"Short Wave Sportfishing" wrote in message
...


2 - How can you make a content analysis of any material without first
starting at a reference point? If that reference point isn't zero,
then was is it?

3 - If the baseline is not zero, how do you determine what zero is?

I am very interested in your response - I wish to be enlightened.

Later,

Tom

Howdy Tom,

I was following this thread with casual interest until I realized that
moisture meter is, as the other poster suggested, really a density meter. I
am curious if it is really a ultrasonic density measuring system. I recall
that they are calibrated using calibration blocks of a material with a know
and certified density.

Eisboch

On Sun, 20 Mar 2005 19:01:50 -0500, "Eisboch"
wrote:


"Short Wave Sportfishing" wrote in message
.. .


2 - How can you make a content analysis of any material without first
starting at a reference point? If that reference point isn't zero,
then was is it?

3 - If the baseline is not zero, how do you determine what zero is?

I am very interested in your response - I wish to be enlightened.

Later,

Tom

Howdy Tom,

I was following this thread with casual interest until I realized that
moisture meter is, as the other poster suggested, really a density meter. I
am curious if it is really a ultrasonic density measuring system. I recall
that they are calibrated using calibration blocks of a material with a know
and certified density.

Howdy Sir - how's the weather?

It depends on your definition of density. Using a standard definition
of density like the mass per unit volume of a substance under
specified conditions of pressure and temperature, then no, a moisture
can't measure density in that sense.

You measure density by specific gravity - that is weighing the
material in question or determining it's relative hardness (density)
by deforming the surface or the shape of the material in some manner
and measuring the force needed to do so. Then applying some
mathematics, you have density.

As I understand it, and have demonstrated to myself by playing with
the one I have, moisture meters measure resistance. They do this by
using a 1 KHz modulated signal anywhere from 5 to 40 KHz in frequency
across a predetermined distance (centers of the probes or pads).

The presence of water would necessarily mean that there was lower
resistance, but it doesn't mean that the material is less dense.
We're not dealing with a solid block of something - this is woven and
porous fiber. The density of the fiberglass and resins isn't the
issue - it's the water in, through and surrounding the fibers and it's
penetration through the resins.

Think of it this way. If you fill a ceramic bowl with water and put
the meter pads in it, what are you measuring? The amount of water in
the bowl or the density of the bowl?

Yes/No?

Later,

Tom

"Short Wave Sportfishing" wrote in message
...

It depends on your definition of density. Using a standard definition
of density like the mass per unit volume of a substance under
specified conditions of pressure and temperature, then no, a moisture
can't measure density in that sense.

You measure density by specific gravity - that is weighing the
material in question or determining it's relative hardness (density)
by deforming the surface or the shape of the material in some manner
and measuring the force needed to do so. Then applying some
mathematics, you have density.

As I understand it, and have demonstrated to myself by playing with
the one I have, moisture meters measure resistance. They do this by
using a 1 KHz modulated signal anywhere from 5 to 40 KHz in frequency
across a predetermined distance (centers of the probes or pads).

The presence of water would necessarily mean that there was lower
resistance, but it doesn't mean that the material is less dense.
We're not dealing with a solid block of something - this is woven and
porous fiber. The density of the fiberglass and resins isn't the
issue - it's the water in, through and surrounding the fibers and it's
penetration through the resins.

Think of it this way. If you fill a ceramic bowl with water and put
the meter pads in it, what are you measuring? The amount of water in
the bowl or the density of the bowl?

Yes/No?

Later,

Tom

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may (or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law and
others) although we delt with the refractive index of a material rather than
it's density. I donno ... just a thought.

Eisboch

On Mon, 21 Mar 2005 04:38:53 -0500, "Eisboch"
wrote:

~~ snippage ~~

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may (or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law and
others) although we delt with the refractive index of a material rather than
it's density. I donno ... just a thought.

Just so that I'm not missing something (which is possible - I'm not
the brightest bulb in the drawer), allow me to explain my thought
process here.

For one thing, water is relatively transparent to ultrasound under
normal conditions. It will reflect hard returns like thermoclines for
example and that is a density change I admit, but the distance from
the surface or transducer, the water is transparent. So in one sense,
yes, it does measure density.

However, when you are dealing with the presence of internal water in a
dense material, how to you measure it? To strain the bowl analogy a
little, what are you measuring for - the presence of a bowl or the
presence of water? If you reflect ultrasound into the bowl and get a
hard return, does that indicate that the entire bowl is solid or that
there is a hard bottom indicating the presence of a bowl?

To my simple mind, to test for the presence of water in any material
you start by measuring resistance to electrical signals (and the
argument can be made about density there also, but there is a subtle
difference). The more water, the less resistance and vice versa.

If you take a uncompromised piece of fiberglass as a base line, flip a
signal through it and use that as zero or base line, any changes have
to be due to decreased resistance to the signal.

Right?

Later,

Tom

"Short Wave Sportfishing" wrote in message
...
On Mon, 21 Mar 2005 04:38:53 -0500, "Eisboch"
wrote:

~~ snippage ~~

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may
(or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law
and
others) although we delt with the refractive index of a material rather
than
it's density. I donno ... just a thought.

Just so that I'm not missing something (which is possible - I'm not
the brightest bulb in the drawer), allow me to explain my thought
process here.

For one thing, water is relatively transparent to ultrasound under
normal conditions. It will reflect hard returns like thermoclines for
example and that is a density change I admit, but the distance from
the surface or transducer, the water is transparent. So in one sense,
yes, it does measure density.

However, when you are dealing with the presence of internal water in a
dense material, how to you measure it? To strain the bowl analogy a
little, what are you measuring for - the presence of a bowl or the
presence of water? If you reflect ultrasound into the bowl and get a
hard return, does that indicate that the entire bowl is solid or that
there is a hard bottom indicating the presence of a bowl?

To my simple mind, to test for the presence of water in any material
you start by measuring resistance to electrical signals (and the
argument can be made about density there also, but there is a subtle
difference). The more water, the less resistance and vice versa.

If you take a uncompromised piece of fiberglass as a base line, flip a
signal through it and use that as zero or base line, any changes have
to be due to decreased resistance to the signal.

Right?

Later,

Tom



No, actually I consider myself a middle of the road .... oh .... sorry ... I
forgot we were actually talking boats here.
Seriously - I don't know. I just never stopped to think about how a
non-invasive "moisture" meter worked.

Eisboch