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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.
Here's a few more pics showing TDC1000 GUI tabs and scope shots at the minimum and max range:
Setup tab: Note CPU_CLK source set to 1.6Mhz
TDC7200 tab with the "mask bits" set to ignore the ringdown Stop pulse (see scope shots below)
Scope shots showing: Start (Ch1/Yellow), Stop (Ch2/Green), Compin (Ch3/Purple)
Transducer ringdown based Stop pulse circled in red:
Range at 16cm:
Range at 70cm:
Tank tab with air Speed of Sound showing 16cm
Tank tab with air Speed of Sound showing 70cm
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In reply to Matthew Minasi:
I am currently trying to detect the concentration of a very light gas with a very high speed of sound and am looking to be able adapt flow rate. For this I believe I need to reduce the distance between my transducers to increase signal size for accuracy. I am just wondering if you have any advice for reducing the transducer ringdown signal in the receiving path so that I can bring the transducers closer together?
thanks in advance,
In reply to Russell Engebretson:
I tried the pictured GUI setup with the same frequency (200kHz) transducer, and my oscilloscope is showing no signal and my graph has no data. Any ideas as to what could be going wrong?
More importantly, what would I have to change about your method/settings above to be able to apply this technique at distances of a few centimeters?
In reply to Nancy Stone:
I went through this process a while back and there are a bunch of settings you have to play with. If you are using the register values listed here, there is a minimum distance from emitter to receiver of 17cm (as listed at the top). This is because there is a blank period which the receiver is "not listening". If you spread your emitter/receiver further from each other you should pick up a signal. If this is the case, then you need to play with the registers in the Timeout section of the TDC1000 tab - enabling the force_short_tof register should allow you to pick up signals closer to each other.
It has been a while since I played with the EVM, but if you have questions I should be able to help you out.
Also, are you doing this in air? or another gas, I was dealing with helium which introduced many other obstacles.
Sorry for the extremely delayed response, I do not know if you still need assistance with this project?
If you are still stuck there are a few things to try. First, do you have an oscilloscope to hook up to the board? Can you see your received waveform?
One issue which may be causing the constant trigger, independent of transducer distance, could be that the trigger is being set due to the ring down of your transducer? you could try increasing the threshold value from -35mV to something higher and see if that helps.
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