Considerations must include:
• The analyser should be installed in the mixed
section of the blend. If it is not then the analyser
will NOT give representative measurements.
• The blend mixing system should be efficient
throughout the complete flow range of the
blend and not create too much pressure drop to
inhibit the high flow rate.
• If the analyser incorporates a referral process in
conjunction with line measurement and line
temperature, such as referring viscosity at line
conditions to 50º Celsius, then:
(i) The referral method should suit the
temperature and dynamic measurement
RANGE being taken. Most analysers only
employ one ASTM or matrix curve to refer the
line measurement to a standard temperature.
This method is normally unacceptable as it
assumes that the viscosity is constant and that
only the temperature is varying.
(ii) The blended product should be as close to the
referral temperature as possible. This will
decrease the "referral error".
(iii) The temperature measurement at the
analyser should be as accurate as possible. Any
temperature measurement error will
significantly affect the referral accuracy. (For
example, it is well known that the viscosity of
cool bunker fuel changes dramatically with
temperature.)
• The analyser should not be affected by sunlight
(temperature change). Thermal insulation around
the analyser and temperature elements is always
a good idea