A sample to be measured is placed in a medium solution between two circular magnets to ensure that the sample to be measured is levitated in a set circular area between the two circular magnets, and a levitation position of the sample to be measured in the magnetic field is measured. The density of the sample is calculated according to formula (I):

[00001]${}_s={}_m+\frac{{}_m-{}_s}{g_0}\left(B_r\frac{B_z}{r}+B_z\frac{B_z}{z}\right).$

Compared to the prior art, the method of the present disclosure provides a novel method for measuring a density of a substance, in which the involved device is easy to operate and has low cost, and the measurement results are easy to observe and have high accuracy.

Subsea equipment-protection apparatus including a fluid monitoring apparatus for detecting a first fluid, a second fluid and a third fluid. The fluid monitoring apparatus including a first float having a density less than that of the first fluid but greater than that of the second fluid; a second float having a density less than that of the second fluid but greater than that of the third fluid; and a sensor configured to detect the first and second floats so that the position of the floats can be determined. The first float floating when a fluid with density greater than the first float is present and sinking when a fluid with density less than the first float is present. The second float floating when a fluid with a density greater than the second float is present and sinking when a fluid with a density less than the second float is present.

Subsea equipment-protection apparatus including a fluid monitoring apparatus for detecting a first fluid, a second fluid and a third fluid. The fluid monitoring apparatus including a first float having a density less than that of the first fluid but greater than that of the second fluid; a second float having a density less than that of the second fluid but greater than that of the third fluid; and a sensor configured to detect the first and second floats so that the position of the floats can be determined. The first float floating when a fluid with density greater than the first float is present and sinking when a fluid with density less than the first float is present. The second float floating when a fluid with a density greater than the second float is present and sinking when a fluid with a density less than the second float is present.

Systems and methods for determining fluid density include receiving calibration data for a fluid density measurement tool. The fluid density measurement tool can include a cantilever beam and at least one strain sensor that is coupled to the cantilever beam. The cantilever beam can be housed in the fluid density measurement tool and is buoyed by a fluid that enters the fluid density measurement tool. The systems and methods measure strain values at the at least one strain sensor and determine a density of the fluid based on the calibration data, and the strain values measured at the at least one strain sensor.

Systems and methods for determining fluid density include receiving calibration data for a fluid density measurement tool. The fluid density measurement tool can include a cantilever beam and at least one strain sensor that is coupled to the cantilever beam. The cantilever beam can be housed in the fluid density measurement tool and is buoyed by a fluid that enters the fluid density measurement tool. The systems and methods measure strain values at the at least one strain sensor and determine a density of the fluid based on the calibration data, and the strain values measured at the at least one strain sensor.

A specific gravity measurement apparatus has a specific gravity hydrometer that carries a codestrip at the top. A linear optical encoder is disposed to view the codestrip and to output electronic signals that are indicative of a movement of the codestrip relative to said encoder. The movement is indicative of a change in the specific gravity of the liquid, such as a change in a salinity of the aquarium water in which the hydrometer floats. The measurement apparatus may be incorporated into a saltwater aquarium salinity control system where an electronic controller uses the measurement inputs to control a plurality of pumps for selectively adding saltwater or freshwater to the aquarium water in order to control the salinity of the water at a given setpoint level.

A specific gravity measurement apparatus has a specific gravity hydrometer that carries a codestrip at the top. A linear optical encoder is disposed to view the codestrip and to output electronic signals that are indicative of a movement of the codestrip relative to said encoder. The movement is indicative of a change in the specific gravity of the liquid, such as a change in a salinity of the aquarium water in which the hydrometer floats. The measurement apparatus may be incorporated into a saltwater aquarium salinity control system where an electronic controller uses the measurement inputs to control a plurality of pumps for selectively adding saltwater or freshwater to the aquarium water in order to control the salinity of the water at a given setpoint level.

An automatic liquid density measurement device includes a receptacle configured to contain the liquid, a float configured to be submerged in the liquid when it is contained in the receptacle, and an electronic system. The electronic system includes a first electromagnetic sensor configured to make a reference measurement relative to the electrical properties of the liquid, a second electromagnetic sensor configured to make a measurement of the volume of the liquid displaced when the float is submerged in the liquid, and an electronic circuit coupled with said first and second electromagnetic sensors to determine the density of the liquid based on the measurement of the physical properties of the liquid and the measurement of the volume of the liquid displaced.

A method for determining the amount of a gas present in a battery cell, whereby the battery cell has an initial volume, comprises at least the following steps: a) immersing the battery cell into a non-conductive liquid having a defined density at a first ambient pressure; b) generating a lifting force that acts in the opposite direction of a downforce of the battery cell; c) changing the first ambient pressure to a second ambient pressure, and measuring the buoyancy forcewhich is dependent on the ambient pressureof the battery cell in the liquid; and d) measuring the amount of gas present in the battery cell, taking into account the first and second ambient pressures, the buoyancy forces ascertained for these ambient pressures, the temperature of the non-conductive liquid and the density of the liquid.

A method for determining the amount of a gas present in a battery cell, whereby the battery cell has an initial volume, comprises at least the following steps: a) immersing the battery cell into a non-conductive liquid having a defined density at a first ambient pressure; b) generating a lifting force that acts in the opposite direction of a downforce of the battery cell; c) changing the first ambient pressure to a second ambient pressure, and measuring the buoyancy forcewhich is dependent on the ambient pressureof the battery cell in the liquid; and d) measuring the amount of gas present in the battery cell, taking into account the first and second ambient pressures, the buoyancy forces ascertained for these ambient pressures, the temperature of the non-conductive liquid and the density of the liquid.