Applying the Archimedes principle-gas expansion displacement method, using the inert gas of small molecular diameter under certain conditions of Bohr's law (PV=nRT), by measuring the sample test chamber gas caused by placing the sample in the sample test chamber The reduction in capacity is used to accurately determine the skeleton volume of the sample (including closed cells) to obtain its true density, true density = mass / skeleton volume. The gas expansion displacement method is a volume in which a sample is discharged by measuring a liquid by a gas. This method eliminates the possibility that the immersion method dissolves the sample and has the advantage of not damaging the sample. Because the gas can be incorporated into the tiny pores in the sample and the irregular vacancies on the surface, the measured sample volume is closer to the skeleton volume of the sample, which can be used to calculate the density of the sample, and the test value is closer to the true density of the sample. The test system of the instrument consists of a sample test chamber and a reference chamber, as shown in the figure. When measuring the sample density, the instrument automatically collects and records the pressure P1 and the volume V1 of the reference cavity; puts a sample V of a certain unknown volume into the sample test cavity of the known volume V2, injects a certain amount of gas into the reference cavity and records the stability after recording. Pressure P2; connect the sample test chamber to the reference chamber and record the stabilized pressure P3. According to the equilibrium stabilized pressure value and the relevant known volume V1, V2, the sample volume V sample to be tested can be calculated, and then The true density of the sample is calculated from the mass and volume of the sample. 3H-2000TD series automatic real density analyzer adopts the most advanced air control valve control structure in the industry (patent acceptance number.8), which fundamentally completely eliminates the heat generated by the electromagnetic valve caused by the electromagnetic valve of similar instruments. The problem of volumetric quantitative error. 3H-2000TD series automatic real density analyzer has advanced "bottom mount type" sample cell installation method (patent acceptance number.5), and the sample pool is directly used as sample test chamber, which has the sample chamber volume utilization rate. High advantage; for a 10ml sample cell, the test chamber volume utilization is higher than 90%; thus the test accuracy for a small number of samples is improved; and the usual sample cell "top mount", the sample pool is loaded into the test bucket After the inner cap is sealed and tested, the sample test chamber consisting of “test bucket + sample cell” has a large amount of unused space in the test chamber, which makes the test chamber volume utilization low. For the 10 ml sample cell, the test chamber volume utilization is less than 10%. This makes it difficult to guarantee the accuracy of testing for a small number of samples. On the other hand, the volume of the “top-loading and capping” sample cell is limited by the volume of the covered test drum, and it is not suitable for large-volume loading (it is difficult to meet the loading of more than 150ml volume), and the “bottom mount type” The sample cell can meet the needs of large-volume loading, and the upper limit of loading can reach more than 500ml, so as to broaden the test range, expand the applicable surface, and improve the test accuracy.