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Since air is so absorptive with respect to ultrasound higher excitation voltages are required. How high, depends on several factors:
In a nutshell 1-3 above all relate the SNR of my ultrasound signal path. Changing any of the above will the size of my echo and reduce my measurable distance.
For ease I used the TDC1000_GASEVM as it:
I mounted it on a blank PCB board which I then attached to a hammer drill with velcro straps.
Testing in the lab yielded some promising results:
With Drill running and no depth change (no hammer mode)
In air a STD of 3.02us yields [343 m/s*3.02e-6)/2] approximately .5mm
With drill running in Hammer mode(and no depth change)
So drilling with no depth change and no filtering other than averaging yields:
In air a STD of 18.774us yields [343 m/s*18.774e-6)/2] approximately 3.2mm
What EVM/drill combo looked like:
During testing (note: metal plate used to make zero depth change)
If the drill is not orthogonal to the surface by more than 10 degrees (approx.) no echo is detected (due to the tight beam transducer used).
The vendor link: (http://www.bestartech.com/sensors-waterproof-sensors-c-1_21_23-l-en.html)
Arrow’s link: (https://www.arrow.com/en/products/bpu19200ifah11/bestar-technologies)
Another thing to keep in mind is this setup setup can be used to do level sensing in a container "From the Top" of the container. The issue with that application is that any liquid condensing on the transducer face will severely limit range and will require experimentation.
Also it is ESSENTIAL to read my app note on Sensing Level as it goes over understanding and characterizing transducer ring-down for your system and how to adjust the TDC1000 to compensate for it.
In reply to Oleg Kobrin:
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In reply to Russell Engebretson:
Could you please also help me?
I have oscilloscope attached, and now I see the trails of echo signal, but it is very weak!
In reply to Nancy Stone:
I worked with this board and helium for quite a while and I managed to get it to mostly work for my application. A couple tips I can give you is that the transducer will not couple with helium as well as it does with air, so your signals are going to be a lot smaller, which is why you notice they do not work at a distance as well.
Also, helium is the lightest material and therefore the speed of sound in helium is a lot larger than any other gas you would use. For this reason, with the timing of the board, there are limits on how close you can have your transmitter/receiver before you lose your signal in the ringdown of the transducer; I believe in my case I kept my transducers around 10 cm apart. All I can say is you are going to need to play around with the timing registers, the threshold voltage, number of stop pulses and such.
I also had this board communicating with a raspberry pi, so a lot of the jumping of the signals due to fluctuating signal strength I removed through software and manipulation of the data. Do you need to use helium? and what is your application in helium? I made a device to determine the purity of helium flowing through a pipe. It worked really well actually, but there are more issues which arise if you are changing the concentration of helium.
Yes, I did the same thing as you are trying to do. I managed to get my setup to work well, but there were some issues which needed to be overcome and I didn't end up finishing a final product (not that it couldn't be done). Some issues which you are going to notice as you play around with this is that the amplitude of your signal will also change as you drop in helium purity, and not linearly. So your signal amplitude increases and decreases several times throughout the whole process from 100%->0% helium purity - In fact, at some mixtures with air, the signal nearly disappears. We never officially discerned what was the cause of this, but I theorized that it could be due to the harmonic modes inside the pipe which would change as purity changed, causing increases and decreases in the signals. There could also be other explanations, but I didn't worry too much about this, I just worked around the issue.
You are going to need to play with the distance between transducers, threshold voltage, timing registers, and number of stop signals, until you can get your board to accurately detect the signal in the full range of 100%-0%. Another issue which arises is that your stop signal jumps between periods in your received signal, due to the large fluctuations in amplitude of the signal. I simply offset this through software, which worked very well in tests I did, but it put limitations on my device.
This is a very interesting project, and I will most likely finish it eventually, I just don't have the time currently. If you have any questions or problems feel free to privately message me on here and we can discuss further.
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