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'[EE]: High Speed Thickness Measurement'
2006\09\25@134222 by John

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Hi Guys

I would like some suggestions for a thickness measurement project that I
have in mind. Its purpose when built will be to measure the thickness of
tissue coming out of a paper machine - ave speed 1500m/min

The standard means involve radioactive sensors or laser. Does anyone have
any suggestions for alternatives?

I am planning to base the design around an ARM processor. It needs to
provide a data stream, a digital output to show a warning alarm, a digital
output for paper break, aswell as a configurable 4-20mA output. The data
stream will be fed into a Honeywell DCS.

My main concern at this stage is choosing the measurement head - maybe even
designing one. I feel that it may need an array of sensors spread across the
sheet so that the even-ness of the sheet can be measured too. The
measurement heads could be mounted on an oscillating arm if need be.

Regards

John

2006\09\25@143950 by Steve Smith

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This a stupid (maybe) idea (long way out of my field)

Light permeability
For a lamp of given intensity the translucence of the sheet could be used as
a thickness measurement

Regards Steve

{Original Message removed}

2006\09\25@145945 by Vasile Surducan

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On 9/25/06, John <spam_OUTjohnTakeThisOuTspamraystorm.co.uk> wrote:
> Hi Guys
>
> I would like some suggestions for a thickness measurement project that I
> have in mind. Its purpose when built will be to measure the thickness of
> tissue coming out of a paper machine - ave speed 1500m/min

Microwave around 10Ghz, if the paper's temperature and moisture are constant.

Vasile

2006\09\25@150324 by John

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> This a stupid (maybe) idea (long way out of my field)
>
No Idea is stupid Steve, thanks for the suggestion

> Light permeability
> For a lamp of given intensity the translucence of the sheet could be used
as
> a thickness measurement
This could work if the light source is self calibrating, allowing for the
gradual degradation of the lamp.

Anyone know how well this could be used to measure a change of fractions of
a micron?

Regards

John

>
> Regards Steve
>
> {Original Message removed}

2006\09\25@151833 by John

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Something just occured to me -

Light is probably not the best because tissue production is very dusty, so
the light sensors will end up covered in dust, unless theyre continually
washed off.

Regards

John
----- Original Message -----
From: "Steve Smith" <.....xygaxKILLspamspam@spam@blueyonder.co.uk>
To: "'Microcontroller discussion list - Public.'" <piclistspamKILLspammit.edu>
Sent: Monday, September 25, 2006 6:38 PM
Subject: RE: [EE]: High Speed Thickness Measurement


> This a stupid (maybe) idea (long way out of my field)
>
> Light permeability
> For a lamp of given intensity the translucence of the sheet could be used
as
> a thickness measurement
>
> Regards Steve
>
> {Original Message removed}

2006\09\25@152220 by John

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Hi Vasile

The temp and moisure content vary.

Temp is dependant on the amount of steam being fed into the dryer drum, and
the speed of the machine - both operator set. The moisture content varies
depending on what the product requirement is - budget to luxuary and many
stages inbetween.

This doesnt mean that it cant be calibrated according to the conditions - it
will just make it a very complex measurement.

Regards

John
{Original Message removed}

2006\09\25@162303 by Bob Axtell

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I believe that thickness measurement is done with a radioactive source
and a "geiger" counter. The
thicker the material, the more attenuation. Easily calibrated.

--Bob

John wrote:
{Quote hidden}

> {Original Message removed}

2006\09\25@231209 by Vasile Surducan

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On 9/25/06, John <.....johnKILLspamspam.....raystorm.co.uk> wrote:
> Hi Vasile
>
> The temp and moisure content vary.
>
> Temp is dependant on the amount of steam being fed into the dryer drum, and
> the speed of the machine - both operator set. The moisture content varies
> depending on what the product requirement is - budget to luxuary and many
> stages inbetween.
>
> This doesnt mean that it cant be calibrated according to the conditions - it
> will just make it a very complex measurement.

20 years ago we've designed 10GHz moisture meters for some similar
"sheet" type DUT.
There are now on the market complex moisture meters in microwave range
measuring three parameters: moisture, temperature and thickness of the
material. Thickness is a constant inside the algorithm but could be
easily recalibrated for becoming the measuring parameters. I had an
advertising issue printed somewhere but probably will be hard to found
it now.

Vasile

2006\09\26@040142 by Alan B. Pearce

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>> This a stupid (maybe) idea (long way out of my field)
>>
>No Idea is stupid Steve, thanks for the suggestion

So here is my suggestion. Assuming the paper can be run over a rounded
surface (it could be an existing guide roller) so that you know it is flat
against the surface (i.e. under some tension), then my thought was to use
ultrasonic sensors to measure the thickness difference between the paper
height and the roller. You could have a number of sensors across the width
of the paper if necessary.

>> Light permeability
>> For a lamp of given intensity the translucence of the sheet
>> could be used as a thickness measurement
>> This could work if the light source is self calibrating,
>> allowing for the gradual degradation of the lamp.
>
>Anyone know how well this could be used to measure a change
>of fractions of a micron?

Yes. The way I would do it, taking the roller arrangement I suggested above,
is to shine the light so it is shining along the tangent of roller onto a
linear CCD. The roller will cause a shadow, which you use as reference, and
the paper will increase the shadow height. Readout speed will probably be
limited to the clockout rate of the CCD.

2006\09\26@044324 by Russell McMahon

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Id have thought that capacitive measurement could be quite accurate
for this.


       Russell


2006\09\26@045251 by John

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Thanks for the ideas guys.

I will investigate the use of ultrasonic, because the final stage had a
number of rollers on which this could work.

I am also interested in the 10GHz meter because it provides other
interesting measurements.

Will keep you all posted on progress as it forges on.

Regards

John
{Original Message removed}

2006\09\26@050429 by John

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Hi Russell

How would you do this? I can imagine using the sheet as the dielectric
between 2 plates. Would a tiny change in thickness create enough variance of
capacitance to measure accurately?

Regards

John
----- Original Message -----
From: "Russell McMahon" <EraseMEapptechspam_OUTspamTakeThisOuTparadise.net.nz>
To: "Microcontroller discussion list - Public." <piclistspamspam_OUTmit.edu>
Sent: Tuesday, September 26, 2006 8:38 AM
Subject: Re: [EE]: High Speed Thickness Measurement


> Id have thought that capacitive measurement could be quite accurate
> for this.
>
>
>         Russell
>
>
> --

2006\09\26@084558 by Rolf

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part 0 44 bytes
his is a multi-part message in MIME format.
part 1 3253 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

Since I have absolutely no idea about this sort of industrial control,
let me throw in my one idea...

... how about oblique laser light, and measuring the change in reflected
distance... let me explain...

Run the tissue over a a roller which is measured precisely. Put a sensor
which can detect the wavelength of the laser light immediately above the
paper with perhaps a light tube.

Shine the laser at a very oblique angle on to the tissue, and measure
the angle you need to shine the laser on in order to get the beam under
the light tube... like this... actually, perhaps a better method will be
to shine the laser at a known but very oblique angle, and to then use a
"heliostat" mechanism to track where the dot is reflected... like the
attached image. The thickness of the tissue will be proportional to the
angle you have to adjust the sensor to to get the sensor pointed at the
laser dot.

Rolf

John wrote:
{Quote hidden}

> {Original Message removed}

2006\09\26@093645 by John

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Hi Rolf

I kinda like this one. It allows the light source and sensor to be located
away from the machine workings. It also makes for easy experimentation on a
live systemwithout affecting production. Thanks

Regards

John
{Original Message removed}

2006\09\26@120338 by Russell McMahon

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> How would you do this? I can imagine using the sheet as the
> dielectric
> between 2 plates. Would a tiny change in thickness create enough
> variance of
> capacitance to measure accurately?

If you can maintain a sensor at a small distance above the paper as it
eg travels over a roller then the change in capacitance should be
highly proportional to paper thickness. Dielectric constant of paper
relative to air (1) governs how large a swing you'll get.



       Russell


2006\09\26@124033 by Dominic Stratten

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Dont forget the vast amounts of static these machines generate.

I used to run a paper converting machine many many years ago and the sparks
from the static generated by the paper unrolling, cutting and re-rolling was
enough to jump 3 or 4 inches.

I still have nightmares to this day about walking up to the machine and
getting zapped by a couple of hundred thousand volts lol.

Dom
{Original Message removed}

2006\09\26@125643 by John

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Hi Dom

I am not sure how they combat static on our machine, all I know is that I
havent been shocked yet. It may be because most of the process is wet, with
only the very last stage being drying, creping and rolling onto the reel.

Cheers

John.
{Original Message removed}

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