EVAL-CN0391-ARDZ - Temporal Resolution

Hi all, I want to use CN0391 board to measure temperature with 4 fine wire thermocouples and an Arduino board.

Which is the temporal resolution I can achieve? Would allow me to measure temperature change within ~20ms?

Regards

Carmelo

  • +1
    •  Analog Employees 
    on Mar 15, 2021 1:26 AM

    Hi Carmelo,

    CN0391 uses AD7124-8, an 8 channel 24-bit ADC with PGA. 

    At full power, it provide a sample of 19200 in a second which means that can take a single sample at the span of 52us per channel.  

    Using CN0391, you can measure temperature change within 20ms.  with this sampling rate of 19200 SPS,  you can get as much as 380 sample per channel in a period of 20ms. 

    Cheers,

    Erbe  

  • 0
    •  Analog Employees 
    on Mar 15, 2021 2:07 PM in reply to simoncelli

    There's a subtlety here - You can achieve 19200 sps if you're only looking at a single channel, but the filter has a settling time of 3 or 4 samples, depending on the filter selected. See page 55 in the datasheet for details, but this is also reflected in tables 8 to 37. "Output Data Rate" can be achieved on a single channel, but if you are measuring multiple channels (2 or more), use the "Zero Latency Mode" data rate, and divide by the number of channels.

    Since you want to measure 4 channels in 20ms, you'll need a zero latency data rate of 4/20ms = 200sps. From table 8, you could use the 320sps mode. At a gain of 32, this would give you a resolution of 0.38uVRMS. Divide this number by the sensitivity of your thermocouple, for example, for a type K thermocouple:

    0.38 µV / 0.41 µV/°C = 0.93 °C RMS temperature resolution.

    Of course this will vary slightly with the slope of the thermocouple at different temperatures, but not much. And also note that this ONLY considers the ADC input noise - it's unlikely that the thermocouple resistance will add noise, often environmental electrical noise will dominate, and that is something you will have to measure in your specific setting.

    -Mark

  • Dear Mark, thank you very much for your reply.... can you suggest any arduino code to print just the voltage of one channel at 20ms? I am struggling with that...voltage is enough for me, as I can work out temperature conversion in post analysis...I did the same using an IN-amp and works quite well, however, acquisitions are still quite noisy...I hope to use the EN-391 board to have acquisitions with reduced noise..thank you in advance....Carmelo

  • Dear Erbe, thank you very much for your reply.... can you suggest any arduino code to print just the voltage of one channel at 20ms? I am struggling with that...voltage is enough for me, as I can work out temperature conversion in post analysis...I did the same using an IN-amp and works quite well, however, acquisitions are still quite noisy...I hope to use the EN-391 board to have acquisitions with reduced noise..thank you in advance....Carmelo