What type of sensor for this task

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We are using a coating machine that has two rollers. A small amount of UV ink rides between the rollers.
I am using a peristaltic pump to add ink as the machine runs.

What would be a good sensor to use that I can control the pump that feeds the ink.

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I gather you want to control the amount of ink so that it doesn't overflow the rollers.

You could have a simple light beam set to the required level. When the liquid obscures the light beam, you stop pumping.

There are laser rangfinders that came measure millimeter levels, so they might be suitable but they are expensive.

Have a look at companies like Sick ( www.sick.com ) and Banner ( http://www.bannerengineering.com... ).

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Maybe illuminate the roller with a UV source then look at the resulting fluorescence with a standard photo-diode.

Greg

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Depending on task specifics maybe Sharp Distance Sensor 2Y0A21 or alike would fit.

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Its a hard problem for several reasons. First, it has to be moving, so the liquid surface is not steady. And, the surface has to be curved.

What is practical will depend, a lot, on how full that space is filled with the liquid. That is, at the liquid surface, how wide (distance, roller to roller)?

How is it being controlled now?

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Is contact with the liquid permitted? If so, a float valve of some sort might be the easiest solution.

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Is the UV liquid conductive, and the rollers non-conductive?

If so, then add a metalic band to each end of the rollers and measure the resistance of the "column" of liquid.

The length of the "resistor" is fixed, but it's cross-sectional area increase with the amount of ink present.

JC

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Thank's for the input.
To answer some questions.

Rollers are 20" in length
The Ink is actually cured by UV but a small UV led would not make any effect on curing.

The space can be filled to the tops of the rollers, there is a plastic end piece on each end to stop the flow from falling off the ends of the rollers.

So the total depth of the liquid may be 0.470 inches.

My initial thought was as Chris suggested, to use a float. It would be the lowest cost approach.

This is the machine it's the EZ Koat 20
http://www.kompactech.com/coatin...

I tested the machine at the HP demo site in Atlanta last week, they are partners with Kompac. That machine did have what looked like an Omron cylindrical sensor, perhaps a capacitive sensor.

The manufacturer wants $1500.00 for the sensos. because i am cheap i figured I would have a go at saving a few bucks.

So i think Float is the way i am going to go, the Sharp sensor has little lenses that would perhaps load up with splashed material.

I have been pondering a design like this. Adjustable balance to make it sensitive with a small narrow float.
The actual sensor could be a simple IR detector/emitter.

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Maybe illuminate the roller with a UV source then look at the resulting fluorescence with a standard photo-diode.

I like that Idea as well, more fun to design and test. The liquid will be clear but while running would be white (full of air bubbles) so it might work well.

I will post a picture of the device I make when we get the machine.

Thank's again folks for the input.

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You could also use a pressure sensor with a piece of tubing descending into the liquid. The higher the ink level, the higher the pressure in the tube will be.

Some (larger scale) examples:
http://ugt-online.de/uploads/pic...
http://www.freepatentsonline.com...

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How about to make a hole on the side plastics and let the excessive liquid to drain back to the tank. This way you don't need to control the pump. If you insist to control the pump, you can add a simple DIY flow sensor in the drains.