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ADS1220: Utilize 4 wire RTD PCB to measure 2 differential voltages

Christian Brunk
Prodigy 10 points
Part Number: ADS1220

Hi there,

I use the ADS1220 for 4- wire RDT measurement. My board has 24 x ADS1220 populated and I'm using a multiplexer for the SPI SS line to read out the temperatures sequentially. Everything is working well but now I also have to add 8 differential voltage measurements to this project. The voltages range from 8-22 mV.

At this stage, I'm trying to proof concept and have 8 extra blank 4-RTD PCB's from the manufacturer as I only had the choice to order 10 as a minimum quantity from the PCB supplier. If I can utilize these also for the voltage measurements in the meantime that would be great. I would do a proper PCB design later. The project is still at proof of concept stage. Can I just configure the ADS1220 to thermo couple settings and scratch the R3 lead wire track? I believe I still achieve reasonable resolution.

If the ADS1220 is suitable, is there a schematic/ circuit available for 2 differential measurements so I can cover 2 measurements with one ADS1220?

I'm trying to avoid having to use and learn about another chip as I'm already familiar with the ADS1220 and have a few spare chips.

Bellow is my current ADS1220 layout:

Thanks for your help!

Regards,

Christian     

  • 0
    TI__Guru** 113595 points

    Hi Christian,

    Welcome to the forum!  With your existing board you could use AIN0 and AIN1 as your input pair.  If you redesign, you could also use AIN2 and AIN3 as the second input pair. 

    It would be easiest to select the internal reference for the measurment. You could set the PGA to a gain of 64, however you must maintain proper common-mode for the input range being used.  This is discussed in the ADS1220 datasheet.  As far a specific design using two differential input measurements it is pretty straightforward.  It looks like what you have currently for the AIN0 and AIN1 inputs.  There are actually many combinations available based on MUX settings.  However, the best performance can be obtained by using AIN0 and AIN1 for one differential input and AIN2 and AIN3 for the second differential input.

    Best regards,

    Bob B