Foam detection, what works for you?

I have an application where a sticky foamy product is vacuum cooled in a large vertical vessel. I'm currently using two Capacitance probes for high and low with a deadband control scheme. When the high probe is made I kill the vacuum until the low probe breaks.

The problem is that the capacitance probes foul in about 2-3 days, and give false readings. So I'm looking for a different technology. The foam is of variable density. I've tried ultra sound, radar and guided radar, from almost all of the major vendors. I currently trying something similar to the Capacitance that's based on RF Admittance.

I know some of the forum members have experience in waste treatment plants, and may have a better method of foam detection. I'm willing to try almost anything that has some hope of working, and is fouling resistant, non-contact would be ideal.

I suspect that powerful enough infrared thru-beam can be adjusted to ignore residue and detect the product.
I did it many years ago with huge coffee grinders.

Ken,
Is the stuff water soluable or water based? If so, the dielectric should be high enough to work well with radar.

You should be aware that there has been more innovation in the past 4 years in non-contact radar than the previous 20 years combined. So if your radar experience is from 4 or 5 years ago, then current models have significantly better performance than earlier models.
I got a peak at Siemens stuff due out shortly. Signal to noise is far better than previous models.

Ultrasonics won't work in vacuum or varying partial vacuum.

I haven't had enough experience with laser to comment. Have you talked to K-tek?

Dan

what kind of range we are talking about? do you have picture of the product? i've been using analog laser sensors on different kinds of sponge and foam products which ware dry and cool but it seams that your product is "fresh" and bubbling...

I know technology is advancing, so I keep looking. I just finished a 3 month trial of a guided radar unit from Rosemount. This unit will work on the one product you set it up for. But when you run a different product, the foam density changes, and it doesn't detect it. We're one of those just in time operations, so we seldom make the same product back to back, I'd have to re-configure the unit every 4-6 hours around the clock, not an option.

I want to detect the foam, not the liquid underneath. The purpose of the foam detection, is to keep the foam out of the vacuum system. The product is roughly 50% water, so it's very conductive.

I have not looked at infra red, but a through beam isn't an option. The vessel is a closed unit, needed for the vacuum cooling. We usually pull the pressure down to around 3-4 psia.

Laser sound interesting, what are a couple of vendor names?

Ken Moore said:

I have an application where a sticky foamy product is vacuum cooled in a large vertical vessel. I'm currently using two Capacitance probes for high and low with a deadband control scheme. When the high probe is made I kill the vacuum until the low probe breaks.

The problem is that the capacitance probes foul in about 2-3 days, and give false readings. So I'm looking for a different technology. The foam is of variable density. I've tried ultra sound, radar and guided radar, from almost all of the major vendors. I currently trying something similar to the Capacitance that's based on RF Admittance.

I know some of the forum members have experience in waste treatment plants, and may have a better method of foam detection. I'm willing to try almost anything that has some hope of working, and is fouling resistant, non-contact would be ideal.

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WHAT NOT TO USE:
Don't let any sales rep convince you of differential level for your application. Differential only works well when the vacuum is fairly constant and the product's viscosity is constant. I know from expericience trying to measure level in vaccum vessels, that any sudden and rapid changes to the vessel's pressure, throughs the differential out of whack for a period of time.

Ian

well everyone seam to have them nowdays but most of lasers we use are either Baumer, Keyence or IfmEfector.
we use them often because we always get to do crazy things - like measuring distance to something very small (1 or 1.5mm wide), relatively far (like 1..2ft), often at angle, painted black, with black background etc, often looking through small openings, like inside narrow channel, target and background not consistent, possibly contaminated (covered with greese) etc. lasers can do amazing things but they don't do magic...

you will want to test sensor before buying, specially in difficult applications like target surface is not consistent (angle, texture etc.). it's always good idea to invite rep to demonstrate product. Most todays products have very little sensitivity when it comes to target color change but you don't want surprises and don't forget about angle (what is the size and color of foam bubles in your case?).

IfmEfector has O1D100 sensor for example. this thing is unusal compared to the rest - it's much cheaper (some $300US), has prety big maximum range 0.2-10m which can be trimmed down for the application, two outputs (one is digital, the other can be either analog or digital). It is in sturdy metal housing, has display etc. My only complaint is sampling rate, i wish it was faster (it's adjustable 1..50 Hz). Because of low cost, we use it often instead of photoeyes (background suppression etc. because of such long range it is not suitable for detecting things smaller than some 2mm or so (i think that should be good enough). It has bigger mark than most lasers (approx 1.5x5mm), reading of targets that are not perpendicular or have different texture is good. Has nice mounting bracket. This is probably first thing i would try.

When it comes to different applications, I like selection Baumer has. Their sensors are reasonably priced (tipically some 1000-1300USD), compact so can be fitted anywhere. Usually covered ranges are shorter (16...120mm, 50..250mm, 100..500mm, etc.) which makes them perfect for what we do.

Keyence has some of the most accurate distance sensors, great things for lab precision measurement etc. very expensive (usual price range is some 6000..8000USD), bulky, normally come in three pieces (sensing head, control unit and cable that connects them). I would not consider them for your application, just mentioning...

Old thread back from the dead.
Any of you guys know of a good sensor that can detect foam or if the sensor gets wet from the foam it will detect?

Zombie

http://www.charis.uk.com/Foam_Control.htm

http://www.liscotech.dk/en/products/foam-control

http://iainmccurdy.org/diy/forcesensorfoam/

http://www.agarcorp.com/Solutions/FoamDetection.html

http://www.hycontrol.com/docs/105-lm-file.pdf

http://www.dwn.ie/products/documents/VED-STM-x-SB-T-GS-K-DN50-C.pdf

A vibrating fork level switch might work.

TConnolly said:

A vibrating fork level switch might work.

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I know from experience that vibrating fork level switches, will detect milk foam.

I should have been more specific about my needs.
I have a tank that is about 12 inches (305mm) deep and the liquid is about 3 inches (76mm) from the top of the tank in normal running. I need to know if foam gets within 1 inch (25mm) of the top of the tank.

nonuke said:

I know from experience that vibrating fork level switches, will detect milk foam.

Click to expand...

Endress & Hauser Liquiphant

curlyandshemp said:

Endress & Hauser Liquiphant

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Yes. FTL 20

I've had good luck with FTL-20's too.

One water distillation unit that we have uses the current drawn by a defoaming fan inside the vacuum chamber to decide how much defoaming agent to add to the water solution inside the chamber.

More foam = more current