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Original question:

IWR1443: Water level measurement and resolution

IWR1443: TIDEP-0091 range resolution and accuracy

Christopher Steines
Prodigy 20 points
Part Number: IWR1443
Other Parts Discussed in Thread: TIDEP-0091,

I've been trying to scour the forums to get a better understanding of the range resolution and accuracy of the TIDEP-0091 demo program out of the box.  I am attempting to us the IWR1443 to measure fluid level in an range of tank sizes, starting with 55 gallon drums and increasing from there.  In test with a 55 gallon drum, I'm getting strangely repetitive measurements from the TIDEP-0091 setup.

For example, with the barrel filled with water so that the surface sits 17 inches from the surface of the IWR1443Boost board, the demo device is outputting 0.488641m, 0.451053m, and 0.526229m.  When I raise the fluid level by 1 inch, I receive the same measurements from the device.  This repetitive nature in values is seen across the range of fluid levels, causing me to question if the range accuracy of the demo configuration is equal to the range resolution of 3.75cm.

Please correct me if I am wrong, but I understand the base range resolution is limited to the 3.75cm due to the 4GHz range of the chirp frequency.  I have read through several related threads and have come to the understanding that the range accuracy is a function of the SNR, range resolution, and FFT size.  Is a range accuracy of the base demo of 3.75cm to be expected without performing a zoom FFT?

Is there a demo project available yet that incorporates the zoom FFT into the low power fluid level sensor?  The only zoom FFT project that I have found is based on the old SDK, so making the conversion is a bit over my head, and more time consuming that I can currently invest in this project.

For this particular project, an accuracy of 0.5 inches would be ideal.  Any suggestions of how to achieve this would be much appreciated.

Thanks,
Chris

  • 0
    TI__Guru 50240 points
    Hi Chris,

    Thank you for your question. Have you seen the Chirp Budget Calc spreadsheet in the TIDEP-0091? (it is located near the bottom of the webpage).

    There are four different configurations illustrated in the spreadsheet, each one with maximum distance and relative range resolution. You can also try to configure the parameters yourself. They are located in the demo.h file (15 m config used as a default, 30 m config included as a # define).

    The TIDEP-0091 does not yet incorporate the zoom-fft, we are looking into it but cannot provide an estimate at this time.


    Let me know if you have more questions.


    Cheers,
    Akash
  • 0 in reply to Akash Gondalia
    Prodigy 20 points
    Hi Akash,

    Thank you for the reply. I did find the excel spreadsheet in my search and attempted playing around with the configuration based on the values I modifed in that file. Whenever I have made any modifications to reduce the range resolution, I receive a MMWave_Config error in the uart interface when I try to take a single measurement. Based on what I've read in the other resolution/accuracy threads, the 3.75cm seems to be a theoretical physical limitation due to the chirp frequency spread (Am I incorrect in this understanding?).

    Aside from the value requirements specified in the excel spreadsheet (like "needs to be an integer * .001Mhz"), are there any other maximum and minimum limitations for items like the DFE Outrate or SynthSlope values? Those two items seem to have the greatest impact of the range resolution, and whenever I have modified them, I receive the config error.

    I also find it peculiar that if the accuracy is finer than the 3.75cm resolution, every value I receive is a multiple of 3.75cm aways from the others. I do understand that the resolution would cause the sensor to only detect reflections that are 3.75cm away from each other, but it doesn't mean the initial reflection detected will always be a multiple of 3.75cm from previous test cases. Hopefully I am explaining my confusion and understanding correctly.

    Thank you in advance for your continued assistance,
    Chris
  • 0 in reply to Christopher Steines
    TI__Guru 50240 points
    Hi Chris,

    Have you tried working with the mmWave Sensing estimator? dev.ti.com/.../

    This is going to be a helpful tool for seeing how various chirp parameters are affected by your desired performance.

    You are correct that range resolution is capped at 3.75 cm. For the TIDEP-0091, accuracy is slightly better which is why you are seeing your measurements like this.


    Cheers,
    Akash
  • 0 in reply to Christopher Steines
    Prodigy 110 points

    Christopher, I too noticed the literature saying there is a 4cm max resolution.  I have a client that that used a competing solution with a very wide FFT and got closer 1 mm accuracy (but without being able to read angle or Doppler shift) - but this was with a very limited range and after a lot of tweaking of Tx and Rx parameters.  I noticed the TI examples seem to be for a large range - I have hopes the TI part can be configured to work with near range and good accuracy.