An olfactometer is an instrument used to detect and measure ambient odor dilution. Olfactometers are used in conjunction with human subjects in laboratory settings, most often in market research, to quantify and qualify human olfaction. Olfactometers are used to gauge the odor detection threshold of substances. To measure intensity, olfactometers introduce an odorous gas as a baseline against which other odors are compared.
Many scientists use the term "olfactometer" to refer to a device used to study insect behavior in presence of an olfactory stimulus. It consists of a tube with a bifurcation (with "T" or "Y" shape) where an insect walks and decides between two choices, usually clean air versus air carrying an odor. This is why this device is also called dual choice olfactometer.
Alternatively, an olfactometer is a device used for producing aromas in a precise and controlled manner.
A flow-olfactometer is a complex instrument for creation of well defined, reproducible smell or pain stimuli in the nose without tactile or thermal stimulation. Stimulus rise time is fast enough to allow for recording of Olfactory Evoked Potentials (OEPs).
How a flow-olfactometer works
A flow-olfactometer produces a constant heated and humidified flow of pure air. This air flow runs continuously to the subjects nose. For the length of the stimulus pulse the continuous air flow is replaced by a bloc of odorized air.
Dynamic Dilution Olfactometer
The new generations of dynamic dilution olfactometers quantify odors using a panel and can allow different complementary techniques:
- odor concentration and odor threshold determination
- odor suprathreshold determination with comparison to a reference gas
- hedonic scale assessment to determine the degree of appreciation
- evaluation of the relative intensity of odors
- allow training and automatic evaluation of expert panels
These analyses are often used in site diagnostics (multiple odor sources) performed with the goal of establishing odor management plans.
Verifying odorant level in natural gas
Natural gas odorant concentrations are required to be readily detectable at one-fifth of the lower flammable limit of the gas by state and federal regulation. Many gas companies utilize olfactometers to verify this standard. The ASTM has published a standard test method for this determination.
Field olfactometers are portable devices with a source of clean filtered air and a dilution system based on several calibrated orifices: the assessor may gradually reduce the dilution of external air until he perceives its odour, obtaining its D/T value (dilution to threshold). The SM100 Field Olfactometer allows accurate quantification of ambient odour strength using the same basic theory of lab based olfactometers. 
CEN 13725:2003 - Air quality - Determination of odour concentration by dynamic olfactometry; German version EN 13725:2003.
- Electronic noses, GC/MS systems, and human sensory panels provide varied solutions for product-odor concerns
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- Otálora-Luna F, Hammock J, Alessandro RT, Lapointe SL, and Dickens JC (2009) Discovery and characterization of chemical signals for citrus root weevil Diaprepes abbreviatus. Arthropod-Plant Interact. DOI 10.1007/s11829-009-9058-7.
- "ASTM D6273 - 08 Standard Test Methods for Natural Gas Odor Intensity". West Conshohocken, PA: ASTM International. 2008. Retrieved July 15, 2012.
- Maurizio Benzo,Alice Mantovani,Alberto Pittarello, (2012) Measurement of Odour Concentration of Immissions using a New Field Olfactometer and Markers’ Chemical Analysis. ISBN 978-88-95608-21-1; ISSN 1974-9791
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