MSP430FR5043: Tprop definition and usage

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.

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

Your image shown in the attached pdf looks good to me.

We do have additional documentation providing info on which physical values are determined by which defines and variables, shown in the following links:

1) USS Design Center Users Guide

2) MSP430FR6043 Application SW Guide

3) MSP430 USS API Guide

However I do wonder if maybe this is too much information and may become more confusing. Maybe you can take a brief look and decide which resources to pass to the customer. I think your illustration in the attached PDF seems helpful.