• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 68 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.

ADS1232: Drift of full-bridge configuration

Bjorn Olsen
Prodigy 20 points
Part Number: ADS1232

Tool/software:

Hello,

I am using ADS1232IPWR with a full bridge configuration.

I am experiencing drift which is not related to temperature. 

Here are some further descriptions to my setup: 

  • Stable 5V, clean power supply to the bridge. The device is battery operated - not connected to mains
  • 10 SPS
  • 125 gain
  • No oversampling, no moving avergage etc. Just raw data offset with a calibration factor for grams.
  • I run the built in calibration - which should balance the bridge 
  • Constant temperature (I log it using a dedicated temperature chip on the board)

Attached is the design and drift results.

The total range of my scale is 200kg. The drift as shown is after ca 6min and is 60 grams. It is linear and just keeps increasing over time.
I require a long-term drift of less than 25g.

It is a reasonably simple design. 
What is the cause of this drift? Normally it is temperature - but here the temperature is 100% constant.
I suspect the bridge is not well balanced - but the build in calibration of ADS1232 should deal with that. And I do not really understand how a non-balanced bridge can cause this kind of drift.

Pleast help suggests how I can root-cause this.

Bridge power supply.pdf

  • 0
    TI__Mastermind 41380 points

    Hello Bjorn,

    Based on your description, I assume you are logging data with no weight on the scale, and expect the calculated value to be very close to 0g.

    Can you measure the voltage at both TP14 and TP17 with respect to ground using a DMM?  I want to confirm the common mode voltage of the bridge is near 2.5V (1/2 supply voltage).

    Also, if you short TP14 to TP17 with the bridge connected, then you should have an ideal 0V differential input with 2.5V common mode.  In this case, if you log data over time, do you still see the same amount of drift?

    If the drift is the ADC and not the bridge, then adding 1nF common mode capacitors to the CAP pins of the ADS1232 will usually help.

    Regards,
    Keith Nicholas
    Precision ADC Applications