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Author Topic: Density sensor of solids  (Read 2526 times)
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Hi!

Anyone knows some density sensor to use in solids?
     
Abs.
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If the 'density' you want to measure is the ratio of mass to volume I know no way of measuring it directly.  Typically you measure the volume and mass separately and do the division.

Can you explain what it is you want to measure the density of?
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Define density, define solids...  Very little information to go on here.
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I'll try to define what exctly I need  smiley-draw.

I need to know if a piece of wood have structural conditions or not.

A good way to know that is look to the density of piece. When the wood loses mechanical properties the mass is reduced, resulting in lower density wood. The lower density echoes in a different way, so with an ultrasound (knowing the answer of a wood healthy) we can tell if the wood retains its mechanical properties.

An additional problem is that pieces don't has the same general shape (the length varies considerably as well as the geometric shape) making impossible a mathematical approximation (I think).

Thus I believe that the only way to know if the wood maintains his density either by direct analysis.

Forgive me for not having more information inserted in the first message ... Stupid beginner!   smiley-red smiley-red smiley-red

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Well we know the type of material is fixed, so that going to make things easier.  Probably the cheapest approach is
some sort of acoustical techique as you imply, but some sort of high tech neutron or X-ray transmission/backscattering
might work too (big budget!!).  Acoustical measurement is going to depend on shape though...

Trying to measure dielectric constant might work for some types of material, but for wood the moisture content would
probably dominate the reading making it meaningless.

Thermal conductivity might be a possible property that correlates to density - or heat capacity.
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So basically there is no simple sensor that will give you what you need to know.

You will have to use indirect measurements. This is more like a research project that a build it project.
I would suggest that acoustic step impulse ( a knock ) and analysis of the reverberation might give a clue to this.
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Measuring the moisture content of the wood might provide a good indirect measure of structural strength.  Moisture measuring devices are widely available.
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Moisture measuring devices are widely available.
You can do that by measuring the absorption of microwaves.
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I need to know if a piece of wood have structural conditions or not.

You might consider measuring the hardness of the wood with a durometer tester.
www.fvfowler.com/resource/pdf/2304/2304_374-375.pdf

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Quote
I need to know if a piece of wood have structural conditions or not.

You might consider measuring the hardness of the wood with a durometer tester.
www.fvfowler.com/resource/pdf/2304/2304_374-375.pdf



JavaMan, is impossible to use a durometer tester in this application, 'cause I'll do these tests in movement...

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Moisture measuring devices are widely available.
You can do that by measuring the absorption of microwaves.

Grumpy_Mike, do you know any component that makes this microwave emission and subsequent reading? That can be a way to do that...

Measuring the moisture content of the wood might provide a good indirect measure of structural strength.  Moisture measuring devices are widely available.

On the other hand, measure moisture in a opened local, that may be subject to rain, in constant motion without touching the wood is impossible (googled a bit and found nothing of the sort)...
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When the wood loses mechanical properties the mass is reduced, resulting in lower density wood.

This seems to be a dubious claim.   What sort of circumstances do you expect this to occur in ?
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When the wood loses mechanical properties the mass is reduced, resulting in lower density wood.

This seems to be a dubious claim.   What sort of circumstances do you expect this to occur in ?

Michinyon, I disagree that this is a dubious claim.

Is known that the mechanical properties of a wood (whether efforts normal, tangential, tearing or bending) are given by the entanglement of fibers. Thus the density of tangled fibers is directly related to its resistance.
When the wood begins to suffer composition (whether it be biological or chemical) that wood density is reduced and loses the properties. We see it every day when we look at a rotting wood, she loses weight (on density), resistance efforts (on density) and its initial format for the decomposition of the fibers.
Following this line of thought, different densities reverberate ultrasound (or microwave, as suggested by a colleague) in different ways.
What I intend, with the help of colleagues at the forum, is to find a way to measure the deterministic reverberation to know the states limit the wood.
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OT: I once spent a day with a phone company linesman.
Before climbing a pole, he was supposed to strike the base of the pole with a hammer.
A safe pole is supposed to "ring", but an unsafe one (wet or dry) just gives a dull "thud".

He had been carefully trained to listen and feel for the differences, and had to use a particular hammer, with a particular swing at a particular point on the pole.

Instead, he would simply drive his truck slowly into the pole, figuring that if the pole survived that, it was safe to climb.
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Destructive testing of a sample might return the information you want...

Bob
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tbaroni,

Is it a hardwood or a softwood?

What type of wood species?
(Some species of wood have a more homogenous structure than others)

Is the test specimen quarter-sawn, rift cut or plain cut?
(This effects the orientation of the growth rings which are a different density than both the heartwood and the sap wood . . . what about knots, they have a very high density even compared to heartwood)

Will all test specimens be the same size and moisture content?
(If not, then acoustical properties will not be an effective physical characteristic to determine mechanical properties)

One of the problems of using wood as an engineering material is that it is a natural product, grown in an uncontrolled environment and wood from different trees of the same species may have widely different mechanical properties.

Although cost is an issue; the variability of physical properties in natural wood for structural construction, is also a major driving force in the proliferation of engineered beams and engineered structure wood elements (including plywood, particle board and chip board) all of which have more consistent mechanical properties than anything actually grown in a forest.
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