The principle of a digital density meter is that an object’s gravity pulls the object toward the ground, but if the object is placed in a liquid, a force called buoyancy will create a force in the opposite direction. The magnitude of buoyancy is equal to the gravity of the liquid the object displaces, or the gravity of the water displaced.
Densitometers float or sink according to changes in the balance of gravity and buoyancy. A fully functioning densitometer can only float, so buoyancy pushes up slightly more than gravity pulls it down.
the principle of digital density meter
Because the volume of the density meter does not change, the volume of water it drains is the same. However, it becomes heavier because it contains more water. When gravity is greater than buoyancy, the density meter sinks. The weight of the density meter is less than the weight of the same volume of water, so the density meter refloats. The reading of the density meter is big at the bottom and small at the top. When it is immersed in different liquids, the volume does not change and the indication changes. The iron sand or lead particles at the bottom of the density meter are used to maintain balance!
The density meter reading is large and small because P=ρgh, the deeper the density meter enters the liquid, the greater the pressure, so the density meter reading is large and small.
Types of Digital Density Meters
Commonly used density meters and hydrometers are float type density meters, static pressure type density meters, vibrating type density meters and radioisotope density meters.
The working principle of the float density meter is: the buoyancy of the object in the fluid is related to the fluid density. The greater the fluid density, the greater the buoyancy.
The working principle of the static pressure density meter is: the static pressure of the liquid column at a certain height is positive with the density of the liquid, and the specific gravity value can be used as the scale value. The simplest of these instruments is the visual float glass hydrometer, or glass hydrometer for short.
The bellows is a commonly used pressure measuring element, and the density meter that directly measures the static pressure of the sample liquid column is called the bellows static pressure densitometer.
Another commonly used one is the single-tube blowing density meter. It measures the air pressure instead of directly measuring the liquid column pressure. Insert the air blowing pipe into a certain depth below the liquid surface to be tested, and the compressed air will continuously escape from the bottom of the pipe through the air blowing pipe. At this time, the pressure of the air in the tube is equal to the pressure of the sample liquid column at that height, and the pressure value can be converted into density.
Two Austrian scientists, Hans. Stabinger and Hans Leopord, discovered the measurement principle of the oscillating tube densitometer: when an object is excited and vibrates, its vibration frequency or amplitude is related to the mass of the object itself.
If a U-shaped glass tube is filled with a certain volume of liquid sample, the change of its vibration frequency or amplitude will reflect the mass or density and specific gravity of a certain volume of sample liquid. The two scientists later designed a prototype and handed it over to Urich Santner and his company Anton Paar to design the first digital liquid density meter in 1967. At present, the fully automatic liquid density meter is based on the principle of U-shaped oscillating tube.
The radioisotope densitometer is equipped with a radioisotope radiation source. Its radioactive radiation (such as gamma rays) is received by the radiation detector after passing through a certain thickness of the sample to be tested. The amount of radiation absorbed by a sample of a certain thickness is related to the density of the sample, and the signal of the radiation detector is related to the amount of absorption, thus reflecting the density of the sample.
