DIN 12791-1:2011-01

Hydrometers are special precision instruments for the determination of density of liquids. The standard specifies requirements for five basic series of glass density hydrometers with incorporated thermometers, that is thermo hydrometers, or without incorporated thermometers displaying the density in kg/m³ or g/ml at 20 °C. Any of these series contains hydrometers with a total measuring range of 600 to 2 000 kg/m³ (0,600 to 2,000 g/ml). The hydrometers are adjusted for determination of density of liquids with low, medium and high surface tension. Furthermore, three subordinate series are described where the reference temperature is 20 °C or 15 °C. They have tighter error limits and are limited to the range of 600 to 1 100 kg/m³ (0,600 to 1,100 g/ml). With respect to the previous standard DIN 12791:1981-10, the following changes have been made, in order to achieve a better content-based consensus with the International Standards ISO 387 and ISO 649-1: a) graduation value in Table 2 for hydrometers S 50 and S 50 Th has been corrected to 2 kg/m³; b) error limit in Table 4 for hydrometer S 50 Th has been corrected to 2 kg/m³; c) errors have been corrected in the text of Annex A; d) the standard has been editorially revised in accordance with DIN 820-2. The standard has been prepared by Working Committee "Aräometer" ("Hydrometers") (NA 055-01-01 AA) of the Laboratory Devices and Installations Standards Committee (FNLa) and will be published in agreement with the Physikalisch-Technische Bundesanstalt (national metrology institute) PTB.