Digital density meters (specific gravity meters) use a U-shaped hollow glass tube, which is put into oscillation. The oscillation frequency of the tube filled with the sample is measured. This frequency changes when the tube is filled with the sample: the higher the mass of the sample, the lower the frequency. This frequency is measured and converted to density. In addition, benchtop digital density meters use a built-in Peltier thermostat to control the temperature of the sample.
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