Lovibond
®
PFXi Series Operator’s Instruction Manual V1.6
Page 46 of 53
Factors Influencing Inter-Instrument Differences in
Lovibond
®
Colour Measurements
A common query relates to inconsistencies in the Lovibond
®
Colour values obtained for an
individual sample when using different instruments (for example, an automatic Tintometer
®
Colorimeter such as the PFX995 and a visual instrument such as the Tintometer
®
Colorimeter
Model E or F, or two different visual instruments). There are many reasons why such
inconsistencies can arise We have attempted to provide below a detailed list of the main
factors which influence inter-instrument differences that should help you to resolve these
queries. These factors fall into four main categories:
Poor maintenance of a visual instrument
Comparison of different instrument versions
Incorrect use of visual instrument
Limitations and errors associated with automatic measurement
Poor Maintenance of a Visual Instrument
The Tintometer
®
Colorimeter Model F or E is a precision optical instrument and any
discoloration of the white surfaces or dirt on the various optical components will affect the
nature and balance of illumination within the instrument and result in false readings. As a
result, for consistency and accuracy in colour measurement, the Tintometer
®
Colorimeter
should be kept as clean as possible and the whiteness of the sample chamber and the white
reference maintained. Particular attention should be given to the following areas:
Dirt and grease on the glass filters and racks. These can be cleaned with a soft cloth or
washed gently with warm soapy water.
Dust and dirt which gathers in the optical viewing system and can settle on the lens
and correction filter. If dirty the optical viewing system can be dismantled and the
components cleaned with a suitable soft cloth. Be sure to reassemble correctly (see
Tintometer
®
Colorimeter manual).
Discoloration of the white reference. Periodic replacement is necessary to maintain
accuracy of measurement.
Light source discoloration. In the Tintometer
®
Model E and earlier models the tungsten
bulbs will discolour with age so that the instrument’s illumination is no longer standardised.
As a result, the bulbs should be changed periodically.
Discoloration and spillage in the white light sample chamber. It is important to remove
any spillage immediately and clean the chamber area.
Dirt on the bulb diffuser plates reducing the amount of illumination to the sample. These
should be cleaned or replaced if dirty.
Comparison of Different Instrument Versions
Users often assume that there is only one version of the Tintometer
®
Model E and Model F
Colorimeters; in fact, these instruments have for some time been supplied in slightly varying
formats to meet the requirements of national and international standard test methods which
specify use of the Tintometer
®
. In particular, BS 684 Section 1.14, ISO/FDIS 15305 and
AOCS Cc13e-92, all standard test methods for the determination of Lovibond
®
colour of
animal and vegetable fats and oils, specify the use of the Model F (BS 684) (previously the
Model E version AF905). These instruments include racks, which are fitted with colourless
glass compensating slides in the sample field and a black sheath to prevent light entering the
sides of the sample cell; they will give different readings to the standard Tintometer
®
Colorimeter versions and to automatic Lovibond
®
instruments.
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