Liquid level sensor help!

I am searching for a liquid level sensor that can detect the level of a liquid with foam on top. I want it to detect the liquid but not the foam. I am sure there is a thread already but I haven't found it yet.

Thank you in advance.

Use a pressure sensor.

Could you provid a few more details of the meachanics of the system?

e.g. size, can the fluid be touched, how accurate do you need to be, is the liquid hot, ...

There are many ways of measuring liquids.

Foam and liquid have different physical properties

  • densitiy
  • mass
  • heat transmission
  • electrical conductivity
  • optical transparency
  • sound

Which of them do you think can be exploited best?

A float that is buoyant in water but not foam. Post a drawing of your apparatus.

I am building a beer can filler. A float switch is the easiest solution but space and sanitary concerns eliminate that option. I tried a liquid sensor but as soon as it hits foam it throws a value the same as if it beer.

I started to do some research on pressure sensors but don't know enough about them. I a trying to keep this as simple as possible.

One solution is to not bother about the actual filling level but measure the amount of stuff flowing into the can. Inductive flow meters do not require spinning mechanics in the flow but use the electrical properties (Ions) of the liquid. This way sanitary requirements are easier to achieve, also it does not need to be inside the can.

You could also check out how gasoline pumps stop. There is a sensing tube inside the tube that fills the liquid. While the liquid is filled gas/air flows through the sensing tube. As soon as the liquid reaches the sensing tube it cuts off the airflow and changes the pressure at the end of the sensing tube.

Although the flow meter would measure exactly the amount of beer.... when beer hits the can you have a substantial amount of CO2 breakout(foam). This is different depending on temp, levels of CO2 etc. There are units out there currently using some sort of sensor to tell the filling circuit to stop when beer has reached a given level.

I appreciate the info and its is helpful. Sometimes it is this brainstorming that can take you down a new path to discovery.

The easiest way of measuring while filling is the weight of the can.

As you want to fill cans, that most likely means you have no means of placing anything inside.

Wvmarle, I thought that as well. But then I realized I never saw a fast weight scale. You always have to wait first for calibration and step on it and don't move. And when you are old enough to know mechanical weight scales, they always overshot when you drop stuff in. I suspect the same happens while the liquid flows in. So, while the can is filling, I fear measuring the weight is harder than one would think, especially when you have a lot of cans to fill and you need to be fast.

How about using the optical properties of the liquid? You could measure the light reflected or absorbed by the liquid. Because light can be transmitted through fiber you could remove the electronics from the liquid. You could use a steel tube with a lens at the end with two fibers. One sends light down to the lense and one sends the reflected light back. Once the tip of the tube gets submerged the light reflected/absorbed changes.

That overshoot has to do with the momentum of the material moving down towards the scale, and is in fact a correct measurement. Same for when you move, that indeed changes your weight, and that's what the scale correctly shows. Note: in common parlance we confuse weight and mass all the time... as we're commonly measuring mass by measuring weight.

Load cells are fast; the weight display of the scale is deliberately slow in updating as a human has be able to read them. Humans are very slow in reading compared to computers.

When you are filling cans, I may assume that are lots of the same cans, and tar weight is always the same. That's no issue. Nor is overshoot: as long as the material enters the container at the same speed during filling, the overshoot will also be the same every time. So all you do is fill until a specific weight has been reached, and cut off the valve at that weight - which is simply set to the desired fill weight + tar + overshoot.

Another simple way of filling lots of the same containers is by using time. You know how fast your delivery pump pumps, so open the fill valve for a specific amount of time and a pretty accurate volume will be dispensed.

Weight would be accurate but when you are trying build something with the fastest fills per minute I am not sure it will be the best option. But a viable one.

As far as measuring it by time also an option but with a fluid that foams(CO2 break out) you can not accurately do it just based on time. A can fill set for 10s could produce half a fill in liquid and half in foam. We would need to continue that fill until the liquid pushes all the foam out.

Optical sensors are an option also. I would believe there will be some variables as the liquid isn't all the same color. I could be wrong but just thinking things out as simply as possible.

I do have a working unit with a float switch. Its not ideal and I know the commercially built units use either conductivity(which I haven't figured out how to measure and create an "off" switch) or possibly using pressure(which I am also unfamiliar with). Using a pressure switch will it be able to measure pressure with just a small amount of pressure just touching the top of the liquid?

A dipper of the proper size to fill the beer can might work. The dipper is dipped into the vat, the dipper removed from the vat, a scraper swipes the top of the dipper, the dipper is dumped into the beer can filler unit.

rhorton7333:
I do have a working unit with a float switch. Its not ideal and I know the commercially built units use either conductivity(which I haven't figured out how to measure and create an "off" switch)

Conductivity is simple, as long as you have a good idea on the conductivity of your liquid. A probe of two pins and a pull-up resistor is all you need; no liquid and the resistor pulls the signal high; with liquid it's pulled low by the lower resistance of the liquid.

or possibly using pressure(which I am also unfamiliar with). Using a pressure switch will it be able to measure pressure with just a small amount of pressure just touching the top of the liquid?

You first just asked for liquid level. A pressure transducer in the bottom of the container, or a pressure tube inserted in it, give a very accurate and reliable liquid level. That's not suitable for a can filling device.

A pressure switch may work but I doubt it's reproducible enough: you want to have it switch at a very specific weight, so as not to overflow or underfill your containers.

Thats the answer. Conductivity! Now I have to teach myself how to do all this Arduino programming to be able to measure all that! Given the fact that beer/cider all have different degrees of Plato(measuring sugar levels). Really we are measuring the difference between foam and liquid.

Sugar is not conductive. Salts (ions) are.