What Is a Densimeter?
Specific gravity is the ratio of the mass of a specific substance compared to a standard substance of the same volume.
A densimeter is a device used to measure specific gravity. The term specific gravity is used for solids, liquids, and gases, but this article describes a device for measuring the specific gravity of liquids.
First of all, to summarize the buoyancy force acting on an object, if the specific gravity of water is 1, the object will sink if the specific gravity is greater than 1, and float if the specific gravity is less. The most common type of densimeter that utilizes this principle is the buoyancy scale.
This is a scale that floats on a liquid, reads its scale, and measures the specific gravity based on the value of the scale.
Recently, however, load cell, vibration, differential pressure, and radiation types are also available, and products with digital displays that make measurement easier than conventional ones have been developed.
Uses of Densimeters
Densimeters are used in a wide variety of applications in fields such as pharmaceuticals, food processing, industry, and scientific research.
Specifically, they are used in the following areas
- Measuring the salinity of seawater
- Measuring the sugar content of fruits used to make juice
- Measuring the concentration of various chemical solutions used in industry, such as semiconductors, plating, and battery electrolytes
- Measurement of fat content in milk
- Determination of alcohol content by volume ratio of water in alcoholic products
- Measurement of impurity content in petroleum products
Principle of Densimeters
The basic structure of densimeters are shown in Figure 1. The body maintains buoyancy, and the meter is scaled.
The bottom of the body contains a weight for buoyancy adjustment. When the body is placed in the liquid to be measured, the buoyancy of the scale is equal to the weight of the volume of the liquid in which the scale is submerged.
As a result, the scale sinks into the liquid to the extent that its own weight is balanced by the buoyancy force. The scale is graduated, and when the buoyancy of the scale reaches equilibrium, the reading on the scale coincides with the surface of the water.
Most hydrometers are made of glass, but plastic hydrometers are also available.
Other Information on Densimeters
About Densimeters Other Than Hydrometers
In addition to hydrometers, there are other types of densimeters such as load cell, vibration, differential pressure, and radiation densimeters, which are mainly used in the industrial field.
A load cell is a machine that converts the magnitude of force into an electrical signal, accurately measures the weight of a weight submerged in a liquid, and calculates the specific gravity of the test liquid from the amount of change in the load.
This type of densimeters has the advantage of higher measurement accuracy than conventional hydrometer-type densimeters and of making it difficult for differences in the analyst’s technique to affect the analysis results.
In the case of the vibration type, test liquid is injected into the U-tube, and the U-tube is vibrated from the outside. At this time, the U-tube vibrates at a frequency specific to the mass of the entire U-tube, including the liquid content. Therefore, the mass of the liquid inside the U-tube can be calculated from this frequency, and the density of the sample can be calculated from this value. This type of densimeters are widely used for quality control, especially in the food industry, because it is intuitive to operate and measurement can be completed in a short time.
The differential pressure type uses the principle that the difference in pressure between two points on a measuring row is proportional to the specific gravity of the liquid. The radiation type uses the property that the transmittance of gamma rays emitted from radioisotopes varies with the density of the material.