Monitoring product density


Thread Starter

David Berry

Hi list members,
I have an application where the characteristics of a product formed by an extrusion process are required to be automatically controlled. The
most desirable way to determine the product characteristics appears to be by measuring the amount of light transmitted through the product.
The product material (about 1cm thick) itself is more or less opaque, however there are voids where light will shine right through, similar to
a woven material.

I am investigating the use of a stabilised light source and photodetector operating in similar way to a standard turbidity meter. A camera may be preferable to a small photodetector as the
measurement may need to be over an area of say 50mm diameter to allow for some averaging. The system will need to provide an output signal such as 0 - 10V or 4-20mA to be used for controlling the extrusion process speed.

If anyone has any ideas about how to set up such a system or know of suppliers of suitable equipment and would care to post them to the list
or to myself, it would be much appreciated.

David Berry

Cozmac Automation Ltd
[email protected]
It isn't clear from the text of the message that what you want to measure is density.

If you do, you might consider using a very small gamma source and a scintillation detector. Because of the thinness of the product material,
and the speed of the line, you might have to have somebody make you a laboratory-size version. You might have to use Americium rather than Cesium
as your source.

All of the industrial nucleonics companies have successful applications with polyfoam density on extruders, polyol density in injectors, and other
"non-traditional" measurements. Try TN/Kay-Ray/Sensall or Ohmart/Vega for advice.

Walt Boyes

------------------Walt Boyes----------------
SeaMetrics Inc. Flow Meters and Controls
P. O. Box 1589 Kent, WA 98035 USA
253-872-0284 voice 253-872-0285 fax
mailto:[email protected]
Hi David,

We did a similar project a few years back where we had to measure the opacity of injection molded plastic cases. It was to ensure UV protection for the end product placed within the case. I had very good luck using Keyence's PS-T1 and PS-V1 photoelectric amplifiers. They had a easy to change setpoint to give a digital pass/fail output. I also found it neat that the display changed from red to green to show if the actual value was above or below the setpoint. I don't remember if it had an external analog
output, but you may not need it with this sensor. In any case, Keyence is familiar with measuring opacity, so maybe they can help
with your application.

Good luck,

- Eric Nelson
[email protected]
Packaging Associates Automation Inc. [email protected]
Rockaway, NJ, USA

ravi chandran

Dear sir,

At my site we use x-ray to measure the thickness of the material extruded and of cause the diameter. The device will show you four angle of
measurement and can be link to your extruder to control the screw rpm in order to have a stable thickness. The machine supplier is Sikora
Industrieelektronik Gmbh. Germany.

ravi,fp technologies

Johan Bengtsson

Would a simple system like this give enough accuracy:

put the material to invesigate between two "milk colored glasses" (don't know the native english word), put the light source on one side and the detector on the other. Both the detector and the
light source should be placed at some distance.
This will make the averaging quite good.
Putting this in a dark environment would be preferable but the effects of surrounding light could be minimized by using LED:s as the light source and modulate them.

converting the signal to 0-10V or 4-20mA is left as an exercise to the reader... :)

If this is not accurate enough and this is because differences in the voids a standard vision system may be useable. It would be no
problem to program it to remove all of the ares brighter than some limit before averaging the rest.

/Johan Bengtsson

P&L, the Academy of Automation
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]

Giovanni Rossi

sorry,this reply is very late.

I hope that You found a solution among the good reply within this page.

But may I help you?

Schneider Electric has in its "Telemecanique" catalogue a throughbeam photosensor with analog output (4 - 20 mA). The emitter is an infrared led, and, at a distance of 100mm the receiver get 250.000 times the light that it need to work.(The gain is 250.000).
The reference is XU2M18AP20D.

Best regards
Giovanni Rossi
Schneider Electric Branch office in Bologna.