Needed: Ultrasound sensor of high accuracy for specific gravity

I just need to know a few things about what your application and intent.
1) Is the hydrometer measuring the specific density for different fluids or is it more of a determining when enough of a soluble substance has been added to a mixture?
2) Are you allowed to change sensors or sensor types as long as it is non-contact? Or are you locked into a specific sensor?
3) Is the liquid at super low temperature?
Not trying to be nosy, but these are the main factors in determining how the sensor works the way it does and how to optimize it.

Vibrating Tube Densitometers

These devices are suitable for highly viscous liquids or slurry applications. The mode of operation of vibration tube meters is based on the transverse vibration of tubes as shown in Figure 21.10. The tube and the driving mechanisms are constrained to vibrate on a single plane. As the liquid moves inside the
tube, the density of the entire mass of the liquid is measured. The tube length is approximately 20 times greater than the tube diameter. A major design problem with the vibrating tube method is the conflict to limit the vibrating element to a finite length and accurately fix the nodes. Special attention must be paid to avoid any exchange of vibrational energy outside the sensory tube. The single tube has the disadvantage of presenting obstruction to the flow, thus experiencing some pressure losses. The twin tube, on the other hand, offers very small blockage (Figure 21.11) and can easily be inspected and cleaned. Its compact size is another distinct advantage. In some densitometers, the twin tube is designed to achieve a good dynamic balance, with the two tubes vibrating in antiphase. Their nodes are fixed at the ends, demonstrating maximum sensitivity to installation defects, clamping, and mass loading.

FIGURE 21.10

Vibrating tube densitometer. Tube containing fluid is vibrated at resonant frequency by electromagnetic vibrators. The resonant frequency, which is a function of the density of the fluid, is measured accurately. The tube is isolated from the fixtures by carefully designed bellows.

FIGURE 21.11

Two-tube vibrating densitometer. Two tubes are vibrated in antiphase for greater accuracy. Twintube densitometers are compact in size and easy to use.

The main design problems of the vibrating tube sensors are in minimizing the influence of end padding and overcoming the effects of pressure and temperature. Bellows are used at both ends of the sensor tubes to isolate the sensors from external vibrations. Bellows also minimize the end loadings due to differential expansions and installation stresses. The fluid runs through the tubes; therefore, no pressure balance is required. Nevertheless, in some applications, the pressure stresses the tubes, resulting in stiffness changes. Some manufacturers modify the tubes to minimize the pressure effects. In these cases, corrections are necessary only when high accuracy is mandatory. The changes in the Young's modulus with temperature can be reduced to nearzero using Ni-span-C materials whenever corrosive properties of fluids permit. Usually, manufacturers provide pressure and temperature correction coefficients for their products.
It is customary to calibrate each vibration element densitometer against others as a transfer of standards. Often, the buoyancy method is used for calibration purposes. The temperature and pressure coefficients are normally found by exercising the transducer over a range of temperatures and pressures on a liquid with well-known properties. Prior to calibration, the vibration tube densitometers are subjected to a programmed burn-in cycle to stabilize them against temperatures and pressures.

FIGURE 21.11

Two-tube vibrating densitometer. Two tubes are vibrated in antiphase for greater accuracy. Twintube densitometers are compact in size and easy to use.

Below is the link i found. Info is on page 11 of 17

http://www.autex.spb.ru/download/wavelet/books/sen sor/CH21.PDF

Sorry, i copied over the first part of my reply..

Hello, im familiar with hydrometers, however ive only familiar with using the small specific range glass types of hydrometers. Is the section i copied above an adequate representation of your setup? Where does your sensor fit into the setup mentioned above if it is a correct representation?

Thanks :)