• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 30 subscribers
  • Views 675 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TDC1000: Echo signal period variation

Lawrence Lee
Prodigy 30 points
Part Number: TDC1000
Other Parts Discussed in Thread: TDC7200,

The TOF we get from TDC7200 include two parts . One is TOF in measured fluid and the other is the period between start point of echo and zero cross point.

For example if the zero cross point on the second pulse, we need to deduct double period of echo signal to get TOF in fluid.

Originally we think Ultrasonic speed vary if temperature or concentration changes. Frequency and period of echo signal are not affected by temp and concentration.

However , we find echo period is also changed and the variation can't be measured exactly. 

This cause that we can't get exact TOF in fluid to calculate speed for a fixed distance. Is there any idea to fix it ? Thanks.

  • 0
    TI__Mastermind 21685 points
    It's important the transducer is excited by TX pulses whose frequency matches the resonant frequency of the transducer. Please check the transducer specifications to make sure you are exciting with the correct resonant frequency. Also, double check TDC1000 settings and clock input to derive the TDC1000 TX frequency.
    Are you using TDC1000-TDC7200EVM? What's your setup looks like? What's the resonant frequency of the transducer you are using?

    Thanks,
    Vishy
  • 0 in reply to Vishy Viswanathan
    Prodigy 30 points

    The input clock is 8M Hz. The resonant frequency of the transducer is 1M Hz.

    The setup of TDC1000 is as below.

    TDC1000_reg_data[10] = {0x45, 0x41, 0x00, 0x06, 0x1F, 0xE3, 0xFF, 0x00, 0x1B, 0x01};

    We use our own board which is based on EVM.  Do you need to check the circuit ?

    I think TX pulse frequency matches the resonant frequency of the transducer in our design.

    Any other possible cause ?

  • 0 in reply to Lawrence Lee
    TI__Mastermind 21685 points
    Lawrence,

    I reviewed the register settings. There are a few things you need to change
    a) Since you are using Mode 0, I assume you are using a single transducer to send on TX1 and receive on RX2. TX1 and RX2 should be connected together as shown in the EVM schematic and the transducer should be connected between TX1/RX2 and GND. I assume this transducer is properly mounted with no air gaps on the surface of the container with a proper adhesive that conducts ultrasonic energy without loss. You can refer the following app notes on transducer mounting and level measurement
    www.ti.com/.../snaa266
    www.ti.com/.../snaa270

    b) For level measurement, it's better to use "Multi Echo" receive mode in CONFIG4 register. Single Echo mode is for flow and you can read about singe and multi echo modes in the TDC1000 AFE device data sheet.
    www.ti.com/.../tdc1000

    c) You should reduce the PGA Gain (currently set at maximum 21dB) and also the echo qual threshold (currently set at 775mv) so you have a good headroom to make sure the system operates through all conditions.

    d) The echo timeout is enabled and set at 128us. So make sure your expected time of flight is less than this period. Otherwise TDC1000 will timeout before that.

    e) It would be helpful to review how you have connected TDC1000 and TDC7200 pins. If you can share just that part of the circuitry (with transducer connection) we can make sure there's no issue on that. Also, if you have an TDC1000-TDC7200EVM, it's good to experiment with that to make sure everything is working. The EVM has opamp buffer on the COMPIN pin, so you can observe the START, STOP and COMPPIN pins to see how good is the echo with the setup and optimize it as discussed in the app notes I refer above.

    Thanks,
    Vishy