volume change sensors

[squir999]

i'm looking for sensors that can measure volumetric change to within 1 cc accuracy. if anyone knows of websites or companies from which i can get information about this that would be great.

thanks!

 

[zeitghost]

1cc in what sort of volume?

 

[itsmoked]

As far as I know there is NO SUCH ANIMAL.... How could it even work? I would expect either strain gauges or level sensors applied to the shape or tank respectively. Hence distance measurements used to calculate volumes.

 

[VEBill]

Mr. Smoked is correct - volume is not a fundamental property in the same way as mass, length, etc. There is no standard One Cubic Meter in a vault in Paris in the way that there is with mass. You need to measure something else and the calculate the volume.

What else to measure depends on the application.

 

[squir999]

I suppose I should have been more specific. Sorry about that. I know that volume is not a fundamental property, and that the sensor would be measuring some fundamental property and then using that to calculate the volume. However, the specifications for the project are for measurement (or calculation) of a volume (about a gallon of total liquid) and any changes in that volume, with an accuracy within an 1 cc.

 

[itsmoked]

Fess up what kind of liquid? Aqua Regia? Gasoline? Ether? Methamphetamine? Lava? Napalm? This makes a difference in what we suggest you know...

 

[VEBill]

Assuming that you're in a gravitational field and using an open topped container - the liquid will change level in only one dimension (depth). Make the container tall and skinny to magnify the depth changes and it becomes a very simple problem. Make the container a square meter in surface area, and it becomes very difficult to detect a 1 cc change. Likely you'll need to measure the distance to the top surface from above using an off-the-shelf but expensive sensor.

You could also weigh it to the nearest gram (+/- density).

You could toss a pressure sensor into the depths (tall container better).

You could let it swing and measure the period.

Acoustic resonance in a partially submerged tube where the note is set by the fluid level at the bottom. That one might actually work pretty good...

This reminds me of the old joke about using a barometer to determine the height of a building. You offer the lovely and expensive barometer to the building's caretaker if he will just tell you how tall the building is.

 

[squir999]

Lol. Thanks for all of this, it was somewhat helpful. Btw, the liquid in question is just boring old water. :/

 

[squir999]

We may use this sensor to measure other liquids too, such as oil. But that is much later down the line.

 

[itsmoked]

Ah, then there are just more sensors available.

Ultrasonic to the surface.
There are resistive ones.
Tuning fork may work in your app
RF Capacitive sensors.


But WOW! 1 cc out of a gallon is not going to be easy! You are talking about 2 hundredths of a percent!!

Say you poured your gallon into a tube to magnify the level change as VE1BLL suggests. Say the tube is 1 inch in diameter. Your column would be 294.267 inches tall(24.5 feet!) Now a one cc increase of this liquid would represent a column height change of 0.078 inches.

This is why no one does this.

How would you even know if you have an *exact* gallon to begin with?

Your only hope is to find something that does indeed measure the density of the water. Say a vibrating structure whose frequency changes with water density. Or an optical effect. Or measure a bulk capacitance change in the water.


The pressure sensor method may not actually work since the water column would get deeper but the water would be lighter. EEEEW!

 

[IRstuff]

Well, it's still unclear what the volume change comes from and what the intended usage is.

You could quite easily conceive of a 1 gallon-20cc container with a 40cc syringe tube at the top and you'd be able to measure 1 gallon to better than 0.25cc.

TTFN

 

[squir999]

Thank you all so much. This gives somewhere to begin. I really appreciate it.

 

[xnuke]

If your container is closed and at constant temperature, you could admit a known quantity of air and measure the pressure that results. With good control over flow and measurement of pressure, a pretty accurate measurement would result.

xnuke
"Do you think you used enough dynamite there, Butch?"
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tofflemire]

Hi Squir999,

I would try and isolate you level detector from the main tank. Can you add a calibrated cylinder to the side of the main tank, and have your sensor measure this alone. You could install a pressure sensor on this cylinder with very fine divisions; you should always have the same starting pressure assuming you put in the same amount of water.


Tofflemire

 

[Compositepro]

The measurement can be made very easily and accurately. A mercury thermometer is one example. A gallon jug with a stopper and a straw will also work.

 

[itsmoked]

Compositepro you forgot something.

[A gallon jug with a stopper and a straw]

And a human.

 

[Compositepro]

The suggestions were as detailed as the defined requirements, but were really intended inspire some imagination in the responses. If squir999 is looking for a turn key instrument, and has the money, Dynatrol and Paar (

http://www.anton-paar.com/ap/apinternet/html/default/cxsn-5quk94.us.0)

make vibrating U-tube density meters with sensitivity of 1 E-5 g/cm3. Hydrometers with large floats and narrow measuring necks are much cheaper and there are instruments that use the same measuring principle and put out a signal according to the height of the float. A difficulty with any density measurement is bubbles and dirt build-up.

 

[itsmoked]

Ah now that's some interesting stuff.
"oscillating U-tube principle" Most interesting.

I would go with a density-meter method before trying to monitor the exact physical volume because the measured volume would no longer matter.

Thanks.