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TUSS4440: Improving minimum distance w/ monostatic configuration

Dan Munro
Prodigy 10 points
Part Number: TUSS4440

I am working on a prototype using the TUSS4440 sensor paired with a Pro-wave 235kHz transducer (xfrmr driven using a fixed Wurth xfrmr). When I test this transducer and transformer with the EVM I get excellent minimum distance performance ~2-3inches from the sensor face. With my board layout using the same parts, I see a minimum sensing distance of 4-6inches, which is a problem for my application.

What steps can I take to improve minimum sensing distance and why do you think I am seeing this difference? I am using the same tuning network / xfrmr / xducer / parameters etc.

  • 0
    TI__Mastermind 23045 points

    Hello Dan,

    Thanks for posting to the sensing forum! My first thought is actually that the difference in your minimum measurement is due to the different transformer in your current implementation. We have seen quite a difference in ringing decay profiles from different transformers, I am not sure if the package is the same but have you tried replacing the transformer with the transformer found in the EVM (Coilcraft WA8351-AL) to see if it provides any improvement?

    I would mainly take a look at the the  tuning network in your system, since the tuning network is used to match the driving frequency of the transducer and reducing the ringing decay time these components are selected based on the transformer. Since there is a difference in the two passive components found in your board and the EVM this can most likely cause a change in what the ideal tuning components would be. The tuning components found in the EVM might not be ideal for your system, my recommendation would be to check the values in this network mainly the damping resistor.

    We currently do have a nice way to check what is the most ideal resistor but our suggestions is to sweep a potentiometer and test to see where you get an ideal decay time. This app note contains some more info under section 4.4: www.ti.com/.../slaa732a.pdf

    Best,

    Isaac

  • 0
    Prodigy 10 points

    Hi Isaac,

    I modified the EVM to utilize the same transformer that I have on my design and removed the RC matching network on the EVM so I can assemble my RC network at the back of my xducer. Yes, I have tuned the damping resistor with a potentiometer and found the optimal value to be 650-900ohms. Capacitor was empirically tuned to 2nF. I have the c_flt selected to be 3.3nF on the EVM and matched this on my board. Any other ideas on what might be causing this?

    Do you have any references for manufacturers of variable inductance transformers? It seems this could be another avenue for improving minimum sensing distance

  • 0 in reply to Dan Munro
    TI__Mastermind 23045 points

    Hello Dan,

    Thanks for the info, this part wasnt inherently clear to me but when you replaced the Wurth transformer on the TUSS4440EVM did you see a similar decay time as with you did with your custom board? Or was the decay still ~2-3 inches as seen with the Coilcraft transformer?

    If the EVM was pretty consistent across the two transformers my next thought would be a schematic review and perhaps a layout review just to ensure we don't see anything odd. If you do not feel comfortable sharing on the forum since it is public, feel free to send it via a private message.

    But yes variable inductance transformers can be used to reduce the decay time, we have a list of some transducers and transformers listed here: https://www.ti.com/lit/zip/slac787

    Best,

    Isaac