yes...like extrusion only pulled rather than pushed
makes (in our case) structural elements of FRP
I need to measure the wall thickness of a RHS without contact...on all sides
Or at least without gel between the transducer and material
And while I am here;
Pull speed is measured by 2 encoders, 1 on each puller (they look like
Dynapar cubes of some sort), through a Red Lion ADC to a Koyo PLC.
Its all over the place and longer averaging time does not help...might
it be affected by noise?
As far as I can see the signal lines run with 110V control lines
So you have an analog signal (the wheel position) which you convert to
digital (via the encoder) then you convert it to analog (via the Red
Lion DAC) then it goes into a PLC where it is converted to digital so
the PLC can use it?
God I hate excess conversions.
Are you sure the reason that the reading is all over the place isn't
that the actual speed is all over the place? The fact that longer
averaging doesn't help indicates that the noise (or actual speed
variation) is of lower frequency than the cutoff of the filter -- I
can't say what that means in your context but perhaps it suggests something.
The measurement system seems to be ad-hoc idea piled on ad-hoc idea,
turtles all the way down. To answer the question put, if the shape comes
through a die with a core, the core can be extended and used as one
plate of a capacitor. Provided the material's dielectric constant is
really constant, a good measurement can be had that way.
Thickness can vary not only because of changing pull speed, but because
of temperature variation in the feed stock. Drawing is much more
sensitive to that than extrusion. (Extrusion forces the material against
the die, but drawing pull the material away.)
Engineering is the art of making what you want from things you can get.
Yes, it may have been done to make programming a bit easier
And the PLC is full, the designer left no room for expanding / modifying
Yes...it may vary a small amount but not as much as indicated (+-
anywhere up to 100mm/min every update) The speed control valving is of
good quality and independant to PLC...originally it was controlled by
the PLC and the pull was jerky and unusable so was replaced with an
independant unit...probably jerky due to unstable speed information!
Hmmm, goes to investigate noise and filters
Ultrasonics is a good way to go, but expensive to set up the appropriate
hardware. For truly non-contact measurements, I'm thinking Laser
Generated Ultrasound would be your best bet (I should admit that this is
my field of study so i might be a little biased). You could use a Nd:YAG
or similar laser to generate the ultrasound and an interferometer to
pick it up. Unfortunately, if the thickness is small (roughly less than
a quarter of an inch) the types of waves generated will be very complex
(they are called Lamb waves). This makes the signal processing very
Is this meant to be an on-line application or post manufacturing
measurement? Doing the meaurement in a manufacturing environment leads
to noise issues.
I suggest you do some research on Google or similar to find past methods
for measuring wall thickness in fiberglass laminates.
Also, check out http://www.ndt-ed.org/index_flash.htm for background
info on nondestructive measurement techniques.
Hope this helps,
A Beta gauge
The preceding message represents personal opinions
and/or advice that may prove incorrect or harmful. But then maybe not.
Feel free to disregard.
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There are certainly ultrasonic thickness testers around, but for an
'outside-the-box' idea, have a look at Ultrasonic Level Transmitters.
If you pick a high-frequency short-range one and install it above the web
looking down, some (eg. IIRC www.hawklevel.com) can output the difference
between two boundaries in air and may, with a bit of tweaking, be able to
read continous thickness of the sheet.
Make sure you get the rep to demonstrate whether or not he can do it before
If you have access to both sides of the material you could consider a
surface distance measurement (either laser or ultrasonic) from each
side and calculating the difference. This could be potentially less
problematic than attempting to measure "through" the material though
you now have two sensors to maintain and accuracy could be an issue if
you are dealing with a very thin material.
This can be made with ultrasound, but - as far as I know - nobody offers
ready made solution.
Normal ultrasonic measurements (they are standard for example for pipes
made with extrusion method) are using water as contact medium.
Measurement in the air (contactless) can be made too, but requires a
relatively expensive development.
Because we have developed some ideas for this kind of measurement (based
on our experience with water based measurements), I have even tried to
convince some companies to finance such development, but without succes.
It is also possible to make such measurement using x-rays, based on
tomografic principle, but this can be even more complicated.
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