• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 531 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1246 Calibration

Stephen Power
Intellectual 405 points
Other Parts Discussed in Thread: ADS1246

Hi

I am considering using the ADS1246 for a new thermocouple design. Calibration of this new product will be infrequent and I would like to maintain accuracy as much as possible over temperature and time. The ADS1246 datasheet says that it has 3 calibration modes: system gain calibration, system offset calibration and self offset calibration. I am unable to use the system calibrations as there will be no external reference available. Thus it seems that the only calibration that could be performed with temperature or time changes is self-offset calibration.


A competing product is the AD7793 from Analog Devices. This part states that it has 4 calibration modes, the 3 mentioned above and also internal Full-scale calibration. With this part it appears that I can do both offset and gain calibration at any temperature or time. This is quite appealing for my particular application. However, there are features of the ADS1246 that also appeal to me, including higher sample rate.

The AD7793 datasheet does not contain a lot of information about how internal Full-scale is performed across all gains. I am wondering whether TI has anything to say about this feature and why, for example, the ADS1246/7/8 does not include it? Perhaps it is not very accurate? Can you provide any advice on this matter?

I would be happy to continue the discussion off post.

regards

Steve

  • 0
    TI__Guru* 94335 points
    Steve,


    I think the AD7793's internal full-scale calibration is similar to a self gain calibration that we have used in several of our other devices. In this case, the ADC takes the reference as an input which is considered as full scale and compares it against the same reference.

    From a circuit standpoint, it's just making sure that the sampling of the reference and sampling of the reference are correlated so that the full scale measurement will give an output of 7FFFFFh. It's not an uncommon command. It's making a fine adjustment to the FSC register (as shown in figure 66 of the ADS1246 datasheet). For the AD7793, you can run a calibration to make a fine adjustment for each gain setting.

    For the ADS1246 however, we program in the FSC register for each particular gain setting. If you change the gain, it will enter in a new value for the FSC register that we tested for each device (and programmed in for each gain). In the end, we feel that this method gives a good result for the gain accuracy instead of running a gain calibration.


    Joseph Wu