken per each sensor and analyzed - see attached file with the results. The top chart shows all the measurands [temperature vs. time] (the blue lines indicate the maximum and the minimum values), the bottom-left chart is the output of the Fourier-Transform (which shows no periodicity in the signal), the bottom-right chart is the histogram of the readings.

The histograms are showing a bimodal and/or skewed distribution – it’s not white noise. Also, the difference between the maximum and minimum values of 1024 readings is around/above 0.1°C. These findings lead me to a conclusion, that the advertised 16-bit resolution (0.0078 °C) is not achieved (i.e. effectively, the resolution is 13-bit, even if the sensor is configured to 16-bit!). Is this the best signal-to-noise ratio, that this sensor can do - or am I missing something important?

Insight of experts would be appreciated.

Regards,
Balázs

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  • 0
    •  Analog Employees 
    on Apr 23, 2020 8:01 AM

    Hi, Balazs.

    The ADT7410 is a 0.5C accurate part that can be configured for both 16-bit and 13-bit resolution, referring to how many codes the internal ADC can resolve. Because of input referred noise in ADCs, you are only seeing about 11- or 12- bit of noise free (flicker free) code resolution. You can improve the resolution by implementing a rolling average filter. Please see the attached sample file for an illustration of this. You can also read more about ADC input noise and noise free resolution in this Analog Dialogue article.

     XLSX

    Hope this helps.

    Regards,

    Karen