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ADS1242: ADS1242

Eduard Dubinin
Prodigy 20 points

Part Number: ADS1242
Other Parts Discussed in Thread: ADS1231, ADS1220,

I am make a data acquisition from the devise,

the application is weight scale, with wheatstone bridge,

in steady state the data I am getting is pretty inaccurate, when using other ADC from another company the data is accurate,

The connection is as on following picture

The device configured:

PGA gain- 128

ACR register configured to:

U/B: 1

RANGE:1

maybe need to do some calibration ?

Thanks

  • 0
    TI__Guru** 113765 points

    Hi Eduard,

    From your schematic your are powering the bridge using 5V (and reference is also 5V) but your VDD supply is 3.3V.  Even if VDD is 3.3V you cannot use greater than 2.6V at range 1 for the reference input voltage as per datasheet.  So you are operating the ADC outside of specification.  I would suggest using a different ADC that has both analog and digital supply voltage input pins.  You might consider either the ADS1220 or the ADS1231 as alternate devices better suited for bridge measurements.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    Hi Bob,

    Thank you for the reply, sorry , there is mistakenly VDD is 3.3V in schematic, actually it is 5V  that connected via R283,

    and from datasheet using 5V reference and range 1  full scale for 5V can be applied,

    In my opinion in this case the device should be more precisely, or there is another points to check ?

    how I can do the results more accurate in steady state ?

    Which freq. T-filter should I apply ?

  • 0 in reply to Eduard Dubinin
    TI__Guru 58911 points

    Hi Eduard Dubinin,

    Bob is out of the office this week so I will offer my support while he is gone

    Can you tell me if the buffer is enabled for your measurements? With the buffer disabled, the ADC input impedance will be typically 39kohm at a gain of 128. This is rather low for a bridge measurement where the bridge impedance can be large e.g. 1kohm. This will result in an error

    With the buffer enabled, the analog input range is reduced to GND+0.05V and VDD-1.5V. What is the output voltage range of your bridge?

    Also, can you please define what you mean by "pretty inaccurate"? What accuracy do you expect to see, and what accuracy are you getting? The values you are showing in the first post (60607, 60918, etc.) - are those the decimal values you are receiving from the ADC when you are measuring the bridge?

    Finally, which ADC are you comparing to the ADS1242? Another 24-bit ADC? Even two 24-bit ADCs can have significant differences in performance, so it's not always fair to compare them without knowing more information. Let us know if you can provide a part number.

    -Bryan