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TDC1000-TDC7200EVM: Using EVM for other transducers

Deepti Salunke
Prodigy 90 points

Part Number: TDC1000-TDC7200EVM

Hi,

Can I use this EVM with transducers having frequency 40 kHz? do TDC1000 support 40 kHz transducers?

  • 0
    TI__Genius 17440 points

    Hi Deepti,

    The TDC1000 will support 40 kHz transducers. The device's output frequency is determined by the input clock frequency and the user-controlled clock divider. The clock division factors are powers of two ranging from 2 to 256. The minimum input clock frequency is 60 kHz, and using the maximum clock division factor 256 yields an absolute minimum output frequency of (60 kHz)/256 = 234.375 Hz. 

    Regards, 

  • 0 in reply to Kristin Jones93
    Prodigy 90 points
    Hi Kristin,
    Thanks for the reply. It was helpful.
    I brought theTDC1000_7200EVM. I am using it for air speed measurement. The range I'm looking for the measurement is 0-60 m/s with the accuracy of 0.3 m/s. Am I using correct frequency of transducers? distatnce between two transducer will be 18-25 cm.
  • 0 in reply to Deepti Salunke
    TI__Genius 17440 points

    Hi Deepti,

    The accuracy of your measurements will not be affected by the transducer frequency you use. It is limited by the TDC7200's 55ps resolution, which is much smaller than you need for your application. I did some math using this flow-metering application note, and assuming your delta time-of-flight is the TDC7200's minimum resolution and your transducers are spaced 20cm apart, you should have a speed resolution of less than 1 mm/s. The transducer frequency you've selected is a good choice for air-coupled applications. 

    I would also recommend using the TDC1000-GASEVM, which also uses the TDC7200, but the passives are tuned for frequencies between 58 kHz to 300 kHz instead of the higher frequencies used for liquid-coupled applications. It also uses higher voltages to stimulate the transducers, which can be needed in air-coupled applications. This EVM is typically used for flow-metering in pipes. I'm not sure what shape your test chamber is, but you would need to make sure your air flow is laminar for the time-of-flight calculations to be accurate. 

    Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 90 points

    Hi Kristin,

    You are correct. I am getting the accuracy more than I expect to.

    I have seen the difference between TDC1000-GASEVM and TDC1000-7200EVM. I want to ask if I make following changes to the existing board, will it do?

    1. Removing R41 and R42

    2. Replacing C42 and C43 with resistors so as to have resistive feedback

    3. Replacing components of filter between COMPIN and PGAOUT so as to work with 40kHz center frequency

    4. Replacing C36 with another value. (pls suggest the value for 40kHz)

    5. Adding TDC100-BSTEVM so as to boost the voltage. (can I buy BSTEVM separately or have to make my own PCB?)

    I am using transducers in the open air. There is no chamber as such. I don't think it is laminar air flow. My application needs it in the open air only.

  • 0 in reply to Deepti Salunke
    TI__Genius 17440 points
    Hi Deepti,

    I do not think it would be worthwhile to try to change the TDC1000-TDC7200EVM into the TDC1000-GASEVM. The BSTEVM can only be purchased as a bundle with the TDC1000-GASEVM, so you would not need to change the TDC1000-TDC7200EVM. In addition, our TDC1000 expert has advised me that the TDC1000-GASEVM has a bandpass filter that will remove signals under 58kHz, so I would recommend using a transducer of at least this frequency.

    If your application is open air, you may need to consider using more than two transducers. We have not worked on air speed measurement directly, but we have worked with one other customer who used the TDC1000-GASEVM for this application. They encountered some time-of-flight calculation errors, possibly due to air turbulence or air blowing at an angle compared to the transducers' trajectory. I believe they ended up needing to use four transducers to account for Doppler shift. Their target resolution was 0.1m/s, so you may encounter similar problems. However, if you know your air flow will only be in one direction, two transducers should suffice.

    Regards,