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MSP430FR5043: Tprop definition and usage

Hideki Hayashi1
Expert 7600 points
Part Number: MSP430FR5043

Tool/software:

Hi team,

I had technical QAs with Cash in email, but I need your help here due to his paternity leave.

I asked and Cash answered below. 

[Hayashi] In the Application Report “Waveform Capture Based Ultrasonic Sensing Water Flow Metering Technology (SLAA889A),” Tprop (propagation time) appears and is used in Equation 13.

It also states that it is set by #define USS_ACOUSTIC_LENGTH in the USS_userConfig.h file.

However, customer have measured the ultrasonic propagation time and instantaneous flow rate by changing the settings in USS_ACOUSTIC_LENGTH, but did not see any change in the output values. can you please let customer know how to define or edit Tprop?

[Cash] Tprop is now used as the ADC start capture delay. It is not related to the USS_ACOUSTIC_LENGTH. Customer can consider the Tprop as USS_START_CAPTURE_SEC now.

Customer have additonal question.

1. Does Equation 13 mean Tups = Tupscorr - Toffset, is it correct?

2. Is Tprop same as Gap between pulse start and ADC capture, which is in Ultrasonic Sensing Design Center? If yes, how is the value of USS_START_CAPTURE_SEC, which sets the Trop, and the value of ‘Gap between pulse start and ADC capture’ used differently?

Best regards,

Hayashi

  • 0
    TI__Genius 13440 points

    Hi Hayashi,

    The Tprop value shown in equation 13 lists the time for the signal to propagate from the microcontroller's output to the input. Cash's more recent comment may mean that the ACOUSTIC_LENGTH define is no longer used by the USS algorithm, and the customer's observation seems in line with that. He mentions using USS_START_CAPTURE_SEC instead, so I would encourage you to try using this for the Tprop value in the application. The ADC start capture delay is defined as USS_ADC_SAMP_COUNT_SEC though. In my view, the start ADC capture define shouldn't be used as the Tprop value as the ADC capture begins slightly before the waveform has propagated to the ADC.

    To answer your direct questions:

    1) No, it means Tups = Tprop + Tupscorr -Toffset. Tups indicates the total flight time of the upstream signal

    2) Tprop is close to the gap between pulse start and ADC capture. If you take a look at the example ADC captures given in our docs, such as the USS academy, you can see the ADC capture includes a small amount of time where the captured signal is flat, before the excitation pulses arrive. That time is the difference between Tprop and the gap between pulse start and ADC capture. 

    Maybe I could assist more if I knew what the customer is trying to accomplish. As long as the gap between pulse start and ADC capture is set correctly, the algorithm should be able to detect the beginning of the pulses, and thusly is able to calculate the absolute time of flight.

  • 0 in reply to Dylan OBrien
    TI__Expert 7600 points

    H Dylan,

    Your explanation were clear, thank you! Let me double check customer's understanding

    Dylan OBrien said:
    Maybe I could assist more if I knew what the customer is trying to accomplish. As long as the gap between pulse start and ADC capture is set correctly, the algorithm should be able to detect the beginning of the pulses, and thusly is able to calculate the absolute time of flight.

    Customer wants to use it for water metering, and need to find best values on each parameters for flow paths and sensors.

    There are so many parameters that customer are struggling to understand what each parameter means and to find the optimum values.

    Based on what you have answered, customer have created a timing diagram to the best of our understanding. Could you please check if it is correct? If there are any mistakes, please point them out.

    timing_picture.pdf

    Regards,

    Hayashi

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