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ADS1247: SLAU520A - implementation

Geoff Kallweit
Prodigy 10 points

Part Number: ADS1247

Hello,

I have been following along with the Slau520a verified design for a 3-wire rtd circuit. The circuit makes sense to me but before I start trying to work with it, I wanted to see if there are any notes for testing or implementation. For instance, the 10 pin socket connector seems to have redundant i2c pins, and there is a 3-pin header that appears to be designed for a spdt switch between power sources. I'm curious how the circuit was interfaced and if there is any guidance available on testing/commissioning?

Thanks for any help.

  • 0
    TI__Guru** 100935 points
    Geoff,


    I don't know of any specific notes to go with the SLAU520A design for the 3-wire RTD circuit. I don't know where the header came from, but it might be something that we generically use for different platforms across our product line. That might account for the redundant I2C pins on header.

    I'm also not sure how the board was interfaced for testing. It's possible that we used the ADS1247EVM or ADS1248EVM to collect data since we're able to write registers and collect data with the software used for the evaluation module.

    I would note that I've run similar tests and I used precision resistors (low drift, high accuracy) as the RTD substitute. Most resistors were 0.01% or better with a drift of probably 5ppm/°C or better. When running tests like this, I measure back the test resistances using a four-wire Kelvin measurement with an Agilent 3458A. The accuracy is very good and the linearity of the resistance measurement is excellent. You should remember to keep the resistance measurement on the same scale (not auto-scaling) so that there are no discontinuities for changing the measurement range.

    It's important to realize that the design is written as if the circuit itself is always at room temperature. There will be added effects from offset and gain error drift from the ADC itself that I don't believe are considered.

    There is one last thing that I've been asked about in this design. In the schematic, the CLK pin is floating. It will probably be ok that way, but I always recommend tying the pin to ground.


    Joseph Wu