# Arduino Forum

## Using Arduino => Sensors => Topic started by: tbaroni on Nov 20, 2012, 07:51 pm

Title: Density sensor of solids
Post by: tbaroni on Nov 20, 2012, 07:51 pm
Hi!

Anyone knows some density sensor to use in solids?

Abs.
Title: Re: Density sensor of solids
Post by: johnwasser on Nov 20, 2012, 11:15 pm
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?
Title: Re: Density sensor of solids
Post by: MarkT on Nov 20, 2012, 11:52 pm
Define density, define solids...  Very little information to go on here.
Title: Re: Density sensor of solids
Post by: tbaroni on Nov 24, 2012, 10:44 pm
I'll try to define what exctly I need  :%.

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:

Title: Re: Density sensor of solids
Post by: MarkT on Nov 25, 2012, 01:23 am
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.
Title: Re: Density sensor of solids
Post by: Grumpy_Mike on Nov 25, 2012, 01:28 am
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.
Title: Re: Density sensor of solids
Post by: johnwasser on Nov 25, 2012, 04:45 pm
Measuring the moisture content of the wood might provide a good indirect measure of structural strength.  Moisture measuring devices are widely available.
Title: Re: Density sensor of solids
Post by: Grumpy_Mike on Nov 25, 2012, 09:21 pm
Quote
Moisture measuring devices are widely available.

You can do that by measuring the absorption of microwaves.
Title: Re: Density sensor of solids
Post by: JavaMan on Nov 26, 2012, 05:06 am
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

Title: Re: Density sensor of solids
Post by: tbaroni on Feb 10, 2013, 05:12 pm

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...

Quote
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)...
Title: Re: Density sensor of solids
Post by: michinyon on Feb 11, 2013, 01:42 pm
Quote
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 ?
Title: Re: Density sensor of solids
Post by: tbaroni on Feb 12, 2013, 01:18 pm

Quote
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.
Title: Re: Density sensor of solids
Post by: AWOL on Feb 12, 2013, 02:20 pm
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.
Title: Re: Density sensor of solids
Post by: Docedison on Feb 12, 2013, 03:05 pm
Destructive testing of a sample might return the information you want...

Bob
Title: Re: Density sensor of solids
Post by: I_lurk_no_more on Feb 12, 2013, 07:37 pm
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.
Title: Re: Density sensor of solids
Post by: michinyon on Feb 13, 2013, 01:54 pm
It remains a dubious claim,  in my opinion.

There are many different ways in which wood "loses mechanical properties".   Abrasion,  rot,  fatigue, splitting, variations in moisture.
To assume this is related to "loss of mass",  or indeed "density",  seems naive.  Wood also shrinks and swells under various conditions,
which, by definition, affects the density.

You refer to wood rotting.  This usually involves the wood becoming wet.  Wood which has become wet,  and is rotting,  will
appear to have a higher density than it had when it was dry.

Then there are hundreds of species of wood to consider.
Title: Re: Density sensor of solids
Post by: michinyon on Feb 13, 2013, 01:58 pm
You refer to ultrasound testing of wood.   That's a good approach.   Sound wood will tend
to transmit sound,  unsound wood will tend to absorb it.   You can measure the rate of attenuation
of the ultrasound and draw conclusions from that.

Be that as it may,  there are many ways wood can become unsound,  without "losing mass", as you claim.
Title: Re: Density sensor of solids
Post by: Arnoldo on Apr 24, 2019, 03:55 am
In thinking about this and some of my knowledge about materials, it seems to me a great deal of information about the density of material could be derived from sound waves. The frequency of sound traveling through dense material is different than when moving through lighter weight material. For example, we already know sound waves move faster through dense material. Also, working with various acoustic material, we know that spongy material absorbs sound. Higher density sponge rubber, for example, has a sound deadening effect while hard material can have a completely different sound response. Playing around with different frequencies and volume of vibrations through different materials, you could establish a record of the condition - density - of the material.

Suppose you might attach a piezo element to a piece of wood and cause it to vibrate at say, 20 kHz. By recording the vibration frequency and volume at some set distance from the emitter, through the material with a microphone or vibration sensor, you could conceivably establish a record of how the material might change over time. In speculating about it, fresh, 10% moist oak might have a readable difference if it were dried to 5%, or soaked to 15%. One could conceivably test a sample of dry-rotted wood or termite infested wood with the same device and eventually establish some sort of background record that would let you alert to the actual condition of the material in question. I know for a fact that wet wood transmits vibrations in an entirely different way than dry, so this method could establish "test points" in a structure to determine if the wood is suffering intermittent or continuous wetting in place that might be hidden from easy inspection, thus pinpointing serious conditions before they become a more extensive problem.

Just a thought.