Sensing Foam?

[Mac 1]

Hello Everyone. I was wondering if anyone has ever tried to sense foam before? We are in a situation where we have a Large Wash Machine with a "soapy" cleaning agent that sometimes foams up a little too much in the process if it is not monitored by the operator. If anyone has come across this type of situation I'd like to hear from you! I'm looking to use Allen Bradley or Omron sensors if possible but I'm open to anything. Any help would be appreciated. Thanks

[DanW 41]

A serious drawback to most top-mounted ultrasonic level sensing is that the ultrasonic beam bounces off the foam so the signal indicates the foam or part-way through the foam level, not the liquid level beneath the foam, which is what most people want to measure. Top mounted Radar level faces much the same difficulty. Part of the problem is in classifying the foam. Some foam is very dense, other foam is very 'light', almost like the bubbles kids blow with soapy water and a wand with circular ring. I'd suggest asking a level distributor who handles level if you can try an ultrasonic unit and see if the signal bounces off the foam and gives you what you want. Milltronics (now Siemens) used a mechanical float to get the liquid level and the ultrasonic to get the foam level for a mining application where the foam was really dense, always present and the ultrasonic signal always bounced off the top. With both signals, the DAQ system could dislay liquid level, foam level and foam height. Dan

[P Daniil 0]

A capacitive level sensor should do it. What kind/chemistry of "soapy" foam is it?

[Ken Moore 23]

I've been trying to reliably detect foam for over a decade. If your foam is always the same, then you can fine tune the radar devices to work, guided is best. If your foam varies, no joy. I have found that capacitance probes work best, but in my case the liquid coats the probes and we get a false positive after a couple of days. This caused me to try out radio admittance probes, they work similar to cap. probes but are more fouling tolerant. I've had good success with Drexelbrook devices. http://www.drexelbrook.com/products/produc...Product_Id=1031

[TimWilborne 108]

Ok, kind of along the same lines, how about reliably detecting the foam at all? I just was at an application yesterday that is mainly concerned with the liquid level in the tank which can easily be accomplished with a pressure sensor, but they also don't want to overflow the tank with foam. Any ideas for a high high foam detector?

[Ken Moore 23]

If the foam is conductive the capacitance or RF admittance probes work well. Clean service = capacitance Dirty service = RF admittnace I've been using the RF devices in our Waste treatment plant, so far, so good.

[TimWilborne 108]

This is on a waste treatment system. The problem I have ran into with this one is that the waste stream, along with the foam, varies tremendously. Some days it is light and fluffy, other days it has a crust thick enough for my laptop to float on. I'll look into the RF Admittance probe

[Ken Moore 23]

The RF devices are extremely fouling tolerant, they usually work until the build up on the probe looks like a Hornet's nest. Then just hose them off and you're good for another few weeks.

[TimWilborne 108]

And you don't have any echo problems with them?

[Ken Moore 23]

Echo?

[TimWilborne 108]

Signal shooting down, hitting the foam, and going in 75 different directions. Problem with the ultrasonics. I'm leaning towards telling them to run their tank at 75% capacity and sticking a pressure sensor in the bottom of it. Looks to me like the tank is plenty big and the foam doesn't seem to get over a couple feet thick.

[Ken Moore 23]

I have one sump that always has a foaming problem, we use a DP cell to determine liquid level, this starts/stops pumps as needed. However, like your application, sometimes we have foam several feet, sometimes only a few inches. The RF probe is used outside the PLC logic, I'm using the onboard relay contacts to sound an alarm in the control room, (has a hardwired ack button). When the alarm sounds the operators goes out and adds defoamer to the sump. Prior to the probe addition, we often got foam coming out the top, and the wind carried it to a neighbor's house, not good.

[TimWilborne 108]

Sounds like another company I know, they put it in the budget every year to repaint one lady's house

[DanW 41]

Waterbug made by Winland Electronics. Plastic housing looks cheap, (was an issue with one Pharma customer), but works OK by sensing conductivity of water on the that contacts its bottom mounted sense strips. Dry contact output. Winland Electronics, Inc. 1950 Excel Drive Mankato, MN, 56001, U.S.A. Phone: (507) 625-7231 Fax: (507) 387-2488 www.winland.com

[TimWilborne 108]

So they work off of conductivity, do you think that would be a problem with high purity water?

[Ken Moore 23]

What do you mean by high purity? Distilled?

[DanW 41]

Yes, unless the floor is dirty enough to add something conductive to the water. I suspect that it wouldn't work in "Bunny suit" clean rooms..

[TimWilborne 108]

First I've gotten off subject here, high purity water doesn't have a foaming problem. High purity is actually a generic term and will depend on the customers specifications, but by definition high purity water will have a conductivity of 0.055 S.cm–1 or a resistivity of 18.18 M?.cm. Many times the conductivity requirements will not be that high, but they I have done some applications that were

[Sleepy Wombat 27]

TW is talking about deioniosed water. (i think) Yes, I believe that they would have problems with high purity water. (My original back ground was from industrial water treatment ie demin plants, mixed bed;s, cmf, RO;s etc) Hopefully you can have a bund area with a float switch.

[DanW 41]

I've been wracking my brain about how to sense the presence of water without using conductivity. I recall running into a refractive index point level switch once. It was designed to mount into the side of tank. When the liquid level covers the sensor, there was a distortion of the source light beam by refraction, and through some means the sensor detected that and switched states. I'll poke around and see if I can locate that device to see what sort of installation options it might hvae, other than threaded-hole-insert. Dan

[TConnolly 13]

Sometimes the solution (pun intended) to a problem may lie in a different direction. Right now we don't know a lot about the OP's process, but this sentence is what caught my attention. It implies to me that there is somthing the operator can do to prevent foam, but that sometimes he/she is distracted. What is it that the operator does to prevent foam in the first place, and is that what should be automated instead? Have you investiaged anti-foaming additives?

[Ken Moore 23]

Here's a snippet on RF probes.

[TimWilborne 108]

Wow, from what I am reading that should work great in the sludge tanks