bubble detecting sensor.

Red wine or white?

Idealy it would work with both, but at the moment that isn't a huge concern. More interested in the type of sensor required. So doesn't really matter whether red or white. I would assume white wine would be harder though.

You could try using a laser pointer shining through your clear tube at an angle, onto a surface a few inches away. See if the spot on the surface shifts when a bubble is in the laser beam. If it does shift, then a simple light detector at the spot location will detect the bubble.

Another method is to put small metal plates on each side of the tube - the capacitance between the plates will change when there is a bubble between the plates. You can buy commercial sensors that use this principle.

Newark/element14 carry several Optek optical sensors that can detect liquids in tubes for $5 - $8.

such as:

OPB350 OPTEK TECHNOLOGY Liquid Level Sensors - Optical | 73H3201 | Newark element14 Canada

Starting out, let's freely ideate:  Aluminum foil is dynamically gauged by using radiation.  We could put a Geiger/Muller counter/detector on one side of your tube and a source on the other. . .

Actually not being silly, this works great and isn't that hazardous because the detector is so sensitive.

I wouldn't write an acoustic sensor off the table.  The tube may be less rigid when empty.  This would lower its resonant frequency, for example.

Presuming your tubing is clear, we can differentiate between white wine and air using the difference in refractive index, probably.

We need data my friend.  One thing is if white wine isn't clear in the near IR or near UV we are home free.

I would take Douglas's sensor and hook up a good amplifier to it.  The sensor, IIRC has a logarithmic characteristic and may need to be linearized with an antilog amplifier for greatest sensitivity.  The loss characteristics might be different enough to reliably detect in the case of white wine versus air.

Why are you getting bubbles?  Are you using a siphon?  Peristaltic pump?

Hi Kurtis  You might want to consider using a sensor that puts a  light signal on one side of a clear line and an analog light sensor on the other side of the line. A few inches down the hose you put a second identical light and sensor. The outputs of the two sensors are then subtracted from each other. This will give us zero output whenever the solution is consistent. It will not matter if the solution is red or white as long as it is transparent or translucent. When an air bubble comes along there will be a difference in the two sensors and the subtraction will no longer equal zero. This will be your trigger to indicate an air bubble. If the sensors mentioned by Doug, with the link, are available in the hose size that you use they may work well for this technique with the right circuitry. If the hose size is different you could make some custom sensors. I suspect that you could use Infra Red sensors as typically there is less absorption of long wave lengths in a medium but I am not sure. I understand the physics of this approach but I do not have enough specific electronics experience to give you good guidance on the selection of components or circuits. If I were to try to design this sensor I would have to get some LEDs and a variety of sensors and start experimenting to see if I could produce a measurable sensor event with bubbles. I will continue to think about this problem and post again if any other ideas come to mind.

John

Thanks for all the input guys! what an awesome community this seems to be!

There are bubbles in the line because we are using nitrogen to displace wine in a bottle (to avoid oxidisation) however when the wine bottle empties the gas is pumped through the line and heart exchange. Hence we want to minimise gas in the line.

The solution I've been experimenting with today involves two electrodes either side of the line immersed in the wine. When there is wine flowing through, the circuit is complete, when there is no liquid, no circuit. Then we just need a relay or something which can activate the gas on/off switch.

Hi Kurtis.

You could also consider using an ultrasonic sensor. An ultrasonic sensor working in the 1MHz to 5 MHz range would be good at detecting bubbles. The acoustic impedance mismatch between the bubbles and the surrounding liquid (wine) will ensure good reflectivity.

Regards

John Norman

Hi Kurtis - You may want to consider that if you put over 1.23 volts of voltage across the wine you will electrolyse the water molecules and create a bubble of hydrogen and oxygen at your sensor site. This process will be accelerated if you are trying to run a relay directly as the current involved to close a relay is fairly high. If you can use the electrode sensor to control an E MOSFET or an OP amp that in turn controls the relay at least your hydrogen and oxygen production at the site will be held low. From a stand point of not messing electrochemically with your product a non-invasive processes of sensing the bubble as mentioned by Don or Doug or John's ultrasonic might be preferred.

John