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RE: ADS1230 Temperature Drift

SUCHITRA BHIDE
Prodigy 230 points
Other Parts Discussed in Thread: ADS1230

Hi 

Have you tried taking readings with temperature changes.?

I am trying to develop a similar application but I am not getting the desired accuracy. My bigger worry is when I am shorting both the inputs of ADS1230 to ground I am getting high offset of 0x894 and this keeps on changing. Is this a device issue or my board is having a lot of noise?

How do I fix this. Secondly when I connect the load cell I am getting a negative readings of 0xFD1E at no load. I am expecting the load cell to be fully balanced. meaning at no load it should give me a reading same as the offset. 

Secondly I am seeing a lot of variation with temperature. The offset varies with temperature

How do i fix this issue.

kind regards

Suchitra

Pin voltages I am using are as follows:-

DVDD = REFP = 3.3V (generated by using TPS71533)

GAIN = 128 

SPEED 80SPS

 

  • 0
    TI__Guru** 113765 points

    Hi Suchitra,

    It is always best to create a new post instead of posting on another that is a year old and has a different topic.  There are a number of things to consider.  First I'll discuss the shorted input case.  When shorting the inputs you cannot short them to ground as you will be outside the common mode input range of the ADS1230.  This is shown on page 3 of the datasheet near the top of the page.  AINP and AINN when referenced to ground must be less that AVDD-1.5 and greater than AGND+1.5V.  Shorting these to ground is a problem as it is outside of this range.  The best method is to short the inputs together and bias them to AVDD/2.

    The next thing to consider is whether you are conducting the self offset calibration procedure discussed on page 16 of the datasheet.  This is initiated by sending two more clocks after the data is read (26 clocks).  This method will remove offset of the ADC and PGA of the ADS1230.  This calibration should always be done at power up and periodically or in conditions where you suspect temperature to be changing.

    Load cells and bridges are never truly balanced at the start.  So you have to adjust your result accordingly.  In your case you are showing a negative offset.  I'm not sure if this is offset of the ADC (did you run the offset calibration?) or if it is the offset of the load cell or some other factor or combination of factors.  If you have run the offset calibration and there are no other causes outside of the load cell, then when it comes to offset of the load cell you need to subtract the offset (which as a negative value in this case is subtracting a negative value and ends up as an add) of the no load result to your final value.  The result will then be 0 for the no load condition.

    Another condition that will cause temperature drift issues is with respect to components used in your input system.  You need to make sure that component drift is not creating a differential voltage.  This can be caused by unbalanced filters at the analog inputs. Common mode caps must be less than 1/10 the value of the differential cap.

    If you send me your schematic and layout I can further help identify potential problems.

    Best regards,

    Bob