Density Sensor - specific gravity

Hey guys!

I desperately need your help and expertise. I’m working on a project where we automatically need to measure the urine specific gravity. These kind of tests basically compare the density of urine to the density of water. It would be possible to use refractometers, but we are looking for continuous measurement with a small device.

  1. Is there some kind of density sensor available?

  2. Does anybody know a workaround without a density sensor? Pressure? Volume?

Any feedback is very much appreciated.


How about measuring the speed of sound with ultrasonic transducers? That will change depending on the density.


I used to work in a lab, and we used a device with an oscillating u-tube (made of glass, perhaps 1mm id) to measure density with very good accuracy, up to 5 or 6 decimals if i remember correctly. I never looked into the details of how it worked but thanks to russellz i suppose it measured the velocity of ultrasonic vibrations. I remember that for very viscous samples you had to correct for the viscosity but for water this was completely negligible. It is probably quite possible to build one on the cheap if you're so inclined, otherwise there's bound to be a second hand market for those machines, accurate density measurement is kind of a basic lab service.

Viscosity and density are two different factors.
I would think that sound is not as good as weight.
How small a volume are you talking about?