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ADS1147: SELFOCAL command

Max Tibbetts
Prodigy 170 points
Other Parts Discussed in Thread: ADS1147

Hi all,

I have some confusion about understanding the SELFOCAL command for the ADS1147. I know it acts like a background calibration, but I am not sure whether it overwrites the OFC registers or adds a value to them.

I am using a ratiometric approach for calculating the temperature as well as using a two-point calibration scheme to calculate my offsets. In addition, I am using a lookup table that corresponds each hexadecimal codes to a specific temperature. Finally, I am using a 4-wire RTD configuration.

  • 0
    TI__Guru** 113765 points

    Hi Max,

    The SELFOCAL command applies an internal short and adjusts the OFC registers accordingly (writes a new value).  Any reference noise will affect the result as it is an average of several readings.  The SELFOCAL only applies to the PGA and conversion process.  Any external offset will not be included.

    One thing you can do to remove offset is to take more than one measurement. The first measurement will be your normal reading.  The next measurement you swap the mux channels to reverse the + and - input selections.  Average the two measurements and you should eliminate the offset.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 170 points

    Thanks Bob,

    In general, which method is better for calibrating, a SELFOCAL before every measurement or a manual two-point calibration? 

    Max

  • 0 in reply to Max Tibbetts
    TI__Guru** 113765 points

    Hi Max,

    Both methods should give similar results.  If not, then there is a noise source contributing to the difference.

    Best regards,

    Bob B