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How about measuring capacitance or dielectric constant of the film? Using the film as the dielectric of a capacitor, the capacitance value would be inversely proportional to the thickness of the film. The measurement would be continuous, non-contact and unaffected by optical characteristics of the material. Sorry, can't think of a COTS solution vendor at the moment, but it shouldn't be too difficult to implement such a system.
thanks for your interest !
can capacitance measurement be calibrated at an accuracy of 1 micron.
( sorry for such question , iam a newbee hobbiest )
Yes, capacitance systems can read very accurately. SolveTech systems can be accurate down to 0.1 micron or better.
Your question has too little detail to really answer but if we assume your wanting to measure the thickness on the fly - i.e. whilst the film is moving Buy in a laser measuring instrument.
If the film is stationary then use a micrometer.
Various questions really need to be clarified:
To what accuracy?
Moving or stationary?
How many measurements per second/minute/hour?
Is the measurement non contact?
Is the film conductive?
How was this done before?
How will the data be stored,
What budget are you looking at
What sort of time scale
What skills do you have or have access to?
Thanks Rick !!!
i should have asked it properly,
thanks for guiding .
Yes BUT you didn't answer the questions.
I would also add where are you in the world?
Hi! Rick !!
Sorry for late reply.
iam a new bee / hobbiest in pakistan. have some basic skills in arduino . (skills mostly acquired from youtube). we planned to log / monitor our pvc / plastic film production line which is normally 22 - 30 microns (mostly transparent and non-conductive). along with logging our main aim was to keep our film at a constant thickness, i.e well between +- 1 micron. for which we need a non contact system. while searching on web, i found laser and ultrasonic systems. some suggest a capacitance method as well but i need to test its accuracy .
We started logging motors rpm, cycles, amps etc etc every second . now we are stopped at film thickness.
thanks for your interest
Good answer Rick
Now I don't know how they make thick plastic sheeting like 1/4 inch or more, but I worked at a company that made plastic extruders for thin plastic like shopping bags.
Considering he said during production and considering the extruders used for making plastic film or sheet plastic, I would say it is moving. After the plastic cools it is to difficult to control the thickness.
No contact, a contact gage will mark the plastic.
Constantly checked or a number of times a second depending on the feet a second.
The extruder head should be shaped like a donut, as the plastic comes out of the head they make a pressurised bubble. The bubble passes through a set of guides controlling the size and shape of the bubble. At the other end of the shaper they start the sheet on a motor powered role that pulls the plastic out of the head and you gage the thickness by the rate you pull the plastic. Ie faster is thinner and slower is thicker.
Laser gaging in most cases with a motor speed control to adjust the speed they pull the hot plastic through the bubble to cool in order to control the thickness of the sheet or film.
Considering this is during production and considering the extruders used for making plastic film or sheet plastic, I would say you want to gage the plastic as it is moving, after the plastic cools it is too difficult to control the thickness.
No contact, a contact gage will mark or damage the plastic.
If I have your question right, the extruder head should be shaped like a donut, as the plastic comes out of the head they make a pressurised bubble. The bubble passes through a set of guides controlling the size and shape of the bubble. At the other end of the shaper they start the sheet on a motor powered role that pulls the plastic out of the head and you gage the thickness by the rate you pull the plastic through the bubble and shaper. That is faster for thinner and slower for thicker film or sheet.
Laser gaging in most cases with a motor speed control to adjust the speed you pull the hot plastic through the bubble to cool in order to control the thickness of the sheet or film.
Hi Josehf !!!!!
you are there exactly there ..............
plastic film coming out of extruder head is not always constant, if at some point it is 25 microns than it may be 27 microns on other side of extruder ring.
we can monitor its thickness before we start rolling. ( bubble is cut into two flat sheets)
pl guide me what kind of laser equipment could help us.
can ultrasonic play any role over here ?
Laser Runout Gage for thickness.
I did not make them I just installed them on the extruder the rest was done by a specialist with proprietary knowledge.
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Posted:May 20, 2014
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