AS 2026:2003 pdf – Laboratory glassware-Density hydrometers

AS 2026:2003 pdf – Laboratory glassware-Density hydrometers.
AS CORRECTIONS TO TIlE READING
AS.1 Instrument error
Instrument error is the difference between the reading of the hydrometer and the reading of an ideal hydrometer under identical conditions. Corrections for instrument error may be applied under all conditions of use. additional to other corrections such as those for temperature and surface tension which vary according to conditions of use. For many purposes it is sufficient to know that the instrumental error does not exceed the maximum permitted error given in Clause 12. In this case the scale of the hydrometer should be appraised as follos:
(a) The linear dimension should be checked with a suitable graduated steel rule and outside micrometer callipers to verify that it complies sith the requirements of Clause 9.
(b) The scale of a hydrometer of the L20. L50 and L5OSP series should he calibrated on at least five points within the nominal limits, which should include at least 80 percent of the graduated interval of the scale.
Neither of the extreme points should he further from the nearest end of the graduated scale than a distance equal to 15 percent of the graduated scale.
No two adjacent points should be further apart than a distance equal to 25 percent of the graduated scale.
(c) The scale of hydrometers of all other series should he calibrated in a similar way following the same order as in Step (b) hut at three points, which should include at least 60 percent of the graduated interval of the scale.
Neither of the extreme points should be further from the nearest end of the graduated scale than a distance equal to 25 percent of the graduated scale.
No two adjacent points should be further apart than a distance of 50 percent of the graduated scale.
(d) The position of the scale should he checked regularly to verify that there has been no displacement of the scale since manufacture. Testing the hydrometer at one point will serve this purpose.
,5.2 Temperature correction
If the reading is made at a temperature other than the reference temperature of the hydrometer. apply the temperature correction for the change in volume of the hydrometer between the tso temperatures given in Table Al.
It is important to realize that the corrected value is the density of the liquid at the temperature of observation and not that at the reference temperature.