Hi everyone,

We want to build an ultrasonic thickness sensor circuitry that excites an ultrasonic transducer, read the reflected signal from a carbon steel stepped wedge and process it using a microcontroller.

Right now, we are exploring the excitation characteristics of an ultrasonic thickness sensor of type D790 SM (see link for specs). We tried to do so using a function generator of amplitude ~5V and frequencies up to 10MHz, and by varying the thickness of measured slab. Using a splitter, we connected the function generator directly to channel 1 of an oscilloscope and to the ultrasonic Tx/Rx was connected to channel 2. We wanted to see a delay varying with different slab thicknesses. However, we did not observe any delay. We got what appeared to be only an electrical delay due to different connections, if not just noise.


We made sure to use a specialized coupler fluid and the ultrasonic transducer is verified to work using an ultrasonic device (Panametrics 36DL PLUS).

Any suggestions?
Thanks!

 

It probably won't work.
Way too many variables for repeatability ...............

Satisfactory results could possibly be obtained
with a long-distance Laser-Reflection at a very low angle, and then averaged.

All of the following things, and more,
will affect the propagation of Sound through a material ...........

Material-Temperature,
Heat-Treatment variances,
Alloying variances,
Grain-Structure variances,,
Other Dimensions, aside from Thickness, affecting reflections and resonances,
Surface-Roughness,
Surface-Flatness,
Sample-Support-Structure, materials, design, and consistency of placement.


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It probably won't work.
Way too many variables for repeatability ...............

Satisfactory results could possibly be obtained
with a long-distance Laser-Reflection at a very low angle, and then averaged.

All of the following things, and more,
will affect the propagation of Sound through a material ...........

Material-Temperature,
Heat-Treatment variances,
Alloying variances,
Grain-Structure variances,,
Other Dimensions, aside from Thickness, affecting reflections and resonances,
Surface-Roughness,
Surface-Flatness,
Sample-Support-Structure, materials, design, and consistency of placement.


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.
.

Thank you for your input. I understand the complication of the sensory system, but why does it seem that we are not exciting the sensor at all? We want to see some delay that at least varies (for now not necessarily linearly and reliably) with different thickness. Note that we are using a stepped wedge.

Thanks again!

 

It would seem that You are expecting Ultrasonic-Sound-Waves to
travel through Metal like as if it's Air, or Water.
Solids act differently.

I can't speak from experience,
so maybe You can prove me wrong by finding an existing measuring device
that uses Ultra-Sonics for measuring metal-thickness,
which is both rock-solid-reliable and error-free.
Maybe one exists, but I doubt it.
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