An Olfactometry is an instrument used to detect and measure odor dilution and is used in clinical and research settings to quantify and qualify human olfaction. To measure intensity, Olfactometry introduces an odorous gas as a baseline against which other odors are compared. An Olfactometry instrument that provides sensory measures of unpleasant odors performs olfactometry. The sensory measure calls on a patient to compare the intensity of an unpleasant odor with that of a neutral reference odor of known concentration in the air. As a function of this reference odor, 1-butanol, Olfactometry allows the intensity of an odor to be quantified and its profile determined. These data can also be used to determine the persistence and threshold of an odor. Olfactometry is routinely implemented with EEG (electroencephalogram) in performing olfactory evoked potentials.

The sensory approach is still the best way to evaluate the threshold and intensity of odors. The human nose can smell an odor at concentrations below those registered by the best existing analytical instruments. From an analytical point of view, the instrument can generate referencing odor (butanol) concentrations varying from 0.001 to 50 ppm with 1% linearity. The precision error with regard to concentration, as well as the repeatability and reproducibility errors of the measurements is approximately 2%. Olfactometry provides information, not only about the olfactory threshold, but also concerning the intensity of an odor and its persistence in time and space.

During olfactometry the intensity and profile of an odor are determined by means of a series of measurements. For each measurement, the apparatus generates a new concentration of the referencing odor (butanol) which is presented to the nose of the patient by an inhalation cone. The patient then compares the intensity of the ambient odor with that of the reference odor and indicates the relative value of the two intensities on a tactile screen. At the start of each measurement cycle, the patient breathes ultra-pure air for one minute, under the control of the Olfactometry. This prevents habituation to the ambient and reference odors, by returning the nasal mucous membranes to a zero excitation level. At each new measurement cycle, the two intensities converge towards equality. The Olfactometry indicates the corresponding butanol concentration when equality is reached.