Лако-красочные материалы — производство

How strong is an odour? A number of different types of sensory scales are used to measure perceived intensity of odour, two examples of which are given in Figure 8.1. Alternatively, panellists can be trained to use a form of scaling whereby they alot their own scores to the perceived intensity of odours and score subsequent odours in ratio to one another; this is known as ratio scaling, and it allows a more flexible and arguably more accurate measurement of perceived intensity.

When measuring odour intensity it is important to be aware of Stevens’s law, which states that equal changes in stimulus magnitude (5) produce the corresponding change in perceived intensity (/). The law can be expressed as a power function, as in equations (1) and (2);

I = cSk (1)

or

log I = к log S + log c (2)

i. e. the log of perceived intensity is directly related to the log of the stimulus magnitude.

The increase in perceived intensity with concentration can be represented by a straight line, as shown in Figure 8.2, for odorants A and B. The slope indicates how fast odour intensity rises with concentration and the intercept defines the detection threshold. There are two important characteristics of this type of data:

—At higher perfume concentrations a larger increase in concentra­tion is necessary to give the same change in perceived intensity.

—At different concentrations of two odorants the rank order of their perceived odour intensity can change. This is true for odorants A and В in Figure 8.2. At log Су, odorant A is stronger than odorant В but at log Cx odorant В is perceived as stronger than odorant A.

Structured scale

0 No odour

1 Very weak (threshold)

2 Weak

3 Medium strong

4 Strong

5 Very strong

Figure 8.1 Intensity scales