Lovibond PFXi 950 - Page 47

Lovibond
®
PFXi Series Operator’s Instruction Manual V1.6
Page 47 of 53
Incorrect Use of Visual Instruments
Incorrect use of neutral racks. The two neutral racks included with the Tintometer
®
Colorimeter should be used to dull the sample so that the brightness in sample field and the
brightness in the comparison field are comparable. Many visual instrument users fail to use
neutral glasses; the result will be a lighter colour measurement to compensate for brightness
in the sample field.
Inappropriate choice of path length. The optical path length of the cell used should be
related to the colour intensity of the sample. As a guide, it is advisable to restrict the colour
intensity of the sample to less than a total of 30 - 40 Lovibond
®
units. Using a shorter path
length cell can reduce colour intensity.
Subjectivity of visual measurement. Visual measurements are influenced by the
discriminatory power of operators, their interpretation of a colour match and physiological
factors such as age, eye fatigue and colour vision.
Limitations and Errors Associated with Automatic Measurement
Use with samples which are turbid or crystalline. This will affect colour measurement
since turbidity prevents light being transmitted through the sample.
Lack of care in sample cell cleaning and sample preparation. Any contamination, uneven
mixing or a temperature gradient might distort the light transmitted through the sample and
affect measurements.