EVM430-FR6047: About length measurement of transducers in the same pipe

Hi Masaki,

This is the first time I have seen this.  Let me check with one of our USS experts.

Was the water temperature actually 22.40C for both measurements? A difference in temperature will affect Time of Flight/Speed of Sound, which in turn affects calculated distance.

Hi Masaki,

I recall you were having trouble with one of your EVMs.  Did you ever replace it?

Thanks for the reply.
The temperature is exactly the same.
We have a thermometer right next to the meter to check. We fill the pipe with water and then check that the temperature has stabilized before taking the measurement.
Is this a phenomenon that usually does not occur if the parameters are the same?
Please let me know if there is any place or method I should check.

Hello Dennis

Yes, I received a replacement and am using that one.

All the GUI is doing is measuring Absolute Time of Flight and multiplying it by the speed of sound of water at the temperature you specify. The 0.2cm would equate to ~1.3 uS difference between the two EVMs if 22.4C is indeed the fluid temperature.

Go into the waveforms tab and run both EVMs for a few seconds at least and compare the Absolute TOF values obtained with each EVM. If the GUI is reporting a difference in distance when you calibrate, there should be a change in Absolute TOF as well. It may also be helpful to compare an ADC Capture with each EVM to see where the waveform is in the window and find the peak amplitude.

Absolute TOF is calculated primarily through a correct setting of Configuration->Advanced Parameters->Envelope Crossing Threshold. If the threshold is not set correctly, there could be cycle slips which would mean there would be an error in multiples of the test frequency. For example, a cycle slip at 1 MHz would show a DToF ~1 uS.

Hello Dennis

Thank you for contacting us.
I understand that the difference in amplitude magnitude at high flow rates does not affect the flow measurement.

Am I correct in the way I described in question 1 regarding the "Envelope Crossing Threshold" setting value?

Hi Masaki,

I apologize for missing a response to your question #1.  Ans - Yes, based on the waveform you show, your method is correct.  A value of 10 (10%) is good.

Thank you for your response.
Do I need to set different values for each meter in the "configuration" such as threshold values? Or, if we are using the same design and the same model number of sensor, is it OK to fix them to the average value of each meter, etc.?

Hi Masaki,

One threshold value can be used for all, depending on how closely manufactured each transducers is.  Let me check if there is a preferred method to determine optimal setting.

We are currently using multiple sensors and Pipe to get ADCcapture. From those values, we are checking the variation of the peak and the first lobe. I am thinking of taking the process of determining the threshold value from the acquired variation data, is this a good idea?
Please let me know if there are any problems that can be anticipated.

I would like to check something else besides the issue of the threshold value. Should I ask a separate question in that case? Can I continue to reply here?

Thank you for your answer Dennis.

I have included additional questions in the additional PDF.
Please check it out

.About Signal Sampling Frequency.pdf

Hi Dennis.
I have two additional questions.
1, Do you have any documents that summarize trouble cases and design defects that may occur? (like DFMEA documents).
We would like to confirm in advance possible problems that may occur in the future as we proceed with the enclosure and board design.

2, Do you have any recommendations on how to evaluate and verify the reliability of ultrasonic water meters? In particular, we do not have much in-house expertise in testing the performance of ultrasonic sensors, so we would appreciate it if you could provide us with some guidance.
We would like to use it to measure tap water, and would like to evaluate it to prove that it can make stable measurements for 9 to 10 years.
Please confirm this in conjunction with the previous question.

Hi Masaki,

Let me check with our USS expert on both recent postings.

We look forward to hearing from you.

I have one more question.
Regarding the voltage, when I check the specifications below, it says that a voltage difference of ±0.3V or more between AVCC, DVCC, and PVCC may cause a malfunction.

If we have separate power supplies at PVCC, ADCC, and DVCC, and the voltage of one of the batteries drops over time, is there a possibility that the ultrasonic waveform will be affected and the position of the wave across the threshold will change?

If it will take time to confirm, please answer after the earlier question.

How is the progress on the question you are asking?
I have an internal meeting tomorrow evening, so if you have any questions that you can answer, even one, I would appreciate it if you could contact me first.
I apologize for the inconvenience.

Hi Masaki,

ASQ stands for acquisition sequencer.  Information can be found in the user's guide, page 463.

There isn't a lot of information about cycle slip, but can be explained by this illustration.  Basically, the absTOF uses the peak lobe closest to the threshold value.  In the illustration on the left, this is the first lobe.  If the threshold is set close the first lobe peak, then what can happen in high flow rates, the waveform can change slightly and the threshold can be closer to the second lobe peak as shown on the right.  The distance between the lobes is one cycle.  So if during a measurement the absTOF changes suddenly, this is usually due to a cycle slip.

Regarding the power supplies, if PVCC comes from a 2.7v LDO and AVCC, DVCC come from battery, then yes, AVCC, DVCC can only be as low as 2.4v.  But if battery drops to 2.4v, how is it possible LDO (low drop-out regulator) can produce 2.7v??  What is the source for input to the LDO?  The recommendation is to tie all three supplies together. 

To measure signals with the scope you can probe the CHx_OUT and CHx_IN pins.

Hello Dennis
Thanks for contacting me.

I understand about the ASQ. Thank you very much.

Regarding cycle slip, in your answer to #4, you said that if the value of Signal Sampling Frequenc is high, the possibility of cycle slip will be higher.

However, when I check the diagram you provided, I feel that this phenomenon occurs regardless of the value of Signal Sampling Frequenc.

What causes cycle slips when the value of Signal Sampling Frequenc is high?

Which pins are CHx_OUT and CHx_IN pins in the picture below?

Please let us know if you know the factors that make cycle slip more likely to occur when higher sampling rates are used. Based on past cases that your company is aware of, does this mean that a higher value of Signal Sampling Frequency is more likely to cause this?
Also, we are currently considering using a 1MHz transducer. Is 1MHz common for small to medium diameter (13mm to 40mm) water meters?
What are the reasons why 1MHz is chosen?

Also, what are the possible advantages and disadvantages of raising the frequency to 2MHz?

I understand about the location of the probe. Thank you very much.

Thank you for your answer. What parameters in USS need to be adjusted to set the correct excitation frequency?
Should I check FrequencySweep and adjust the Transmit frequency F1 value?
Or do I also need to adjust parameters that cannot be changed by USS alone?