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State standard of the republic of uzbekistanBog'liq 27608-разблокирован DALINA, Abdulla Qahhor. Paqir qo\'mondonlariISO 27608:2010(E)
© ISO 2010 – All rights reserved
3
7.2 Samples
requiring
heating
Solid samples, such as fats and tallow, require some form of heating. If the prepared sample is not fully liquid
at room temperature, heat it to a temperature approximately 10 °C above its melting point.
IMPORTANT — The sample shall not be heated to the extent that it becomes scorched or discoloured.
Stirring the sample in a heated cell prior to measurement can help to disperse thermal currents or bubbles and
establish a uniform temperature throughout the sample. The temperature at which the colour measurement is
carried out should be recorded in the test report for all samples.
7.3 Filtration
If turbidity is present after heating, the sample shall be filtered to an appropriate level. It is, however, advised
to filter all samples prior to testing as slight turbidities are difficult to see with the naked eye. The filtration
process shall not affect the colour of the sample.
NOTE
Suspended material and bubbles, even if of colloidal size, cause light scattering and can result in inaccurate
measurement results.
8 Procedure
8.1
Position the automatic colorimeter on a stable surface and ensure the following:
a) the unit is away from bright, direct sunlight;
b) the ambient temperature is between 0 °C and 40 °C;
c) a regulated power supply is available.
8.2
Turn on the colorimeter and allow for initialization to be completed (refer to manufacturer's instruction
manual).
8.3
Select the Lovibond
®
colour scale from the menu options.
8.4
Select or input the required optical path length.
8.5
Perform zero (baseline) calibration according to manufacturer's instructions. This calibration should be
performed at regular intervals depending on instrument usage.
8.6
Measure at least one certified glass or liquid reference standard (5.2) to verify the performance of the
colorimeter prior to sample measurement. It is recommended that any glass reference filters be re-certified
regularly and that the shelf lives of liquid reference standards be observed.
8.7
If an integrated heating system is available on the instrument, set the heater controller to the required
temperature. This is generally 10 °C above the melting point of the fat. This allows a constant sample
temperature for the duration of the measurement (refer to manufacturer's instruction manual).
8.8
The optical glass cell (5.3) shall be thoroughly clean and dry and, if necessary, pre-warmed to the same
temperature as the sample so that no solid matter separates from the sample during the colour determination.
If heat loss occurs, re-heat the sample and cell simultaneously.
8.9
Pour the liquid sample into the cell. It is recommended the cell be filled except for the top 3 mm. The
optical path length of the cell used should be related to the colour saturation of the sample. Reduce the path
length if required. It is advisable to restrict the colour intensity of the sample to a maximum of 4 Lovibond
®
red
units for optimum colorimeter performance. Using a shorter path length cell, or equivalent, reduces colour
saturation and increases measurement precision. Trade contracts, however, often prescribe fixed cell lengths.
O‘z DSt ISO 27608:2017 (ISO 27608:2010, IDT)
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