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TDC1000: Some problems were encountered when using the TDC1000_TDC7200 scheme to measure the gas flow rate

tery shi
Prodigy 30 points
Part Number: TDC1000
Other Parts Discussed in Thread: TDC7200

I encountered some problems with the TDC1000_TDC7200 scheme when measuring the gas flow rate.  The use of TDC1000 TX1 and RX1 channel pair, TX1 transmitting pulse through the boost circuit to drive 78kHz ultrasonic transducer, through the oscilloscope to see TX end transmitting pulse after the up and down oscillation will last for a long time, do not know why?  The transducer of RX end is 17cm away from the TX end. Through the oscilloscope, we can see that the received sound wave is very weak. When the transducer is connected to the RX end of TDC1000, we can't see it. 

  • +1
    TI__Mastermind 23045 points

    Hello Tery,

    Thanks for posting to the sensing forum! The time it takes the signal to come down after pulse has been emitted is known as the ringing period. It takes time for the TX transducer to stop ringing once it has been excited. This is the purpose of using two transducers for very close measurements due to this ringing period.

    The signal received is typically small, are you probing the transducer directly or are you allowing to go through some of the gain stages first before probing? If you probe the COMPIN part of the circuit it should allow you to see the filtered and amplified signal a whole lot better.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 30 points

    Because 78kHz transducer is used, I modified the following circuit according to the manual, and also set the gain and filter, but I could not see the echo signal in COMPIN, like the interference was amplified. 

    Could you give me some suggestions on the modification of the gain and filter circuit?

  • 0 in reply to Isaac Lara
    Prodigy 30 points

    This is the waveform measured by COMPIN. 

  • 0 in reply to tery shi
    TI__Mastermind 23045 points

    Hello Tery,

    As mentioned in a previous conversation this device is not recommended for usage under 1MHz. Typically due to the dynamic range needed for lower frequencies, this is not available in TDC1000 since it only has 21dB of available gain but it may work in this scenario since the spacing between the transducers is relatively small. You can try the values from this board these were from an old TDC1000-GASEVM we used to sell online the filters are configured to work with 58kHz to 300kHz transducers 

    I think you should also check your values for the listening window to ensure that your device is listening at the appropriate time as well.

    Best,

    Isaac

  • +1 in reply to Isaac Lara
    Prodigy 30 points

    Well, thanks for the advice.